Mountain Scholar :: Browsing by Author "Niemann, Jeffrey, committee member"

Browsing by Author "Niemann, Jeffrey, committee member"

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Open Access
Assessing long-term conservation of groundwater resources in the Ogallala Aquifer Region using hydro-agronomic modeling
(Colorado State University. Libraries, 2022) Xiang, Zaichen, author; Bailey, Ryan T., advisor; Niemann, Jeffrey, committee member; Bhaskar, Aditi, committee member; Suter, Jordan, committee member
Groundwater is vital for domestic use, municipalities, agricultural irrigation, industrial processes, etc. Over the past century, excessive groundwater depletion has occurred globally and regionally, notably in arid and semi-arid regions, often due to providing irrigation water for crop cultivation. The High Plains Aquifer (HPA) is the largest freshwater aquifer in the United States and has experienced severe depletion in the past few decades due to excessive pumping for agricultural irrigation. There is a need to determine management strategies that conserve groundwater, thereby allowing irrigation for coming decades, while maintaining current levels of crop yield within the context of a changing climate. Numerical models can be useful tools in this effort. Hydrologic models can be used to assess current and future storage of groundwater and how this storage depends on system inputs and outputs, whereas agronomic models can be used to assess the impact of water availability on crop production. Linking these models to jointly assess groundwater storage and crop production can be helpful in exploring management practices that conserve groundwater and maintain crop yield under future possible climate conditions. The objectives of this dissertation are: i) to develop a linked modeling system between DSSAT, an agronomic model, and MODFLOW, a groundwater flow model to be used for evaluating long-term impacts of climate and management strategies on water use efficiency and farm profitability of agricultural systems while managing groundwater sustainably; ii) to use the DSSAT-MODFLOW modeling system in a global sensitivity analysis framework to determine the system factors (climate, soil, management, aquifer) that control crop yield and groundwater storage in a groundwater-stressed irrigated region, thereby pointing to possibilities of efficient management; and iii) to quantify the effect of groundwater conservation strategies and climate on crop yield and groundwater storage to identify irrigation and planting practices that will maintain adequate crop yield while minimizing groundwater depletion. These three objectives are applied to the hydro-agronomic system of Finney County, Kansas, which lies within the HPA. Major findings include: 1) climate-related parameters significantly affect crop yields, especially for maize and sorghum, and soybean and winter wheat yields are sensitive to a combination of cultivar genetic parameters, soil-related parameters, and climate-related parameters; 2) Climatic parameters account for 44%, 29%, 40%, and 36% variation in yield of maize, soybean, winter wheat, and sorghum; 3) Hydrogeologic parameters (aquifer hydraulic conductivity, aquifer specific yield, and riverbed conductance) have a relatively low influence on crop yields; 4) water table elevation, recharge, and irrigation pumping are considerably sensitive to soil- and climate-related parameters, while ET, river leakage, and groundwater/aquifer discharge are highly influenced by hydrogeological parameters (e.g., riverbed conductance, and specific yield); 5) the best management practice is the combination of implementing drip irrigation and planting quarter plots under both dry and wet future climate conditions. Other irrigation systems (sprinkler) and planting decisions (half-plots) can also be implemented without severe groundwater depletion. If crop yield is to be maintained in this region of the HPA, groundwater depletion can be minimized but not completely prevented. Results highlight the need for implementing new irrigation technologies, and likely changing crop type decisions (e.g., limiting corn cultivation) in coming decades in this region of the HPA. Results from this dissertation can be used in other groundwater-irrigated regions facing depletion of groundwater.
Open Access
Assessment and improvement of hydraulic disinfection efficiency of a live small drinking water system in South Africa
(Colorado State University. Libraries, 2018) Baker, Jessica L., author; Venayagamoorthy, S. Karan, advisor; Niemann, Jeffrey, committee member; Leisz, Stephen, committee member
Since the implementation of chlorination, the most common method of water disinfection, diseases such as Cholera, Typhoid Fever, and Dysentery have been essentially eliminated in the U.S. and other industrialized countries (WHO 2017). However, these nations still experience challenges in meeting drinking water standards. In 2009, the Colorado Department of Public Health and Environment contracted Colorado State University (CSU)'s Department of Civil and Environmental Engineering to address the poor hydraulic disinfection efficiency of contact tanks of small-scale drinking water systems. From this research, the Baffling Factor Guidance Manual (2014) was published, which presents innovative modifications proven to increase the hydraulic disinfection efficiency of small-scale contact tanks. The proposed innovative technology has the potential to have a significant positive impact in developing nations since at least 2 billion people worldwide use a drinking water source that is contaminated with feces (WHO 2017). Historical experience suggests that simply transporting a technology does not necessarily equate to long-lasting impact, but how that technology is transferred is critical to its sustainability. A successful solution to the need for disinfected water must be holistic, taking into consideration culture, law, politics, economics, environment, etc. The focus of this thesis is to investigate further the application of the innovative contact tank modifications of an inlet manifold and random packing material (RPM) on live systems. A case study was conducted on a small waterworks in the rural town of Rosetta, KwaZulu-Natal, South Africa, in collaboration with Umgeni Water. Physical tracer tests were conducted on a 10,000L cylindrical tank acting as the contact chamber to assess the hydraulic disinfection efficiency in terms of baffling factor (BF), before and after the installation of a 4-way inlet manifold modification. This modification resulted in a 37% improvement in the BF, increasing the contact time (CT), an important aspect of disinfection, in the cylindrical contact tank from 8.4 min-mg/L to 11.0 min-mg/L. In addition to the international case study, a pilot study was conducted at CSU to address the biofilm formation concerns of the innovative use of random packing material (RPM) in contact tanks. Preliminary results support the hypothesis that the presence of a disinfectant in the contact tank, though in the process of disinfecting the water, would mitigate the growth of a biofilm on the RPM.
