Browsing by Author "McGrath, Daniel, committee member"
Now showing 1 - 13 of 13
Results Per Page
Sort Options
Item Open Access Beyond the case study: characterizing natural floodplain heterogeneity in the United States(Colorado State University. Libraries, 2023) Iskin, Emily Paige, author; Wohl, Ellen, advisor; Morrison, Ryan, committee member; McGrath, Daniel, committee member; Ronayne, Michael, committee memberWith human degradation of natural river corridors, the number of natural, functional floodplains is rapidly decreasing due to dams, diversions, artificial levees, draining, development, agriculture, and invasive species. At the same time, small- to large-scale interest in and implementation of river restoration is expanding, with floodplain restoration soon to take a starring role. To properly manage and restore processes to floodplains, we first need a broad understanding of what they look like and why. A key component of natural river-floodplain systems is heterogeneity, defined as the spatial variation of geomorphic and vegetation classes and patches across a floodplain. Heterogeneity of floodplains both reflects and influences the fluvial processes acting on floodplains and can help shape our understanding of the form and function of floodplains. To begin characterizing floodplain spatial heterogeneity, I present in this dissertation: 1) the development of a method to combine field measurements and remote sensing data products to calculate integrative landscape-scale metrics of floodplain spatial heterogeneity, and the demonstration of which metrics from landscape ecology are likely to be useful for identifying qualities of natural floodplains at four case study sites; 2) a sensitivity analysis to determine whether and how the values of the heterogeneity metrics change when spatial and spectral resolution of the input data are increased, and the extraction of underlying data from the classification results to determine whether using higher resolution data allows identification of the resulting unsupervised classes in relation to field and remote data at four case study sites; and 3) quantification of floodplain spatial heterogeneity, evaluation of whether statistically significant patterns are present, and interpretation of the statistical analyses with respect to the influence of channel lateral mobility and valley-floor space available using a complete dataset of 15 sites representing diverse floodplains across the continental United States. I found that "stacking" Sentinel-2A multispectral satellite imagery and digital elevation model topographic data allows for unsupervised classification of floodplains, and that metrics from landscape ecology can differentiate between different floodplain types. I also found via a sensitivity analysis that increasing the spatial resolution of the topographic data to finer than 10 m and including band ratios related to vegetation improves the classification results. Comparison of the field classes with the remote sensing classes allows for general interpretation of the results, but it is the heterogeneity within the broad classes that I expect is most important to these ecosystems. Lastly, through classification of 15 diverse river corridors across the United States, calculation of five heterogeneity metrics, and completion of a comparative analysis, I found that these natural floodplains have moderate aggregation of classes (median aggregation index = 58.8%), high evenness (median Shannon's evenness index = 0.934) and intermixing of classes (median interspersion and juxtaposition index = 74.9%), and a wide range of patch densities (range of patch density = 491–1866 patches/100 ha). I also found that the river corridor characteristics of drainage area, floodplain width ratio (space available), and elevation, precipitation, total sinuosity, large wood volume, planform, and flow regime (channel mobility) emerge as important variables to understanding floodplain heterogeneity.Item Open Access Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs(Colorado State University. Libraries, 2019) Siefken, Seth, author; Ettema, Robert, advisor; Thornton, Christopher, committee member; McGrath, Daniel, committee memberRock vanes (also known as stream barbs) and bendway weirs are two types of transverse rock structures used to modify the flow field in river bends. This study examines the effectiveness of the two types of structures at reducing velocity along the outer bank of river bends to protect the bank from erosion. A numerical model using the commercially available FLOW-3D software was used to evaluate the effect of various rock vane and bendway weir configurations on the flow field through two river bends typical of the Middle Rio Grande. The model was calibrated and validated using data from a previous physical model study of rock vanes. 33 different rock vane configurations were tested in the numerical model to evaluate the effect of altering planform angle, crest slope, projected length, and structure spacing. In addition, 14 different bendway weir configurations were tested to provide a comparison of the relative performance of bendway weirs and rock vanes. The numerical modeling results indicate that rock vanes are more effective at reducing the velocity along the outer bank of a bend than bendway weirs. Modelling showed that the completely submerged crest of bendway weirs allows a substantial amount of flow to pass over the crest, limiting their effectiveness in reducing velocity along the bank. In contrast, rock vanes, with a sloped crest intersecting the waterline at the design flow rate, directed more flow around the tip of the structure rather than over the crest and were much more effective at reducing velocity along the bank. Based on the modeling results, it is recommended that bendway weirs not be installed