Browsing by Author "Sanford, William E., committee member"

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Open Access
A combined field analysis and modeling approach for assessing the impact of groundwater pumping on streamflow
(Colorado State University. Libraries, 2018) Flores, Luke, author; Bailey, Ryan T., advisor; Gates, Timothy K., committee member; Sanford, William E., committee member
The magnitude of volumetric water exchange between streams and alluvial aquifers impacts contaminant transport rates, channel erosion and sedimentation, nutrient loading, and aquatic and riparian habitat. Quantifying the interactions between stream water and groundwater is also critically important in regions where surface water and tributary groundwater are jointly administered under a prior appropriation doctrine, such as in the western United States. Of particular concern is the effect of a nearby pumping well on streamflow. When the cone of influence of a pumping well reaches a nearby stream, the resulting hydraulic gradient can induce enhanced seepage of streamflow into the aquifer or decrease the rate of groundwater discharge to the stream. The change in these rates is often modeled using analytical or numerical solutions, or some combination of both. Analytical solutions, although simple to apply, can produce discrepancies between field data and model output due to assumptions regarding stream and aquifer geometry and homogeneity of hydraulic parameters. Furthermore, the accuracy of such models has not been investigated in detail due to the difficulty in measuring streamflow loss in the field. In the first part of this thesis, a field experiment was conducted along a reach of the South Platte River in Denver, Colorado to estimate pumping-induced streamflow loss and groundwater head drawdown, and compare data against analytical modeling results. The analytical solutions proved accurate if streamflow was low and constant, but performed poorly if streamflow was high and variable. In particular, the models are not capable of accurately simulating the effects of increasing stream width and bank storage due to rapid increases in streamflow. To better account for these effects a new analytical modeling framework is introduced which accounts for all major factors contributing to streamflow loss for a given site for both periods of pumping and periods between pumping. For the reach analyzed herein, the method illustrates that pumping wells often only caused half of the given streamflow loss occurring along the reach. This method can be used in other stream-aquifer systems impacted by nearby pumping. The U.S. Geological Survey's three-dimensional finite-difference groundwater flow model, MODFLOW, was also used to assess the impacts of pumping on streamflow. While MODFLOW removes many of the restrictive assumptions that define analytical solutions, certain limitations persist when the program is applied on local, fine scales with dynamic interactions between a stream and alluvium. In particular, when the average stream width is greater than the computational grid cell size, the model will return systematically biased, grid-dependent results. Moreover, simulated streamflow loss will be limited in the range of values that can be modeled. To address these limitations, a new stream module is presented which (1) allows for streams to dynamically span multiple computational grid cells over a cross section to allow for a finer mesh; (2) computes streamflow and backwater stage along a stream reach using the quasi-steady dynamic wave approximation to the St. Venant equations, which allows for more accurate stream stages when normal flow cannot be assumed or a rating curve is not available; and (3) incorporates a process for computing streamflow loss when an unsaturated zone develops under the streambed. Streamflow loss is not assumed constant along a cross section. It is shown that most streamflow loss occurs along stream banks and over newly inundated areas after increases in upstream streamflow. The new module is tested against streamflow and groundwater data collected in a stream-aquifer system along the South Platte River in Denver, Colorado and to estimate the impact of nearby pumping wells on streamflow. When compared with existing stream modules more accurate results are obtained from the new module. The new module can be applied to other small-scale stream-aquifer systems.