Open Access
Atoll island freshwater resources: modeling, analysis, and optimization
(Colorado State University. Libraries, 2015) Wallace, Corey David, author; Bailey, Ryan, advisor; Gates, Timothy, committee member; Niemann, Jeffrey, committee member; Ronayne, Michael, committee member
Atolls consist of ring-shaped structures of small islets of varying sizes that encircle a shallow central lagoon. Freshwater supply on atoll islands is very fragile, consisting exclusively of rainwater harvested from rainwater catchment systems and groundwater extracted from the freshwater lens. Optimal water management necessitates accurate estimation of the current and future quantity of available freshwater; of principle concern is the quantity of water to be expected in the coming decades under the influence of changing rainfall patterns. In this thesis, current and future quantities of daily captured rainwater and available groundwater are investigated using a modeling approach, with a daily water balance used for rainwater catchment systems and a numerical groundwater flow model used for the groundwater system. The conjunctive use of rainwater and groundwater in a sustainable framework is also explored. Models are tested against observed data, with sensitivity analysis then performed to investigate the governing system factors on available volume of rainwater and groundwater. Future quantities are estimated for the 2010-2050 time period using climate data obtained from general circulation models contributing to the CMIP5 framework. Rainwater catchment system sensitivity and optimization analyses are carried out for a specific atoll island in Micronesia (Nikahlap, Pakein Atoll, Pohnpei State) to not only isolate parameters influential to system performance but also to identify easily amendable system shortcomings. Results from the simulations show that daily per capita water demand, catchment area, and transmission efficiency govern the volume of stored rainwater. Using simulated future climate data, household-scale design curves are developed to assist island residents in sizing their rainwater catchment systems to satisfy specified rates of reliability. Using the design curves it was determined, for example, that an average household of 4 with a rooftop catchment area of 10 m² will require a storage cistern of approximately 250 L to ensure adequate water supply 90% of the time. The three-dimensional, density-dependent groundwater flow and transport model SEAWAT is used to simulate the dynamics of the freshwater lens within the atoll geologic system. Of the eight Micronesian atoll islands modeled, five are located in eastern Pohnpei State and three are in western Yap State. Using observed values of lens thickness available for four of the islands modeled, the geologic characteristics of the upper Holocene aquifer were calibrated for both leeward and windward islands. The orientation of the islands in relation to the direction of the prevailing winds has a significant influence on the quantity of available freshwater; islands located on the leeward and windward sides of atolls have a hydraulic conductivity of 25 m day⁻¹ and 200 m day⁻¹, respectively. Sensitivity analysis is performed to identify which geologic and climatic variables have the greatest effect on the available volume of extractable groundwater. Results from steady-state simulations show that hydraulic conductivity, the depth to contact between the upper and lower aquifers, and depth of annual recharge govern the volume of the lens. Using future simulated climate data, the size of the freshwater lens is modeled from 2010-2050. Results indicate that, with the exception of islands of extremely narrow width, lens depletion will be infrequent, occurring less than 10% of the time. When the volume of captured rainwater is depleted, extractable groundwater from the freshwater lens remains the only viable source of freshwater. It is during periods of low rainfall that conjunctive use of captured rainwater and groundwater can meet island community water demand. The concurrent use of rainwater catchment and the groundwater models allows for estimation of the total available volume of freshwater on islands of various size and atoll orientation for the 2010-2050 study period. Results indicate that when the supply of captured rainwater has been depleted, there will still be an available volume of extractable fresh groundwater nearly 99% of the time. The general nature of these methods makes them further applicable to regions outside of the FSM, and may provide water resources managers with information to more effectively manage community water supply.
Open Access
Comparison of digital terrain and field-based channel derivation methods in a subalpine catchment, Front Range, Colorado
(Colorado State University. Libraries, 2012) Hastings, Blaine, author; Kampf, Stephanie, advisor; Laituri, Melinda, committee member; Niemann, Jeffrey, committee member
Understanding the reliability of digitally derived channel networks for mountainous headwater catchments is important to many water resource and land-use management applications. Digital elevation models (DEMs) have become an essential tool for an increasing array of mountain runoff analyses. The purpose of this study is to investigate the influence of digitally-derived topographic variables on channel network formation for a high-elevation glaciated watershed. To accomplish this, our objectives were to (1) test how differences in gridded DEM resolution affect spatially distributed topographic parameters of local slope (tan β), specific contributing area (αs), and topographic wetness index (TWI) derived from both eight and infinite directional flow algorithms, (2) map the actual stream channel network at Loch Vale and examine the influence of surface variables on channel initiation, and (3) evaluate the performance of common methods for deriving channel networks from gridded topographic data by comparing to the observed network. We found that coarser DEM resolution leads to a loss of detail in spatial patterns of topographic parameters and an increase in the calculated mean values of ln(αs) and TWI. Grid cell sizes above 1m result in a substantial shift in the overall cumulative frequency distributions of ln(αs) and TWI towards higher values. A field survey at Loch Vale revealed a complex and disjointed channel network, with 242 channelized points and 30 channel heads. We found no predictable relationships between channel head locations and geomorphic process domains. Analysis of variance (ANOVA) showed no statistically significant difference in mean ln(αs) and TWI for channel head locations grouped by elevation, aspect, slope, formation process or upslope land cover type. For most DEM resolutions and flow partitioning algorithms, deriving channel networks with spatially constant flow accumulation and TWI thresholds provides poor network representation. The publicly available National Hydrography Dataset (NHD) layer oversimplifies the channel network by neglecting almost all first and second order channels. Many of the DEM-derived channel networks that use spatially constant flow accumulation and TWI thresholds also do not reproduce the locations of low order channels in the observed channel network well. Assumptions of topographic control on channel initiation are not shown to be valid at Loch Vale, likely due to their inability to capture subsurface processes and geologic features important to channel formation. However, if using these topographically dependent threshold methods to delineate channel networks, we suggest the use of field-based survey data to identify appropriate thresholds. With appropriate thresholds, both 1m and 10m DEMs can produce channel networks with similar drainage densities to the observed network, even if locations of low order channels are not predicted accurately. Performance degrades for 30m DEMs, so we suggest that DEMs with resolutions coarser than 10m should be avoided for channel network delineation.
Open Access
Crossing a threshold: the legacy of 19th century logging on log jams and carbon storage in Front Range headwater streams
(Colorado State University. Libraries, 2013) Beckman, Natalie, author; Wohl, Ellen, advisor; Kampf, Stephanie, committee member; Niemann, Jeffrey, committee member; Rathburn, Sara, committee member
Instream wood has an important effect on the geomorphic and ecological function of streams, but human impacts have altered both the forests that supply wood and the streams themselves. These changes may have pushed many stream systems over a threshold past which the stream morphology and ecology do not return to their pre-disturbance state, but instead settle into a "new normal." This dissertation addresses the question of whether logging which took place in the 19th century has had lasting and significant effects on the instream wood and carbon storage of headwater streams in Colorado's Front Range. The distribution of logs within the headwaters of the Big Thompson River, North Saint Vrain Creek and Cache la Poudre River in northern Colorado were assessed to quantify the ways in which logs and forest characteristics relate to carbon storage within a stream. Characteristics of jams (size, number per kilometer) and carbon storage correlate most closely with reach-scale variables, implying that management would be most effective at the reach scale. Increased total wood load and decreased spacing between key pieces are the most important changes that can be made to promote the formation of jams within a reach. Old growth forest creates significantly different total carbon storage and partitioning of carbon storage, which extends previous work on the effects of old growth forest on terrestrial carbon to riverine environments.