for the purpose of erosion protection along riverbanks. The reduction in velocity along the bank produced by the various rock vane configurations varied considerably with the geometry of the configuration. Based on the results, the following conclusions are made regarding rock vane geometry: (1) Rock vanes should be installed at a planform angle between 45° and 90° to the river bank. (2) There exists an optimal projected length of rock vane, which lies in the neighborhood of 1/5 to 1/3 of the channel top-width. (3) Rock vanes with a 10% crest slope perform well, although decreasing the crest slope will decrease the velocity along the outer bank and vice versa. (4) Decreasing the spacing of rock vanes decreases the velocity along the outer bank, up to a limit. A design equation was developed to predict the velocity reduction along the bank of a river bend produced by a given configuration of rock vanes, based on the geometry of the rock vanes and the river channel. The equation provided good predictions for the range of configurations tested, having a coefficient of determination r2 = 0.83 and predicting the velocity reduction along the outer bank to within 15 percentage points for all of the tested configurations.Item Open Access Controls on groundwater-surface water interaction in a glacial valley, northern Colorado(Colorado State University. Libraries, 2022) Doebley, Valerie, author; Ronayne, Michael, advisor; McGrath, Daniel, committee member; Kampf, Stephanie, committee memberIn the last few decades, scientists determined that groundwater discharge may supply a significant portion of streamflow in mountain watersheds. However, difficulties with access and drilling typically limit the use of monitoring wells to study groundwater in high-elevation, mountainous catchments. The recent installation of two 10-meter-deep monitoring wells plus several riparian wells along the South Fork of the Cache la Poudre River at the Colorado State University Mountain Campus provided an opportunity for a unique hydrogeological study at a mountainous site. Data from these wells combined with numerical groundwater modeling helped quantitively and qualitatively characterize groundwater-surface water exchange along a ~2.7-km study reach. Analyses reveal complex temporal and spatial variation of gaining and losing stream conditions within the study reach. First, well water level elevations and groundwater modeling results indicate that the South Fork is generally gaining in the upper portion of the valley and losing near the downstream end. We suggest that valley geometry and channel planform influence the spatial differences in groundwater-surface water exchange along the study reach. Second, streamflow differencing and modeling results suggest that the study reach changes between overall gaining and overall losing stream conditions multiple times between May and October. We suggest that these temporal variations in groundwater-surface water exchange are driven by seasonal changes in surface water contributions to streamflow and evapotranspiration. Third, stable isotope (δ2H, δ18O) analyses and groundwater modeling results suggest that localized recharge from moraine ponds and stream leakage are important sources of aquifer recharge. These results indicate that groundwater and surface water at the Mountain Campus are highly interdependent, and that any disturbances that impact surface water contributions to streamflow may ultimately impact the groundwater contributions as well.Item Open Access Ecological consequences of warming climes for cold-adapted species – evidence from mountain goats(Colorado State University. Libraries, 2023) Hayes, Forest Parker, author; Berger, Joel, advisor; Bailey, Larissa L., committee member; Wilson, Kenneth R., committee member; McGrath, Daniel, committee memberGlobal climate change from human activity is changing ecological communities at unprecedented rates. Coupled with recent and extraordinary loss of biodiversity, assessing the consequences for vulnerable species – and effecting proactive conservation – will be fundamental to stymieing these losses. Among the areas most strongly impacted by these changes are montane regions, which are warming at rates 2–5x the global average. Within those, cold-adapted organisms are among the most strongly impacted as they may experience thermal stress at moderate temperatures. Past species- and taxa-level responses to warming environs includes numerous concentrated extirpations at the southern peripheries of distributional ranges during the late Pleistocene. Less clear are localized capacities of cold-adapted species to mitigate thermal challenges against warming temperatures, especially through proximate behavioral and physiological adjustments. In this dissertation, I address three key tendrils of the ecological consequences of warming climes for cold-adapted species. First, I evaluate the role of snow patches in mediating the physiological impacts of warming temperatures. Despite strong associations between many taxa and cold environs, great uncertainty remains about the biological benefits, if any, of using persistent snow during summer months. Contrary to the prevalent hypothesis that persistent snow provides thermal relief for cold-adapted species, I demonstrate that use of snow patches facilitates insect avoidance and not thermoregulatory gains. While the duration and spatial extent of snow declines globally as the climate warms, its diminishing availability is likely to have substantive impacts to populations given a general pattern of associations between insects and temperatures at high elevations and latitudes. Next, I evaluate changes in spatial use relative to high temperatures and the influence of snow on resource selection. While thermal challenges to persistence are well evidenced through