Open Access
Assessing groundwater storage and groundwater level fluctuations in the area of Fort Collins, Colorado
(Colorado State University. Libraries, 2018) Almahawis, Mohammed, author; Bailey, Ryan T., advisor; Scalia, Joseph, IV, committee member; Sanford, William E., committee member
Although groundwater is the main water supply for many municipalities worldwide, shallow groundwater can adversely affect urban areas via soil waterlogging and impacts on building foundations and general city infrastructure. A quantitative assessment of groundwater levels and temporal fluctuations is needed to determine the extent to which groundwater should be managed to prevent these adverse conditions. This thesis assesses past and current groundwater storage and groundwater levels in the city limits of Fort Collins, Colorado, a moderate-sized municipality situated in the Front Range of the Rocky Mountains in the western United States. Currently, Fort Collins uses only surface water for its water supply, with the underlying unconfined alluvial aquifer mostly unused and close to ground surface. The assessment includes developing quantitative groundwater maps (depth to water table, water table elevation, and saturated thickness), estimating groundwater recharge and change in storage during large rainfall events, and defining areas with risk of high groundwater level. Observed depth to water table data from various sources was collected for two-time frames (1959-1979 and 2000-2017). The Stanford Geostatistical Modeling Software (SGeMS) was used to interpolate soil and groundwater data, and a Geographic Information System (GIS) was used to develop maps, estimate the storage, and define areas with potential risk of high groundwater level. Also, the Natural Resources Conservation Service's (NRCS) curve number method was performed to quantify recharge from high-intensity rainfall events. NRCS curve number method is a widely used method to quantify the amount of runoff due to a rainfall event. Comparing results from the two-time frames, the depth to water table in the study area has increased slightly (0.32 m) with a 3.9 m current average depth to the water table. Storage has decreased from 126.8 million m3 to 122 million m3, largely due to pumping groundwater for irrigation in the northeast area of the city limits. Approximately 10% of parcels in the Fort Collins area are at risk of high groundwater level. Most parcels along the Cache La Poudre River have problems with high groundwater level. The amount of recharge to the shallow aquifer in the Fort Collins area due to 10 and 100-year return-period storms is approximately equal to 1.9 million m3 and 3.3 million m3, respectively. Also, the percentage of the parcels at risk of high groundwater table will increase to 11% and 12%, respectively. The resulting groundwater maps, and the response of water table to rainfall events, can assist city water managers with identifying areas of potential risk to shallow groundwater conditions. In addition, the methods applied in this thesis can be used for other urban areas containing a shallow alluvial aquifer.
Open Access
Assessing impacts of rainfall patterns, population growth, and sea level rise on groundwater supply in the Republic of Maldives
(Colorado State University. Libraries, 2016) Deng, Chenda, author; Bailey, Ryan, advisor; Grigg, Neil, committee member; Sanford, William E., committee member
Groundwater resources of the Republic of the Maldives are threatened by a variety of factors including variable future rainfall patterns, continued population growth and associated pumping demands, rising sea level, and contamination from the land surface. The Maldives is composed of approximately 2,000 coral islands residing in 26 atolls in the Indian Ocean, with each coral island less than a few square kilometers in surface area and less than a few meters in elevation. This thesis uses numerical modeling techniques to assess the influence of variable rainfall patterns, increased pumping due to population growth, and sea level rise on fresh groundwater supply of the coral islands that comprise the Maldives. The density-dependent groundwater flow and solute transport model SUTRA (Saturated Unsaturated Transport) is used for all simulations, with the model simulating the spatial extent of the freshwater lens in the aquifer of the coral islands. The thesis first assesses changes in groundwater supply due to variable rainfall patterns in the coming decades, a key component of water resources management for the country. Using a suite of two-dimensional vertical cross-section models, time-dependent thickness of the freshwater lens is simulated for a range of island sizes (200 m to 1100 m) during the time period of 2011 to 2050, with