Open Access
Dam overtopping and flood routing with the TREX watershed model
(Colorado State University. Libraries, 2014) Steininger, Andrew, author; Julien, Pierre Y., advisor; Niemann, Jeffrey, committee member; Kampf, Stephanie, committee member
Modeling dam overtopping and flood routing downstream of reservoirs can provide basic information about the magnitudes of flood events that can be beneficial in dam engineering, emergency action planning, and floodplain management. In recent years there has been considerable progress in computer model code development, computing speed and capability, and available elevation, vegetation, soil type, and land use data which has led to much interest in multi-dimensional modeling of dam failure, overtopping, and flood routing at the watershed scale. The purpose of this study is to ascertain the capability of the Two-dimensional, Runoff, Erosion and Export (TREX) model to simulate flooding from dam overtopping as the result of large scale precipitation events. The model has previously been calibrated for the California Gulch watershed near Leadville Colorado and was used for all of the simulations preformed for this study. TREX can simulate the reservoir filling and overtopping process by inserting an artificial dam into the digital elevation model (DEM) of a watershed. To test the numerical stability of the model for large precipitation events, point source hydrographs were input to the model and the Courant-Friedrichs-Lewy (CFL) condition was used to determine the maximum numerically stable time steps. Point sources as large as 50,000 m3/s were stably routed utilizing a model time step as small as 0.004 seconds. Additionally the effects of large flows on the flood plain were analyzed using point source hydrographs. The areal extent of floodplain inundation was mapped and the total areal extent of flooding was quantified. The attenuation of watershed outlet discharge due to upstream dams was analyzed. Three probable maximum precipitation (PMP) events and three estimated global maximum precipitation (GMP) events (the 1 hour, 6 hour, and 24 hour duration events), were simulated. Larger duration rainstorms had lower rainfall intensities but larger runoff volumes. A series of artificial dams ranging from 5 to 29 meters high were inserted into the DEM in sequential simulations and the attenuation of the downstream flood wave was quantified. The maximum attenuation of the peak discharge at the outlet of the watershed was 63% for an 18 meter high rectangular dam for the 1 hour PMP event, 58 % for a 20 meter high dam for the 6 hour PMP event, and 46% for a 29 meter high dam for the 24 hour duration PMP event. The same analysis was done using estimated global maximum precipitation (GMP) events. The maximum attenuation of the peak discharge at the outlet of the watershed was 59% for a 23 meter high rectangular dam for the 1 hour GMP event, 21 % for a 29 meter high dam for the 6 hour GMP event, and 9% for a 29 meter high dam for the 24 hour duration GMP event.
Open Access
Effect of mountain pine beetle kill on streamflow generation mechanisms
(Colorado State University. Libraries, 2016) Wehner, Christine Elisabeth, author; Stednick, John D., advisor; Fassnacht, Steven R., committee member; Niemann, Jeffrey, committee member
The mountain pine beetle (Dendroctonus ponderosae) is an endemic species to Colorado, but a recent epidemic resulted in the mortality of millions of acres of lodgepole pine forest in Colorado since 2002. This study examined the effect of the mountain pine beetle kill on streamflow generation mechanisms using different tracer methods. Eleven nested watersheds with varying level of beetle-killed forest area (47.1% to 97.4%) were chosen for study. Groundwater, surface water, and precipitation samples were taken and analyzed for stable isotope composition (2H and 18O), specific conductivity, and chloride concentrations. Four methods were employed to partition sources of streamflow, or streamflow generation mechanisms (SGM), in beetle-killed watersheds. Stable isotopes (2H and 18O) were used to determine mean fractional contribution of each source (groundwater, rain, and snow) to streamflow. Rain and snow contribution were negatively correlated with beetle-killed forest area (p=0.08 and p=0.35 respectively). Groundwater was positively correlated with increasing beetle-killed forest area (p=0.23). Specific conductivity and chloride were each used in a 2-component (groundwater and precipitation) hydrograph separation. Using specific conductivity, beetle kill was negatively correlated with average groundwater contribution (ρ = -0.13), but the result was not significant (p = 0.71). Using chloride, the results were correlated (ρ=0.19), but not significant (p = 0.58). Specific conductivity and chloride measurements were then coupled in a 3-component (groundwater, rain, and snow) end member mixing analysis (EMMA). Beetle-killed forest area and fractional groundwater contribution were positively correlated (ρ=0.26), but not significant (p = 0.43). Watershed characteristics were examined to determine potential metrics of groundwater contribution. Mean watershed elevation displayed a significant negative correlation with mean groundwater contribution (p = 0.08).
Open Access
Ensemble-based analysis of extreme precipitation events from 2007-2011
(Colorado State University. Libraries, 2012) Lynch, Samantha, author; Schumacher, Russ, advisor; Johnson, Richard, committee member; Niemann, Jeffrey, committee member
From 2007 to 2011, 22 widespread, multiday rain events occurred across the United States. This study makes use of the European Centre for Medium-Range Weather Forecasts (ECMWF), the National Centers of Environmental Prediction (NCEP), and the United Kingdom Office of Meteorology (UKMET) ensemble prediction systems (EPS) in order to assess their forecast skill of these 22 widespread, precipitation events. Overall, the ECMWF had a skillful forecast for almost every event, with an exception of the 25-30 June 2007 event, the mesoscale convective vortex (MCV) over the southern plains of the United States. Additionally, the ECMWF EPS generally outperformed both the NCEP and UKMET EPS. To better evaluate the ECMWF, two widespread, multiday precipitation events were selected for closer examination: 29 April-4 May 2010 and 23-28 April 2011. The 29 April-4 May 2010 case study used ECMWF ensemble forecasts to explore the processes responsible for the development and maintenance of a multiday precipitation event that occurred in early May 2010, due to two successive quasi-stationary mesoscale convective systems. Locations in central Tennessee accumulated more than 483 millimeters (19 inches) of rain and the city of Nashville experienced a historic flash flood. Differences between ensemble members that correctly predicted heavy precipitation and those that did not were determined in order to determine the processes that were favorable or detrimental to the system's development. Statistical analysis was used to determine how synoptic-scale flows were correlated to area- averaged precipitation. For this particular case, the distribution of precipitation was found to be closely related to the strength of an upper-level trough in the central United States and an associated surface cyclone, with a weaker trough and cyclone being associated with more precipitation in the area of interest. The 23-28 April 2011 case study also used ECMWF ensemble forecasts to explore the processes responsible for the development and maintenance of a multiday precipitation event. This event was associated with persistent heavy rainfall, flooding more than six states lining the Mississippi River. In this case, the largest difference in the ensemble members' forecasts was the strength of the upper-level trough and associated occluded low, as well as the speed at which this system moved off to the east. These relatively small differences in the height field ultimately resulted in different forecasts of precipitation over the Mississippi Valley. This sensitivity to small-scale differences in the initial conditions highlights the importance of using ensembles for predicting the development of precipitation systems over both land and ocean. Comparison between the 29 April-4 May 2010 and 23-28 April 2011 widespread precipitation events provide information regarding which of the two case studies was better predicted in relation to both location and amount of precipitation. Heavy rainfall totals, exceeding the 100 and 150 mm threshold, were better anticipated for the 29 April-4 May 2010 event, while location of the precipitation was better predicted for the 23-28 April 2011 widespread rain event.