historical extirpations, attention to near-term shifts in resource use and snow as a driver of summer resource selection remains under-investigated. I found strong shifts in resource selection during periods of high temperature, with increased selection for cooler habitats, little effect from snow, and evidence of ecological tradeoffs in avoidance of heat. These results point to possible demographic consequences of changing behavior and illustrate the importance of proactive consideration of changing patterns of use in management policies. Finally, I evaluate the importance of climate refugia and human translocation for the applied conservation of biodiversity. Despite a long history of relocating wildlife, translocations outside native ranges have rarely been conducted for conservation and populations introduced beyond their native ranges have seldom contributed to in situ species conservation within native ranges. Herein, I identify three cases of introductions to climate refugia and highlight the untapped conservation value of existing populations outside of native ranges. I report species in these refugia offer not only a reservoir for reintroductions but also a buffer against temperature-driven distributional change and may prove invaluable in stymieing current and future loss of biodiversity under continued climate challenges. In concert, this dissertation addresses physiological and geographical consequences of warming climes for cold-adapted species, identifies the need for proactive conservation, and highlights one avenue through which meaningful conservation benefits may be achieved.Item Open Access Logjam attenuation of annual sediment waves in eolian-fluvial environments, North Park, Colorado(Colorado State University. Libraries, 2020) Grabowski, Julia, author; Wohl, Ellen, advisor; McGrath, Daniel, committee member; Morrison, Ryan, committee memberSediment waves, a term that describes the fluvial transport of a discrete sediment influx, have long been studied in regard to channel response to infrequent, catastrophic events, such as mass movements or dam removal. However, few researchers have studied (1) the potential presence of sediment waves of annual or sub-annual scale in mixed eolian-fluvial geomorphic environments or (2) the role of large wood in sediment wave dispersal. This study addresses both topics through observations of North Sand Creek and East Sand Creek, which flow alongside the active sand dunes of North Sand Hills and East Sand Hills, respectively, in North Park, Colorado. The creeks experience similar seasonal, asynchronous cycles of eolian influx and fluvial transport, although North Sand Creek likely receives a greater volume of eolian sand due to intensive Off-Highway Vehicle (OHV) recreation on the North Sand Hills dunefield. Linear spectral unmixing of Landsat imagery from 1984-2019 is used to determine whether OHV recreation has resulted in vegetation loss, typically associated with elevated eolian flux, on North Sand Hills. Repeat photography and repeat measurement of terrace-like structures are used to determine whether each creek experiences a sediment wave, and repeat measurement of logjam sand wedge volume is used to examine changes in sand storage associated with logjams over time. Results indicate that North Sand Hills hast lost vegetative cover in areas not fenced-off to OHV users at a rate of ~800 m2/year, and that North Sand Creek experiences a highly translative sediment wave that is attenuated by logjams. East Sand Hills, on the other hand, has gained vegetative cover throughout the dunefield, and East Sand Creek does not experience a sediment wave. The sediment wave at North Sand Creek translates rapidly through the area of channel outside of the logjam backwater and translates more slowly through logjam backwater areas—principally through reduction in the length of logjam sand wedges, rather than reduction in depth.Item Open Access Low-cost data loggers for use with the conductivity mass balance method to estimate baseflow at snowmelt-dominated headwater streams in northwestern Colorado(Colorado State University. Libraries, 2021) Lidell, Amber Leigh, author; Sanford, William E., advisor; McGrath, Daniel, committee member; Covino, Tim, committee memberGroundwater contribution to streamflow (baseflow) in snowmelt-dominated headwater streams, particularly following the snowmelt peak, is crucial for sustaining late season flow necessary for maintaining instream functions and fluvial ecosystems. Quantification of baseflow following snowmelt helps managers to determine the potential impacts of climate variability or management activities on streamflow, among others. One method of estimating baseflow is the conductivity mass balance (CMB), which requires continuous measurement of stream discharge and specific conductance (SC). Most headwater streams lack this information, as commonly used data loggers to measure SC are costly, and headwater streams have extreme variations in accessibility, temperature, discharge, and sediment. The purpose of this study is to investigate a new means to log continuous SC data in snowmelt-dominated headwater streams where data collection options are limited by costs. The primary objectives include deploying, calibrating, and testing a new low-cost data logger to continuously measure SC, gauging ungauged streams to determine continuous discharge, and estimating baseflow. The low-cost Stream Temperature, Intermittency, and Conductivity (STIC) data loggers were developed by modifying Onset HOBO Pendant waterproof temperature and light data loggers. 17 of these loggers as well as three higher-cost SC loggers were deployed in 10 streams in the Medicine Bow-Routt National Forests in northwestern Colorado in 2017 and/or 2018. Nine headwater streams were gauged, and rating curves developed to determine continuous discharge. 