recharge to the freshwater lens calculated using rainfall patterns provided by General Circulation Models (GCM) for the three distinct geographic regions (north, central, south) of the Maldives. Results show that average lens thickness of islands in all three geographic regions during the 2031-2050 time period is slightly greater than during the 2011-2030 time period, indicating a mild increase in future available groundwater supply under predicted conditions. Average lens thickness during 2011-2030 for islands of 200 m, 400 m, 600 m, and 1100 m width is 0.5 m, 3.0 m, 7.0 m, and 12.2 m, respectively, with these values increasing by 1-5% during 2031-2050 time period. However, these results do not include the effect of sea level rise. To quantify the total available groundwater on a representative island and to provide accurate simulation of the effect of radial pumping on the freshwater lens, a three dimensional model is created for the island of Gan (Area: 598 ha, Population: 4,280) to evaluate the impact of increasing pumping and sea-level rise on future groundwater resources. Simulations covering the 2012-2050 period are used to compare scenarios of future rainfall, pumping vs. non-pumping, varying rates of population growth and hence of groundwater pumping, and sea level rise (0.5 m by 2100) vs. no sea level rise. Results indicate that the total freshwater volume increases about 19% under the effects of future rainfall patterns. If moderate pumping is included, with rates increasing at 1.76% to correspond with increasing population, the volume increases only by 12%. If just considering sea level rise, then the volume decreases by 14%. With aggressive pumping, corresponding to an annual population growth rate of 9%, but no sea level rise, the volume decreases by 24%. With aggressive pumping and sea level rise, the freshwater lens is rapidly depleted. This study quantifies the major future impacts on groundwater of the atoll islands in Maldives. Similar methodologies using output from GCMs can be used for other atoll island nations, such as the Republic of Marshall Islands, Federated States of Micronesia, and Gilbert Islands. For the Maldives, results from this study can be used in conjunction with population growth estimates to determine the feasibility of including groundwater in water resources planning and management for the country.
Open Access
Comparison of the Glover-Balmer solution with a calibrated groundwater model to estimate aquifer-stream interactions in an irrigated alluvial valley
(Colorado State University. Libraries, 2014) Mages, Cale A., author; Gates, Timothy K., advisor; Bailey, Ryan T., advisor; Sanford, William E., committee member
In many alluvial valleys wherein streams are hydraulically connected to the aquifer system, understanding and quantifying the impact of aquifer stresses (e.g. pumping, injection, recharge) on streamflow is of primary importance. Due to their relative simplicity and straightforward application, analytical models such as the Glover-Balmer solution often are employed to quantify these impacts. However, the predictive capacity of such models in intensively-irrigated systems, wherein canals, spatially-varying irrigation application patterns, and spatially-variable aquifer characteristics are often present, is not well known. In this study, the Glover-Balmer solution is compared to a calibrated MODFLOW-UZF numerical model for a study area within the Lower Arkansas River Valley in southeastern Colorado, USA. Comparison is made by simulating field-scale water extraction, addition, and fallowing scenarios, and comparing the predictions by both models of stream depletion or accretion. To create an ideal comparison, inputs to the Glover-Balmer model (stress, aquifer parameters) are obtained from the calibrated numerical model. Results for a few fallowing scenarios and from 52 extraction and addition scenarios from a variety of distances from the Arkansas River show that, under certain circumstances, the two models have good agreement in results, particularly in regions close (< about 0.5 to 1 km) to the river. However, due to aquifer heterogeneity and the overall hydrologic complexity in the natural system, results of the two models often diverge, with the Glover-Balmer model typically estimating greater impacts on the stream than the MODFLOW-UZF model. Suggested considerations are given for applying the Glover-Balmer solution, including the consideration of hydrologic components that may intercept or contribute to groundwater flow (such as irrigation canals, upflux to ET, groundwater storage, and tributaries), the potential influence of unsaturated zone processes, and changes in depletion/accretion locations and timing due to aquifer heterogeneity.