Open Access
Evaluation of spatially dependent on-site detention basin policies
(Colorado State University. Libraries, 2015) Augustine, Andrew John, author; Roesner, Larry, advisor; Niemann, Jeffrey, committee member; Gironás, Jorge, committee member; Stednick, John, committee member
Stormwater detention basins are typically used for stormwater control in many communities across the United States. They are commonly constructed downstream of every new development to control post-development runoff, and are called "on-site" detention basins. It has been shown by multiple authors in the literature that the design of on-site detention basins with no consideration of their location (non-spatially dependent policies, or Non-SD) in the watershed can actually increase peak flows above post-development peaks that would occur in the absence of on-site detention basins. This is caused by on-site detention basins delaying the peak release of a particular subwatershed and combining with other peak flows in the watershed (McCuen 1974; McCuen 1979; Emerson et al. 2005). Strategies to combat this problem have been reported, but metrics used to judge their success are limited to the main channel of the watershed or the watershed outlet only, leaving its impact in the remaining other watershed locations unknown. In addition, some strategies have recommended increasing the storage of on-site detention basins, but this approach would increase construction and maintenance costs and reduce the amount of land available to developers. Validation of increased peak flows throughout the watershed when Non-SD policies are used to design on-site detention basins compared to no on-site detention in the watershed was investigated first. The Non-SD policies used in this study controlled the post-development 10 and 100-year peak flows to flows at or below their respective pre-development peak flows (Non-SD 1), and controlled the post-development 100-year peak flow to flows at or below the 2-year pre-development peak flow (Non-SD 2). Next, spatially dependent policies (SD policies) were created by altering the peak flow release from on-site detention basins that would have occurred under a Non-SD policy based on its location in the watershed. These peak flows were altered using a linear model and a piece-wise linear model. Results from SD policies were compared to those from Non-SD policies. Metrics used to evaluate the effectiveness of the on-site detention basin policies (both SD and Non-SD) were peak flows throughout the watershed and total watershed storage. All policies were tested on a watershed in Fort Collins, Colorado using the Urban Morpho-climatic Instantaneous Unit Hydrograph model. Results indicate that Non-SD polices effectively reduce peak flows throughout the watershed, and do not increase peak flows compared to a policy that uses no on-site detention. When compared against Non-SD 1, SD policies derived from the linear equation were successful at reducing peak flows at some 2nd and 3rd order channel and pipe intersections in the upper half of the watershed, while increasing peak flows at 2nd order channel and pipe intersections in the lower half of the watershed. The remaining intersections were not effected by this SD policy, and the total watershed storage was shown to increase. SD policies derived from the piece-wise linear model increased peak flows at 2nd order channel and pipe intersections in the lower half of the watershed. The remaining intersections were not affected by this SD policy, and watershed storage was shown to slightly decrease. When compared to Non-SD 2, SD policies had little to no effect on peak flows at any location in the watershed or on the watershed storage.
Open Access
Evaluation of stress coefficient methods to estimate crop evapotranspiration
(Colorado State University. Libraries, 2015) Kullberg, Emily G., author; Chávez, José L., advisor; DeJonge, Kendall, committee member; Niemann, Jeffrey, committee member; Schipanski, Meagan, committee member
Increased competition for water resources is placing pressure on the agricultural sector to remain profitable while reducing water use. Remote sensing techniques have been developed to monitor crop water stress and produce information for evapotranspiration (ET) based irrigation scheduling decisions. Use of stress detection methods allows producers to avoid exceeding set crop water stress levels and keep operations sustainable under limited irrigation despite some yield reduction. Remote sensing data such as spectral reflectance and infrared canopy temperature can be used to quantify crop water stress, often through the use of vegetation indices calculated from the near-infrared and red bands and temperature indices calculated from the thermal wavelength, respectively. Reference ET methods estimate water use based on crop characteristics and climactic parameters assuming optimum soil water conditions. In order to adjust crop ET for water limited conditions such as drought or water allocation restrictions, ET scaling techniques that are sensitive to crop development and stress are necessary. The performance of five remote sensing techniques to estimate corn ET under drought conditions in Northern Colorado were evaluated: one method based on air temperature, canopy temperature and relative humidity (Crop Water Stress Index (CWSI)), three methods based strictly on canopy temperature including Degrees Above Non-Stress (DANS), Degrees above Canopy Threshold (DACT), and Temperature Ratio, and one method based on multispectral vegetation indices (NDVI Ratio). Data were collected during 2010 through 2013 growing seasons at the USDA-ARS Limited Irrigation Research Farm near Greeley, CO. Varying water deficit levels were imposed on corn (Zea mays L.) under pressurized drip irrigation. ET estimates from the five remote sensing techniques were compared to soil water balance (via neutron probe) and ET calculations. Results showed that stress coefficient methods with less data requirements such as DANS and DACT are responsive to crop water stress as demonstrated by low RMSE of ET calculations comparable to more data intensive methods such as CWSI (CWSI = 0.77 mm/day, DANS = 0.80 mm/day, DACT = 0.80 mm/day, Tc Ratio = 0.83 mm/day, NDVI Ratio = 0.85 mm/day). Detailed tables indicate which remote sensing methods are appropriate to use given certain data availability and irrigation level, in addition to providing an estimation of the associated error in ET. Using the most appropriate stress coefficient method has the potential to improve irrigation scheduling and therefore allow crops to reach the maximum possible yield given the level of deficit irrigation. Methods with fewer data requirements, such as DACT with only a single canopy temperature measurement requirement, may be more appropriate to improve on-farm water management in certain situations. Results justify use of simplified measures of stress to improve deficit irrigation water management with limited data.
Open Access
Fate of snowmelt in complex subalpine terrain
(Colorado State University. Libraries, 2016) Webb, Ryan W., author; Gooseff, Michael, advisor; Fassnacht, Steven, committee member; Ramirez, Jorge, committee member; Niemann, Jeffrey, committee member
Snow is important to human communities and natural ecosystems around the world that rely on snowmelt runoff for as much as 80% or more of streamflow. In addition to streamflow, snowmelt can drive hydrological processes such as groundwater recharge, soil moisture dynamics, forest ecosystem dynamics, and potentially cause high damage flooding. Multiple environmental controls will cause snow to vary in depth, density, and snow crystal metamorphism causing a complex three dimensional matrix of ice, air, water vapor, and liquid water (during melt) that is non-uniform across a landscape and varies in time at the daily and even hourly scale. Because of the non-uniform dynamics of snow and snowmelt processes, multi-dimensional studies are necessary to determine hydrological flow paths during spring snowmelt. The goal of this dissertation is to investigate the physical processes that control the fate of snowmelt during spring runoff in complex subalpine terrain. These processes were investigated through 1) observing the diurnal pattern of snowmelt in Colorado's Front Range, 2) testing the diversion potential of hydraulic barriers within a layered snowpack through numerical modeling, 3) collecting field data to investigate the spatio-temporal patterns of water distribution during spring snowmelt, and 4) analyzing a network of soil moisture sensors in California's Southern Sierra Nevada to determine the variability of infiltration in a headwater catchment. Observations of the diurnal temporal pattern of snowmelt resulted in a relatively simple method to capture the outflow from a snowpack using hourly snow water equivalent data. The resulting temporal pattern is comparable to design rainfall distribution types specifically for snowmelt that can be important for flood risk analysis or design of channels in previously unmonitored headwater systems. The observed temporal patterns were also used to inform numerical simulations in the modeling package TOUGH2 that utilized additional data from NASA CLPX datasets to simulate meltwater percolation through a melting snowpack. Results of this component of the dissertation displays the potential for hydraulic barriers to form on south, flat, and north aspect hillslopes and potentially divert downward flowing water at similar scales as the topographic or land cover variability. Hydraulic barriers in simulations were permeability barriers only on the south and flat aspect slopes and capillary barriers only on the north aspect slopes. The dynamic nature of a snowpack in the presence of water implies that the capillary barriers are likely short-lived relative to permeability barriers and thus capillary barriers may be important at the day or week timescale and permeability barriers may be more influential at the monthly or seasonal time scale. Field observations near Steamboat Springs, Colorado were made for above normal, relatively normal, and below normal snow seasons including measurements of bulk snow water equivalent and soil moisture on varying slope, aspect, soil parameters, and canopy conditions with results displaying the variability from these influences. Evidence was present of meltwater flowing above the soil surface and through the snowpack. At the base of the north aspect slope the water table rose above the soil surface and the snowpack added storage capacity to the vadose zone. The variability of snowmelt and resulting soil moisture and infiltration dynamics was supported by the analysis of a network of soil moisture sensors in California’s Southern Sierra Nevada. This component of the dissertations displayed the high variability of wetting and drying dynamics beneath a snowpack at the sub-hillslope and watershed scale. Results of this dissertation display that the snowpack acts as an extension of the vadose zone during spring snowmelt and that one-dimensional assumptions are not appropriate in headwater catchments during this time. Consideration of the snowpack and soil together will improve modeling, remote sensing, and water balance calculations for hydrologic studies during spring snowmelt and improvements upon allocation of streamflow, groundwater recharge, and evapotranspiration.
Open Access
Headwater stream morphology and sensitivity to development in the Piceance Basin of western Colorado
(Colorado State University. Libraries, 2016) Garrett, Krista K., author; Wohl, Ellen, advisor; Rathburn, Sara, committee member; Niemann, Jeffrey, committee member
Headwater streams are important components of watershed networks, but are less studied than larger channels and lack regulatory protection. Despite the small size of these streams, they have a disproportionate impact on the health of the watershed. Development of energy resources in the Piceance Basin of western Colorado is potentially causing significant changes in water and sediment yields to these headwater streams through the construction of roads and infrastructure. Additionally, the importance of headwater streams implies that understanding channel initiation is valuable for delineating and managing headwater stream systems. This research investigates two aspects of headwater streams: the potential impacts of energy development on channel morphology and the characterization of channel heads in western Colorado. The study focusing on channel morphology and energy development tests three hypotheses: 1) the morphology of headwater streams proximal to energy development is significantly different than otherwise analogous streams, 2) stream sensitivity to development will vary with respect to underlying lithology, and 3) stream sensitivity to development will vary with respect to stream gradient. The study exploring channel heads in western Colorado has two main objectives: 1) examine the effects of surface and subsurface flow, underlying lithology, and local gradient on channel head characteristics, and 2) examine differences between channel heads in diverse study regions by comparing this dataset to published datasets. A total of 94 stream reaches were chosen for assessing channel response to energy development. Of these, 49 reference reaches have little or no upstream disturbances and 45 impacted streams are located immediately downstream of a road or well pad. Three cross-sections per reach were surveyed to determine gradient and width to depth ratio; this ratio was used to represent channel morphology. A variety of statistical methods, including ANOVA and pairwise comparisons, were used to investigate the influence of energy development on channel morphology. This study found limited connection between energy development and headwater channel morphology. Although the morphology of impacted stream reaches is not significantly different from reference reaches, there is a relationship between channel morphology and distance to impact. Additionally, 38 channel heads were selected for analysis, including both channel heads with surface and subsurface flow, and channel heads with underlying shale and sandstone lithology. ArcGIS was used to calculate channel head parameters, including contributing drainage area and local gradient. Boxplots and the non-parametric Wilcoxon Rank Sum test were used to compare the variables drainage area, local gradient, and basin length between sandstone and shale lithologies and between subsurface and surface flows. Regression equations and pairwise comparisons were used to compare datasets from differing geographic regions. Channel heads with subsurface runoff have significantly different characteristics than channel heads with surface runoff. Differences are also present between channel heads with different underlying lithologies. No notable differences were found between channel heads located in western Colorado and other study regions.
Open Access
High groundwater in irrigated regions: model development for assessing causes, identifying solutions, and exploring system dynamics
(Colorado State University. Libraries, 2021) Deng, Chenda, author; Bailey, Ryan T., advisor; Grigg, Neil, committee member; Niemann, Jeffrey, committee member; Paustian, Keith, committee member
Waterlogging occurs in irrigated areas around the world due to over-irrigation and lack of adequate natural or artificial drainage. This phenomenon can lead to adverse social, physical, economic, and environmental issues, such as: damage to crops and overall land productivity; soil salinization; and damage to homes and building foundations. Solutions to waterlogging include implementation of high-efficient irrigation practices, installation of artificial drainage systems, and increased groundwater pumping to lower the water table. However, in regions governed by strict water law, wherein groundwater pumping is constrained by impact on nearby surface water bodies, these practices can be challenging to implement. In addition, current engineering and modeling approaches used to quantify soil-groundwater and groundwater-surface water interactions are crude, perhaps leading to erroneous results. An accurate representation of groundwater state variables, groundwater sources and sinks, and plant-soil-water interaction is needed at the regional scale to assist with groundwater management issues. This dissertation enhances understanding of major hydrological processes and trade-offs in waterlogged agricultural areas, through the use of numerical modeling strategies. This is accomplished by developing numerical modeling tools to: (1) analyze and quantify the cause of high groundwater levels in highly managed, irrigated stream-aquifer systems; (2) assess the impact of artificial recharge ponds on groundwater levels, groundwater-surface water interactions, and stream depletions in irrigated stream-aquifer systems; (3) and gain a better understanding of plant-soil-water dynamics in irrigated areas with high water tables. These objectives use a combination of agroecosystem (DayCent) and groundwater flow (MODFLOW) models, sensitivity analysis, and management scenario analysis. Each of these sub-objectives is applied to the Gilcrest/LaSalle agricultural region within the South Platte River Basin in northeast Colorado, a region subject to high groundwater levels and associated waterlogging and infrastructure damage in the last 7 years. This region is also subject to strict water law, which constrains groundwater pumping due to the effect on the water rights of the nearby South Platte River. Results indicate that recharge from surface water irrigation, canal seepage, and groundwater pumping have the strongest influence on water table elevation, whereas precipitation recharge and recharge from groundwater irrigation have small influences from 1950 to 2012. Mitigation strategy implementation scenarios show that limiting canal seepage and transitioning > 50% of cultivated fields from surface water irrigation to groundwater irrigation can decrease the water table elevation by 1.5 m to 3 m over a 5-year period. Decreasing seepage from recharge ponds has a similar effect, decreasing water table elevation in local areas by up to 2.3 m. However, these decreases in water table elevation, while solving the problem of high groundwater levels for residential areas and cultivated fields, results in a decrease in groundwater discharge to the South Platte River. As the intent of the recharge ponds is to increase groundwater discharge and thereby offset stream depletions caused by groundwater pumping, mitigating high water table issues in the region can be achieved only by (1) modifying fluxes of sources and sinks of groundwater besides recharge pond seepage, or (2) modifying or relaxing the adjudication of water law, which dictates the need for offsetting pumping-induced stream depletion, in this region. The modeling tools developed in this dissertation, specifically the loose and tight coupling between DayCent and MODFLOW, can be used in the study region to quantify pumping-induced stream depletion, recharge pond induced stream accretion, and the interplay between them in space and time. In addition, these models can be used in other irrigated stream-aquifer systems to assess baseline conditions and explore possible effects of water management strategies.