Open Access
Effective transmissivity in transient stream depletion
(Colorado State University. Libraries, 2015) Miller, Calvin D., author; Durnford, Deanna S., advisor; Garcia, Luis A., committee member; Sanford, William E., committee member; Stednick, John D., committee member
Quantifying the timing of streamflow depletion caused by groundwater pumping wells is a central issue in the conjunctive management of groundwater and surface-water resources. It is an important consideration in regions where water supplies and demands are offset annually by season and interannually through variable wet and dry years. Increased water demands, regulatory policy shifts, and aquifer changes have brought scrutiny to this type of stream-aquifer interaction. From this, analytical models of stream depletion have received renewed attention and numerous refinements which have focused primarily on a variety of complex boundary conditions. The question of representing aquifer heterogeneity through simplified input parameters in analytical models has not been directly examined for transient stream depletion. The objective of this research is to identify upscaled transmissivities that effectively model transient stream depletion rates caused by pumping groundwater wells in heterogeneous aquifers. Two-dimensional heterogeneity is considered, with horizontal anisotropy in spatial correlation ranges as a primary independent variable. The subject aquifer is relatively narrow, with an impermeable boundary parallel to a fully connected river boundary. Using numerical flow simulation and the Monte Carlo approach, stream depletion rate curves were computed for transmissivity fields constructed under various geostatistical models of heterogeneity. Effective (expected) and equivalent transmissivities—referring to stochastic ensemble-mean behavior and to individual realizations, respectively—were interpreted from the depletion curves using the Glover analytical solution for stream depletion in a homogeneous, bounded aquifer. The interpreted effective and equivalent transmissivities were related to statistical moments of the heterogeneous fields through power averaging. Effective transmissivity results ranged between the bounding arithmetic and harmonic means, varying with the spatial correlation structure of the transmissivity field, partly as a function of geometric statistical anisotropy. Notably, the shape of that function was similar to what has been derived analytically for steady-state, mean-parallel flow conditions in unbounded domains. Additionally, there was no apparent difference in effective transmissivity results between transient stream depletion conditions and steady-state, mean-parallel flow conditions simulated in the same test domain. Also, unlike some studies on effective permeability under various transient conditions, no time dependency was observed in effective transmissivity for the transient stream depletion case. Results were sensitive to including a nugget effect in the spatial correlation model and to non-stationarity of the transmissivity field. Results were only mildly sensitive to field variance. Ensemble-mean behavior was mildly sensitive to correlation scale, but ensemble variance was strongly sensitive to correlation scale. The latter is to be expected, but is notable for stream depletion considering that transmissivity correlation is often regional in scale and thus often large relative to the scale of the pumping well depletion problem. In such cases, the equivalent transmissivity for a given field and well location was often case-specific and not well-predicted by the expected transmissivity.
Embargo
Investigating the impact of irrigation and water storage practices on hydrologic fluxes under climate change in a highly managed river basin
(Colorado State University. Libraries, 2024) Almahawis, Mohammed K., author; Bailey, Ryan T., advisor; Grigg, Neil S., committee member; Scalia, Joseph, IV, committee member; Sanford, William E., committee member
Irrigation practices and sources can have significant impacts on water resources and the hydrologic fluxes that control these resources. To better manage water resources and future water supply, the influence of irrigation practices and management on these hydrologic fluxes should be quantified in time and space at varying scales, under potential irrigation management practices. To fulfill this objective, a surface-subsurface modeling approach was applied to simulate watershed-scale hydrologic processes in the Cache la Poudre River Basin, Colorado, USA (4,824 km2), in which both surface water irrigation and groundwater irrigation are prevalent. The model chosen for this study is the watershed model SWAT+, using the spatially