Embargo
Improving soil property predictions for applications in tailings and terramechanics
(Colorado State University. Libraries, 2024) Bindner, Joseph R., author; Scalia, Joseph, advisor; Atadero, Rebecca, advisor; Bareither, Christopher, committee member; Niemann, Jeffrey, committee member; Ham, Jay, committee member
Soil properties are used by engineers and scientists to better understand the state and behavior of soils. For example, soil properties can be used to estimate surficial soil strength for vehicle mobility models and can be used to better understand the engineering characteristics of mine waste (tailings) stored in tailings storage facilities. Soil and tailings properties often have high spatial variability and often require high resolution data for engineering analyses. Standard laboratory procedures are commonly used to determine soil properties but are often impractical for large spatial extents. While some existing soil data products provide estimates of surficial soil properties, the fidelity of soil data products is often poorly understood and insufficient for many applications. Additionally, some field tests used to estimate soil properties, such as the cone penetration test (CPT), rely on empirical correlations that cannot be used for some soils. There remains a need for procedures which improve the speed and accuracy of soil property estimates across large spatial extents. The objectives of this study are to (i) evaluate how surficial soil moisture and soil strength vary with soil and landscape attributes across a large spatial extent, (ii) explore the use of field-based hyperspectral sensing and machine learning for the prediction of surficial soil properties across a landscape, and (iii) assess the use of laboratory hyperspectral sensing and machine learning for the prediction of tailings properties for potential application in situ via direct push methods. Soil and landscape attributes were determined at sampling locations across a semi-arid foothills region and used to assess how soil moisture and soil strength vary with soil and landscape attributes. Then, hyperspectral data were captured at select sampling locations and used to train and assess the performance of a convolutional neural network (CNN) for the predictions of soil properties. Finally, a diverse tailings-hyperspectral dataset was prepared in the lab and used to train and assess a CNN to provide proof of concepts for prediction of material properties relevant to TSF stability analyses.
Open Access
Influence of the Madden-Julian Oscillation and Caribbean Low-Level Jet on east Pacific easterly waves
(Colorado State University. Libraries, 2018) Whitaker, Justin W., author; Maloney, Eric, advisor; Bell, Michael, committee member; Niemann, Jeffrey, committee member
The east Pacific warm pool exhibits basic state variability associated with the Madden-Julian Oscillation (MJO) and Caribbean Low-Level Jet (CLLJ), which affects the development of easterly waves (EWs). This study compares and contrasts composite changes in the background environment, eddy kinetic energy (EKE) budgets, moisture budgets, and EW tracks during MJO and CLLJ events. While previous studies have shown that the MJO influences jet activity in the east Pacific, the influence of the MJO and CLLJ on EWs is not synonymous. The CLLJ is a stronger modulator of the ITCZ than the MJO, while the MJO has a more expansive influence on the northeastern portion of the basin. Anomalous low-level westerly MJO and CLLJ periods are associated with favorable conditions for EW development paralleling the Central American coast, contrary to previous findings about the relationship of the CLLJ to EWs. Easterly MJO and CLLJ periods support enhanced ITCZ EW development, although the CLLJ is a greater modulator of EW tracks in this region, which is likely associated with stronger moisture and convection variations and their subsequent influence on the EKE budget. ITCZ EW growth during easterly MJO periods is more reliant on barotropic conversion than in strong CLLJ periods, when EAPE to EKE conversion associated with ITCZ convection is more important. Enhanced background state moisture anomalies during strong CLLJ periods lead to stronger diluted CAPE anomalies in the mean state and EWs that support convection. Thus, the influence of these phenomena on east Pacific EWs should be considered distinct.1 1 This abstract is adapted from the abstract of: Whitaker, J.W., and E. D. Maloney, 2018: Influence of the Madden-Julian Oscillation and Caribbean Low-Level Jet on East Pacific Easterly Wave Dynamics. J. Atmos. Sci., in press. ©American Meteorological Society. Used with permission.
Open Access
Initation and intensification of east Pacific easterly waves
(Colorado State University. Libraries, 2015) Rydbeck, Adam V., author; Maloney, Eric, advisor; Johnson, Richard, committee member; Birner, Thomas, committee member; Niemann, Jeffrey, committee member
The background atmospheric state of the east Pacific (EPAC) warm pool in which easterly waves (EWs) develop varies dramatically on intraseasonal time scales. EPAC intraseasonal variability is well known to modulate local convective and circulation patterns. Westerly intraseasonal phases are associated with westerly lowlevel wind and positive convective anomalies and easterly intraseasonal phases are associated with easterly low-level wind and negative convective anomalies. This study first investigates the perturbation available potential energy (PAPE) and perturbation kinetic energy (PKE) budgets of easterly waves composited during westerly, easterly, and neutral intraseasonal phases, respectively. During neutral and westerly intraseasonal phases, the generation of PAPE associated with perturbation diabatic heating that is subsequently converted to PKE is enhanced and is the dominant energy source for EWs. EWs draw energy from low-level barotropic conversion, regardless of phase. A novel and previously unrecognized result is the detection of strong barotropic generation of PKE at midlevels during westerly intraseasonal phases. This previously unidentified source of PKE at midlevels is in part due to strong intraseasonal modulation of the background midlevel winds. Processes associated with the local amplification of EWs in the EPAC warm pool are then explored. Developing EWs favor convection in the southwest and northeast quadrants of the disturbance. In nascent EWs, convection favors the southwest quadrant. In these quadrants, lower tropospheric vorticity is generated locally through vertical stretching that supports a horizontal tilt of the wave from the southwest to the northeast. EWs with such tilts are then able to draw energy via barotropic conversion from the background cyclonic zonal wind shear present in the east Pacific. EWs during westerly and neutral intraseasonal periods are associated with robust convection anomalies. Easterly intraseasonal periods are, at times, associated with very weak EW convection anomalies due to weaker moisture and diluted CAPE variations. The in-situ generation of EWs in the EPAC is then investigated using the Weather Research and Forecasting Model (WRF). Sensitivity tests are performed to examine the atmospheric response to the removal of external and internal EW forcing in the EPAC warm pool. External forcing of EPAC EWs is removed by filtering EWs in wavenumber frequency space from the model’s boundary forcing. Internal forcing of EWs is removed by reducing the terrain height in portions of Central and South America to suppress the strong source of diurnal convective variability in the Panama Bight. These regions of high terrain are associated with mesoscale convective systems that routinely initiate in the early morning and propagate westward into the EPAC warm pool. In both sensitivity tests, EW variance is significantly reduced in the EPAC, suggesting that both EWs propagating into the EPAC from the east and EWs generated locally in association with higher frequency convective disturbances are critical to EPAC EW variability. A new mechanism is proposed to explain the in-situ generation of EPAC EWs. Serial mid-level diurnal vorticity and divergence anomalies generated in association with deep convection originating in the Panama Bight underpin the local generation, intensification, and spatial scale selection of EW vorticity by vertical vorticity stretching. Diurnal vorticity anomalies in the Panama Bight are able to initiate disturbances capable of growing into robust EWs through a tendency to organize vorticity upscale.
Open Access
Landslide response to climate change in Denali National Park, Alaska, and other permafrost regions
(Colorado State University. Libraries, 2019) Patton, Annette, author; Rathburn, Sara, advisor; Wohl, Ellen, committee member; Singleton, John, committee member; Niemann, Jeffrey, committee member
To view the abstract, please see the full text of the document.
Embargo
Long-term analysis of groundwater depletion in the High Plains Aquifer: historical, predictive, and solutions
(Colorado State University. Libraries, 2024) Nozari, Soheil, author; Bailey, Ryan, advisor; Niemann, Jeffrey, committee member; Ronayne, Michael, committee member; Suter, Jordan, committee member
Semi-arid agricultural regions worldwide are heavily dependent on groundwater storage in a handful of large and over-exploited aquifers, such as the High Plains Aquifer (HPA) in the U.S. High Plains Region. The HPA, one of the world's largest freshwater aquifers, serves as the primary source of irrigation water in the High Plains Region. The socioeconomic development in the High Plains Region has come at the expense of significant groundwater depletion in the HPA. The ongoing depletion of the HPA poses risks to livelihoods of rural communities, local ecosystems, and national food security. Addressing this issue necessitates the formulation of groundwater management policies that aim to reduce groundwater extraction, while minimizing associated economic costs over a multi-generational timeframe, all in the context of climate change. To inform the formulation of effective policies, it is crucial to develop a suite of decision support tools that empower local managers and planners to assess the outcomes of various groundwater management policies amidst climate change. The primary goal of this dissertation is to enhance the capacity to project the future of groundwater systems in semi-arid agricultural areas, particularly within the High Plains Region, as a coupled human-natural system, under various groundwater management schemes in the face of climate change. To achieve this goal, a number of tools were developed that incorporate a spectrum of modeling approaches, from the increasingly popular data-driven models to the state-of-the-art hydro-economic models. First, a data-driven modeling framework was developed and tested that is fast to employ and yet provides reliable long-term groundwater level (GWL) forecasts as a function of climatic and anthropogenic factors. The modeling framework utilizes the random forests (RF) technique in combination with ordinary kriging and was tested for the HPA in Finney County, southwest Kansas. The introduction of groundwater withdrawal potential as a new surrogate for pumping intensity empowers the RF model to capture decline in groundwater depletion rate as the system progresses towards aquifer depletion and/or as a result of well retirement policies. The RF model was applied over the period from 2017 to 2099 using 20 downscaled global climate models (GCMs) for two representative concentration pathways (RCPs), RCP4.5 and RCP8.5. The findings indicate that, under status quo management and average climate conditions, the aquifer will no longer be able to sustain irrigated agriculture in most of the county by 2060. Additionally, the difference in climate scenarios will likely shift the aquifer's depletion time frame by up to 15 years in most of the study area. The long-term combined impact of well retirement plans and climate conditions on groundwater depletion trends imply well retirement policies do not lead to sustained groundwater savings. In the next step, an agent-based hydro-economic model (ABM-MODFLOW) was developed for a portion of the HPA in eastern Colorado and northwest Kansas, with the aim of addressing the current limitations of hydro-economic models. Through interdisciplinary collaboration, each component of the ABM-MODFLOW was particularly designed to meet specific research objectives. Planting and irrigation decisions were simulated in the ABM-MODFLOW using a detailed representation of real-world farmers. Additionally, well capacity was incorporated as a constraint on irrigation duration. A subsequent thorough validation of the ABM-MODFLOW was conducted to establish its credibility. The validation results indicate satisfactory performance in reproducing historical data and trends. They also reveal the ABM-MODFLOW's superiority over the standalone groundwater model in simulating the groundwater system. The historical simulation outcomes also underscore the impact of soil type on agents' profitability, especially for those with limited irrigation capacities. Overall, the highest profits are earned by agents with high irrigation capacities and fine soils, while the lowest are achieved by those with low irrigation capacities and coarse soils. Lastly, the ABM-MODFLOW was employed to project the coevolution of human activities, crops, and the groundwater system amidst climate change, both with and without policy interventions. The ABM-MODFLOW simulations involved 32 climate scenarios from 16 downscaled GCMs for two RCPs, RCP4.5 and RCP8.5. Additionally, three groundwater management policy instruments were explored: irrigated land retirement, irrigation well retirement, and authorized pump rate reduction. The simulation outcomes reveal that the groundwater depletion rate decreases over time, primarily due to rising summer temperatures from climate change that limit corn production, a water-intensive crop, in the region. Moreover, these rising temperatures hamper the economic benefits of policies, since the early conserved groundwater is predominantly used for winter wheat irrigation in the later years, a crop with substantially lower irrigation value than corn.