distributed, physically based groundwater module gwflow, in which unconfined groundwater storage, flows, and interaction with land surface features are simulated using a collection of grid cells that represent control volumes of the aquifer. Major groundwater inflows and outflows include pumping, recharge, groundwater-channel exchange, groundwater-lake exchange, and tile drainage outflow. To investigate the impact of irrigation practices, detailed surface and groundwater irrigation routines and canal-aquifer interactions were added to the SWAT+ source code, requiring information of irrigation sources and irrigation canal locations throughout the river basin. Model calibration and testing was performed using monthly stream discharge and groundwater head. The calibrated model is used to quantify the impact of surface water and groundwater irrigation scenarios on water availability and hydrologic fluxes within the river basin. A total of 22 scenarios were conducted and grouped into five main groups: irrigation source, irrigation amount, irrigation type, canal bed thickness, and partial or full sealing of earthen irrigation canals. Using groundwater as the only irrigation source decreases groundwater discharge to streams (by 14%) due to lowering groundwater levels; converting flood irrigation to sprinkler irrigation throughout the basin decreases surface runoff by 22%; and sealing earthen canals leads to a lowering of groundwater levels, which decreases groundwater discharge to streams by 9%, leading to an overall decrease in streamflow in the Cache la Poudre River and changes to temporal patterns in streamflow. Overall, irrigation amount and type and canal sealing have a small impact on total groundwater storage, compared to changes in the percent of fields irrigated by groundwater pumping. The potential impacts of climate change on water resources and hydrologic fluxes were analyzed in this study. The calibrated SWAT+gwflow model is run under five different CMIP5 climate models downscaled by MACA, each representing two different climate emission scenarios, RCP4.5 and RCP8.5. Except for the CGCM3 (Warm) model, all climate models and emission scenarios predict an increase in the yearly average temperature. The projected variation in precipitation (that is, snow and rain) depends on the climate model used. However, the average annual precipitation across the entire basin is expected to increase by 6.1% under the RCP8.5 scenario for the NorESM1-M (Mild) model. On the other hand, the IPSL-CM5A-MR (Dry) model shows a maximum decrease rate of 6% from the average climate conditions under the RCP8.5 scenario. The analysis reveals that the IPSL-CM5A-MR-8.5 climate model in the CLP is the most severe, as it combines two climatic stressors: less precipitation and increased temperature. Runoff is observed to be reduced by 47.6%, groundwater recharge to drop by 11%, and a 0.5% reduction in groundwater storage under this climate scenario. Although the climate conditions in the past have been inconsistent, the transboundary water source that flows into the watershed has consistently maintained a stable discharge throughout the investigated historical period. This indicates the existence of regulated water management methods and agreements, irrespective of the impact of climate change. The potential effects of constructing a new reservoir were also assessed in this study, specifically focusing on the influence on streamflow and hydrologic fluxes under changing climatic conditions. The calibrated SWAT+gwflow model was run using two different CMIP5 climate models downscaled by MACA, CNRM-CM5 (Wet) and IPSL-CM5A-MR (Dry) under RCP8.5 emission scenario. The analysis revealed that the CNRM-CM5 (Wet) climate scenario had a higher average monthly diversion rate from the CLP river to the Glade Reservoir during operation months (2.1 m3/s) compared to the IPSL-CM5A-MR (Dry) scenario (1.6 m3/s). Both climate models show a consistent reduction in the average annual streamflow of the CLP river when the reservoir is present. The largest reduction in the average monthly streamflow in CLP river was observed under the IPSL-CM5A-MR (Dry) RCP8.5 with reservoir scenario for the month of June, showing a 78% decrease from the historical average streamflow. The reduction in streamflow, under the reservoir scenario, for both future climate models led to a 13% and 24% reduction in surface water irrigation for the wet and dry climate scenarios, respectively, compared to historical values. Results are helpful for informed decision-making in agriculture water management and can lead to sustainable, efficient, and equitable use of water resources, helping to address the challenges posed by water scarcity and environmental conservation.