Open Access
Optimizing remote sensing data for actual crop evapotranspiration mapping at different resolutions
(Colorado State University. Libraries, 2024) Costa Filho, Edson, author; Chávez, José L., advisor; Venayagamoorthy, Karan, committee member; Niemann, Jeffrey, committee member; Kummerow, Christian, committee member
This study aimed to advance irrigation water management by developing and evaluating a procedure to improve the multispectral data from sub-optimal remote sensing sensors when using the optimal spectral resolution for a given remote sensing (RS) of crop actual evapotranspiration (ETa) algorithm. Data have been collected at three research sites in Colorado under different irrigation systems, soil textures, and vegetation types. The research site in Greeley (CO) has a five-year dataset (2017-2018 and 2020-2022). The fields in Fort Collins and Rocky Ford (CO) have data from 2020 and 2021. Three categories of ETa algorithms were evaluated in the study: The reflectance-based crop coefficient (RBCC) with three different models based on the normalized difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), and fractional vegetation canopy cover (fc), the one-source simplified surface energy balance (OSEB) based on a surface aerodynamic temperature approach, and the two-source surface energy balance algorithm (TSEB) using two different resistance approaches (parallel and series). All three ETa modeling categories use either just surface reflectance in the visible and invisible light spectrum (e.g., RED, BLUE, GREEN, Near-infrared) or a combination of multispectral and thermal data as inputs to predict crop ETa, alongside local micrometeorological data from nearby agricultural weather stations. A total of six RS of ETa algorithms were evaluated in this study. A total of five RS sensors were evaluated: three spaceborne sensors (e.g., Landsat-8, Sentinel-2, and Planet CubeSat), one proximal device (multispectral radiometer), and an uncrewed aerial vehicle (UAS). The spatial resolution of the RS sensors varied from 30 m to 0.03 m. The accuracy assessment of the crop ETa predictions considered a statistical performance analysis using, among several statistical metrics, the mean bias error (MBE) and root mean square error (RMSE), and compared estimated ETa values from all seven RS ETa algorithms with observed ETa values obtained from the Eddy Covariance Energy Balance System (Greeley and Fort Collins sites) and a weighing lysimeter (Rocky Ford). The study was divided into three stages: a) the evaluation of different remote sensing (RS) pixel spatial resolutions (scales) as inputs on the estimation of different types of data needed for estimating ETa in hourly and daily time frames; b) the development of a calibration protocol and standards for the use of different imagery spatial resolutions (scales) in RS of ETa algorithms. The calibration approach involved a novel two-source pixel decomposition approach for partitioning surface reflectance into soil and vegetation using a non-linear, physically based spectral model, machine-learning regression, and a novel spatial light extinction model (kp); c) the accuracy evaluation of resulting ETa rates from calibrated/standardized data (for each selected RS of ETa algorithms). Results of stage one of the study indicated that depending on the RS of ETa and RS sensor data (spatial and spectral resolutions), the accuracy (MBE ± RMSE) of estimated ETa predictions varied. For the NDVI and fc RBCC ETa algorithms, Sentinel-2 provided the best RS data for predicting daily maize ETa. Errors were 0.21 (5%) ± 0.78 (18%) mm/d and 0.59 (14%) ± 1.07 (25%) mm/d, respectively. For the OSEB algorithm, Planet CubeSat gave the best RS data since it provided the smallest error for hourly maize ETa, -0.02 (-3%) ± 0.07 (13%) mm/h. For the SAVI RBCC model, the MSR data provided the best results since the maize ETa error was -0.13 (-3%) ± 0.67 (16%) mm/d. For the TSEB in series and parallel, the errors when estimating hourly maize ETa were -0.02 (-3%) ± 0.07 (11%) mm/h and -0.02 (-4%) ± 0.09 (14%) mm/h, respectively when using MSR data. For stage two of the study, the best machine learning regression model for a given RS sensor data and RS of the ETa algorithm depended on the surface reflectance composite (plant or bare soil values). The best machine-learning models for adjusting RS data were the regression tree and the Gaussian Process Regression. Regarding the pixel decomposition approach based on the novel spatial light extinction coefficient model, the novel approach provided reliable predictions of kp using the different RS sensor data. The error in predicting kp was -0.01 (-2%) ± 0.05 (10%) when combining all RS sensor data for the two-year data set at LIRF (years 2018 and 2022). For stage three of the study, results showed improvements in the accuracy of crop ETa estimation after adjusting the RS data using the proposed calibration protocol. At the Greeley site, regarding the RBCC RS of ETa algorithm, adjusted data from Planet CubeSat had better performance when estimating daily crop ETa since the error was reduced from 21% to 16% for the fc-input model. For the SAVI-input model, the RS data that performed better was the UAS. Errors were reduced from -0.42 (-11%) ± 0.76 (20%) mm/d to -0.21 (-5%) ± 0.41 (11%) mm/d. For the NDVI-input model, the adjusted UAS data performed better when estimating daily maize ETa. The improved accuracy was 0.32 (8%) ± 0.40 (10%) mm/d. At the Rocky Ford site, for the fc-input model, adjusted RS optical data from the MSR performed better. Daily maize ETa error was reduced from 17% to 15%. For the SAVI-input model, the RS data that performed better was the Landsat-8, with errors being reduced from -1.84 (-28%) ± 2.61 (39%) mm/d to -1.14 (-17%) ± 1.79 (27%) mm/d. The NDVI-based RBCC model had better performance when using adjusted MSR data daily maize ETa. Regarding the OSEB RS of crop ETa approach, at the Greeley site, the OSEB-adjusted data from UAS performed better. Hourly maize ETa error was reduced from 0.11 (19%) mm/h to 0.07 (13%) mm/h for the OSEB algorithm. For the TSEB parallel algorithm, the RS data that had better performance was the Landsat-8/9 since the error was reduced from 0.19 (34%) mm/h to 0.11 (20%) mm/h. For the TSEB series algorithm, the adjusted UAS data performed better. Daily maize ETa errors decreased from 0.10 (18%) mm/h to 0.05 (9%) mm/h. In summary, this study provided an RS calibration approach to support irrigation water management through the development and evaluation of a method for enhancing optical multispectral data sourced from various RS sensors. This study also highlighted the efficacy of machine learning models, like regression tree and Gaussian Process Regression, in adjusting RS data based on surface reflectance composites. Furthermore, a novel pixel decomposition approach utilizing a spatial light extinction model effectively predicted the light extinction coefficient. Overall, this research showcases the potential of RS data adjustments in improving the accuracy of ETa estimates, which is crucial for optimizing irrigation practices in agricultural settings.
Open Access
Remote versus local controls of east Pacific intraseasonal variability
(Colorado State University. Libraries, 2012) Rydbeck, Adam, author; Maloney, Eric, advisor; Birner, Thomas, committee member; Niemann, Jeffrey, committee member
The Madden-Julian Oscillation (MJO) is the dominant mode of tropical intraseasonal variability and propagates eastward at 5 m/s with primary signals in wind and precipitation. During boreal summer, interactions between intraseasonal variability in the eastern Hemisphere and the east Pacific warm pool are often described as a local amplification of the propagating MJO. However, the precise mechanism by and degree to which intraseasonal variability in the eastern Hemisphere affects the east Pacific warm pool are not well understood. One school of thought holds that the MJO initiates a dry intraseasonal Kelvin wave response in the west Pacific that rapidly propagates into the Western Hemisphere and initiates intraseasonal convective variability there. To quantify the relationship between the source (Eastern Hemisphere) and amplification region (east Pacific warm pool), sensitivity tests in two separate models are used to determine the importance of local versus remote controls of east Pacific warm pool intraseasonal variability. The two models include the National Center for Atmospheric Research Community Atmosphere Model 3 (CAM3) and the International Pacific Research Center Regional Atmosphere Model (IRAM). The two models use different schemes to isolate the east Pacific from eastward-propagating intraseasonal variability that impinges from the west. Removing the influence of the MJO on the east Pacific warm pool in these two models reveals different insights into local versus remote control of intraseasonal variability in the east Pacific. The CAM3 produces comparable intraseasonal variability in winds and precipitation in the east Pacific when Kelvin wave signals from the west are removed, suggesting that the Eastern Hemisphere MJO helps to pace east Pacific intraseasonal variability, although east Pacific variability can exist in isolation from the MJO. Thus, the CAM3 supports independent intraseasonal variability in the east Pacific warm pool that may be phase locked to intraseasonal variability in the Eastern Hemisphere in observations. However, the IRAM has very small east Pacific intraseasonal variability when isolated from global MJO signals. The weak intraseasonal variability in IRAM may be a result of mean low-level wind biases that cause 30 to 90 day surface flux anomalies to be out of phase with 30 to 90 day precipitation and low level wind anomalies. As a result, the IRAM model does not support an independent local mode of intraseasonal variability in the east Pacific.