Open Access
Measuring changes in areal extent of historic wetlands at Great Sand Dunes National Monument, Colorado 1936-1995
(Colorado State University. Libraries, 1998) Hammond, David J., author; Smith, Freeman M. (Freeman Minson), 1939-, advisor; Hoffer, Roger M., committee member; Sanford, William E., committee member
Great Sand Dunes National Monument (GRSA) is a unit of the National Park system in south central Colorado. With funding from the Colorado Historical Society, a series of studies were undertaken for an environmental history of the GRSA area and the San Luis Valley. Park managers were concerned over the disappearance of small wetlands in northwestern GRSA. The objective of this study is to document and analyze the changes to the wetlands through the study of digital, georeferenced images and to relate these changes to climatic and hydrologic factors. Ten sets of aerial photographs were obtained, from 1936 to 1995, with at least one set from each decade except for the 1940s. All photos were scanned into a digital format. A system was devised to mosaic the images prior to rectification due to the lack of ground control in the area. Land cover was digitized from the mosaics including the wetlands and sand type. Size and spatial distribution of the wetlands were analyzed. Analysis shows that the greatest total number of wetlands and acreage totals were present in the 1936 and 1937 photo sets. In 1937, 114 wetlands were found, 47% have water at the surface. By 1953 the total number of wetlands dropped to 38 and by 1975 only 22 remained, with only 1 having water at the surface. The total number of wetlands has increased in recent years primarily due to sub-irrigated meadows. A large increase in the vegetation cover has .occurred since 1936 to the present, increasing from 20% of the area in 1936 to 47% by 1995. Climatic data were collected to analyze possible causes of the changes to the wetlands but the study was limited by the lack of long-term data. Weather data is consistently available since 1948. Well data is of short term and sporadic nature. Two sources of long-term data were available. The discharge of the Rio Grande has been monitored in Del Norte, CO since 1906. A dendrochronology study was done in the area of GRSA in 1980. The precipitation data, discharge and dendrochronology data were summed, averaged or offset for monthly or annual intervals prior to the dates of the aerial photo sets. These values were correlated with the acreage of the wetlands for each of the photo years by means of linear regression. Very poor correlation resulted between the precipitation indices and wetland acreage. A surprising result came from correlation of the wetland acreage with the dendrochronology and discharge data. Over 58% of the wetlands variation can be explained by the 15 to 19 year offsets of dendrochronology data, 55% can be explained by the 20 year offset of Rio Grande discharge. These results are interpreted that the offset indices are related to the slow change in total area of the wetlands rather than fluctuations in the water table.
Open Access
Quantifying future water resources availability and agricultural productivity in agro-urban river basins
(Colorado State University. Libraries, 2022) Aliyari, Fatemeh, author; Bailey, Ryan T., advisor; Arabi, Mazdak, committee member; Bhaskar, Aditi, committee member; Sanford, William E., committee member
Climate change can have an adverse effect on agricultural productivity and water availability in semi-arid regions, as decreases in surface water availability can lead to groundwater depletion and resultant losses in crop yield due to reduced water for irrigation. Competition between urban and agricultural areas intensifies groundwater exploitation as surface water rights are sold to growing municipalities. These inter-relationships necessitate an integrated management approach for surface water, groundwater, and crop yield as a holistic system. This dissertation provides a novel integrated hydrologic modeling approach to quantify future water resources and agricultural productivity in agro-urban river basins, particularly in arid and semi-arid regions where surface water and groundwater are managed conjunctively to sustain urban areas and food production capacity. This is accomplished by i) developing an integrated hydrologic modeling code that accounts for groundwater and surface water processes and exchanges in large regional-scale managed river basins, and demonstrating its use and performance in the economically diverse South Platte River Basin (SPRB), a 72,000 km2 river basin located primarily in the state of Colorado, USA; ii) using the model to understand possible future impacts imposed by climate variation on water resources (surface water and groundwater) and agricultural productivity; and iii) quantifying the combination impacts of agriculture-to-urban water trading and climate change on groundwater resources within the basin. This dissertation presents an updated version of SWAT-MODFLOW that allows application to large agro-urban river basins in semi-arid regions. SWAT provides land surface hydrologic and crop yield modeling, whereas MODFLOW provides subsurface hydrologic modeling. Specific code changes include linkage between MODFLOW pumping cells and SWAT HRUs for groundwater irrigation and joint groundwater and surface water irrigation routines. This conjunctive use, basin-scale long-term water resources, and crop yield modeling tool can be used to assess future water and agricultural management for large river basins across the world. The updated modeling code is applied to the South Platte River Basin, with model results tested against streamflow, groundwater head, and crop yield throughout the basin. To assess the climate change impacts on water resources and agricultural productivity, the coupled SWAT-MODFLOW modeling code is forced with five different CMIP5 climate models downscaled by Multivariate Adaptive Constructed Analogs (MACA), each for two climate scenarios, RCP4.5, and RCP8.5, for 1980-2100. In all climate models and emission scenarios, an increase of 3 to 5 °C in annual average temperature is projected by the end of the 21st century, whereas variation in projected precipitation depends on topography and distance from the mountains. Based on the results of this study, the worst-case climate model in the basin is IPSL-CM5A-MR-8.5. Under this climate scenario, for a 1 °C increase in temperature and the 1.3% reduction in annual precipitation, the basin will experience an 8.5% decrease in stream discharge, 2-5% decline in groundwater storage, and 11% reduction in crop yield. In recent decades, there has been a growing realization that developing additional water supplies to address new demands is not feasible. Instead, managing existing water supplies through reallocations is necessary to tackle water scarcity and climate change. However, third-party effects associated to water transfers has limited the growing water market. This study also quantifies the combination impacts of agriculture-to-urban water trading (widely known as 'buy and dry') and climate change on groundwater availability in semi-arid river basins through the end of 21st century, as groundwater pumping increases to satisfy irrigation water lost to the urban sector. For this analysis, we use the hydrological modeling tool SWAT-MODFLOW, forced by projected water trading amounts and two downscaled GCM climate models, each for two emission scenarios, RCP4.5 and 8.5. According to the results of this study, agriculture-to-urban water trading imposes an additional basin-wide 2% reduction in groundwater storage, as compared to changes due to climate. However, groundwater storage changes for local subbasins can be up to 8% and 10% through the mid-century and end of the century, respectively.
Open Access
Trends and tree-rings: an investigation of the historical and paleo proxy hydroclimate record of the Khangai Mountain Region of Mongolia
(Colorado State University. Libraries, 2016) Venable, Niah B. H., author; Fassnacht, Steven R., advisor; Laituri, Melinda J., committee member; Sanford, William E., committee member; Brown, Peter M., committee member
The Khangai Mountain region of western central Mongolia is a diverse area of mountain, forest, steppe, and desert steppe landscapes reaching across and beyond the mountains. The tradition of nomadic pastoralism is strong in the region, with water for domestic and livestock needs supplied through lakes, springs, rivers, and wells. Herders of the region have felt impacts from the climatic extremes of the last few decades in terms of increasing temperatures and decreasing water supplies. The main objective of this dissertation is to quantify the changing climate of Mongolia through analysis of key hydrometeorological variables over space and through time. The assessments of trends in the data and the paleo proxy analyses herein address interdisciplinary research questions using multidisciplinary approaches. In closing, this work also examines how the data and analyses presented are used as objects that cross disciplinary boundaries, and can facilitate communication and collaboration between different groups. To provide context for this work, a countrywide view of changing maximum temperature, minimum temperature, and precipitation are examined using trend analyses of gridded datasets. Both minimum and maximum temperatures are significantly warming across the country. Significant decreases in precipitation are concentrated in the central and eastern parts of the country for the 50-year period of analysis. Local knowledge of hydroclimatic change provides another source of climatic information with herders of the Khangai Mountain region observing temperature increases, though the exact time period over which change has occurred varies depending upon memory. Therefore, temperature data were analyzed from five meteorological stations with varying lengths of record from 15 to 50 years and varying start periods based on the available length of record. The most highly significant changes occurred for the longest time periods and for annual average minimum temperatures. Issues of data availability, serial correlation, and homogeneity of climate records were explored using the Mann-Kendall test for trend significance and the Thiel-Sen method for determining trend slope or magnitude in precipitation and streamflow records. An additional step of prewhitening the data prior to testing was used to reduce the influence of autocorrelation on results. Homogeneity testing was also performed. Decreasing trends in annual, spring, and summer precipitation and/or streamflow were found at several Mongolian stations, particularly on the northern side of the mountains, with increasing winter precipitation trends at one site. Results were compared to analyses using Colorado data. Degradation of the Colorado hydroclimate records by shortening the time series and introducing gaps to simulate inconsistencies found in Mongolian datasets created significant trends where none previously existed. Tree-ring reconstructions of Mongolian hydroclimate variables have provided insight on multidecadal and muticentennial trends in climate variability over many other parts of the country, but that work has not been extended to contextualize the recent sharply decreasing streamflows of the Khangai Mountain region. Cores from two new sites collected in the summer of 2012 and records from eight other moisture-sensitive sites in the region were used to reconstruct streamflow for four gages. Missing streamflow data were filled by multiple imputation/predictive mean matching methods with data from six nearby meteorological stations prior to use in multiple linear regression models developed for the reconstructions. A quantitative evaluation of reconstructed and historical extremes of wet and dry conditions in each basin and qualitative analyses of event synchrony are discussed. The drought events of the last decade and a half, while extreme are not beyond the range of natural variability found over the last 300+ years in the four Khangai Mountain region rivers and could be considered plausible flow conditions for the future, particularly under a warming and possibly drying climate. Finally, this dissertation explores cross-boundary connections within each previous chapter and contributions of this work to selected goals of the Mongolian Rangelands and Resilience (MOR2) project, an interdisciplinary and cross-cultural collaboration investigating the resilience of Mongolian pastoral systems to climate change. Changes to the livelihoods of traditional nomadic pastoralists of Mongolia are not only attributable to climate, but also represent changes to socio-ecological, economic, and governmental/policy systems. The analyses of observational gridded, station-based, and paleo proxy data in this dissertation provide a quantitative foundation for continued investigations of the physical hydroclimate systems of the region and further themes developed in previous research from across Asia and within Mongolia. The results of this work will prove useful as a foundation for the development of water policy and infrastructure ideally favoring sustainable nomadic pastoral use of the region’s finite water resources under a changing climate.
Open Access
Trends in snow water equivalent in Rocky Mountain National Park and the northern Front Range of Colorado, USA
(Colorado State University. Libraries, 2016) Patterson, Glenn G., author; Fassnacht, Steven R., advisor; Laituri, Melinda J., committee member; Sanford, William E., committee member; Pritchett, James, committee member
The seasonal snowpack in Rocky Mountain National Park and the northern Front Range of Colorado, USA, within 50 km of the park, is undergoing changes that will pose challenges for water providers, natural resource managers, and winter recreation enthusiasts. Assessing long-term temporal trends in measures of the seasonal snowpack, and in the climatic factors that influence its annual accumulation and ablation, helps to characterize those challenges. In particular, evaluating the patterns of variation in those trends over different parts of the snow season provides new understanding as to their causes. This also helps to determine specific ramifications of the trends. In addition, placing the current 35-year trends in the longer context of longer-term observational records, and paleoclimate tree-ring reconstructions, provides useful comparisons of current and past trends. Finally, projections of future trends provided by linked climate and hydrologic models offer a sense of how these trends are likely to affect the snowpack of the future. Some factors such as the high elevation of the study area help to preserve conditions favorable to development of the seasonal snowpack, and hence to limit trends toward greater warming-induced melt and less precipitation falling as snow. Nevertheless, traditional snowpack measures such as April 1 snow water equivalent (SWE) show consistent declining trends over the 35-year period of record for automated snow monitoring stations in the study area. The trends are not uniform throughout the snow season, but vary significantly by month. As a result, November and March have warming and drying trends that delay the beginning of the winter snow season and reduce the traditional accumulation that formerly characterized the early spring. In contrast, the core winter months of December, January, and February have cooling and wetting trends that have been enhancing SWE during the heart of the winter. Mid-April to early May is another period during which cooling and wetting trends have been enhancing SWE, although these months also show more variability. This oscillating pattern helps to explain why there has not been a pervasive shift to earlier and lower annual peak SWE in the study area. Paleo SWE reconstructions based on tree-ring chronologies show that at least some of the recent 35-year trends in observed SWE described in this study have comparable precedents during the preceding five centuries, but we do not yet know how long the recent trends will continue. Linked climate and hydrologic models project that the observed trends are likely to continue, and that by 2050 measures such as April 1 SWE in the study area are likely to decrease by 25 percent.