15 STIC loggers were then calibrated to known SC standards, and of those, in-stream data from 11 were used with discharge data to estimate baseflow at seven sites. Regression outputs for these 11 are available in the supplementary files. The conductivity-discharge relationships of two streams did not meet the requirements of the CMB method. Baseflow was also estimated at two streams with data from the higher-cost SC loggers. During the 2018 post snowmelt-dominated period, the data from STIC and higher-cost loggers recorded data that were used to calculate a proportion of baseflow to total streamflow (baseflow index) within 0.7 percent of one another at North Fork of the Elk River. Data from two STIC loggers that were deployed at Roaring Fork of Slater Creek were used to estimate baseflow indexes within 0.2 percent of one another. The data recorded by STIC loggers worked well with discharge data to estimate baseflow at seven sites with the CMB method during the post snowmelt-dominated portion of each hydrograph, even after being subjected to extreme field conditions. Once calibration and data processing time were taken into account, seven STIC loggers can be used for approximately the same cost as one higher-cost SC logger. For the best STIC logger data acquisition, it is recommended to deploy two low-cost loggers at each site as was done for this study, in a location that is not likely to experience heavy deposition, extremely turbulent flows, or long-term frozen water (e.g., in a glide or near a pool-tail crest). It is also recommended to calibrate the STIC loggers prior to field deployment, as was not done in this study. The findings of this study encourage the possibility of collecting more continuous data at more snowmelt-dominated headwater streams due to the low cost of these STIC loggers. This in turn increases potential for more baseflow data to be acquired at these streams, to inform and support public land and water management decisions and add to the active area of research surrounding baseflow estimation at headwater streams.Item Open Access Neotectonic effects of glacial erosion and deglaciation on the Sangre de Cristo Mountains, southern Colorado(Colorado State University. Libraries, 2023) Hurtado, Cecilia, author; Gallen, Sean, advisor; Singleton, John, committee member; McGrath, Daniel, committee member; Denning, Scott, committee memberInterrelations between climate and tectonics are important to the development of active mountain belts, but rarely are there natural examples that lend themselves to studying the effects of climate on tectonics. The Sangre de Cristo Mountains in southern Colorado provide an optimal natural laboratory to explore the effects of alpine valley glaciation on surface uplift of the footwall and on the active extensional normal fault system in the northern Rio Grande rift. This region has experienced changes in surface loads associated with long-term glacial erosion and sedimentation over the course of the Quaternary, as well as shorter-term deglaciation after the Last Glacial Maximum. These changing loads correspond with stress changes that affect the flexural isostatic response of the lithosphere, and further act as clamping or unclamping stresses on the Sangre de Cristo fault that bounds the western margin of the mountain range. This work quantifies the masses and spatial distributions of these various loads and models the associated flexural isostatic response to estimate potential uplift and subsidence patterns in the study area that could be attributed to climate-driven mechanisms. The glacially-scoured footwall material was estimated by using remnants of the fluvial reaches downstream of glaciated drainage basins, reconstructing the paleofluvial topography, and subtracting it from the modern topography. The quantification of the deposited sediment in the San Luis Basin was measured from an interpolated surface tethered by existing drill cores, geophysical data, and geologic maps. Lastly, the glacial extents and thicknesses were constructed using a simple numerical modeling tool, GlaRe, constrained by preserved depositional and erosional evidence of glaciers. Isostatic responses were calculated using a flexure model with two effective elastic thickness (Te) values, 2 km and 5 km, and stress changes on faults at depth were calculated using an analytical line load model. The results estimate ~29 m of footwall uplift and ~47 m of subsidence in the hanging wall for a realistic Te of 5 km, and footwall uplift of ~48 m and a hanging wall subsidence of ~80 m for an independently calibrated Te of 2 km. Importantly, while topographic reconstructions indicate an ~50 m reduction in mean footwall elevations, isostatic rebound pushes mountain peaks upward by tens of meters. Footwall uplift due to deglaciation has a response of 4 m and 6 m, for a Te of 5 km and a Te of 2 km, respectively. The Sangre de Cristo fault trace was mapped to quantify the offset of fault scarps on Quaternary alluvial fans to determine the spatial and temporal patterns of offset along-strike of the fault. Fault offset magnitudes correlate with glacial domains, and fault slip rates correlate with the post-glacial spatial pattern of isostatic uplift, indicating an unambiguous link between deglaciation and elevated fault activity. This work demonstrates that (1) differential glacial erosion reduces mean footwall elevations, but the associated isostatic response drives surface uplift of mountain peaks, and (2) seismicity along normal faults could be amplified by load changes associated with climate-driven mechanisms, which will become increasingly important as we continue in a period of anthropogenic warming and deglaciation.Item Open Access Prioritization of beaver (Castor canadensis) reintroduction sites within semi-arid grassland rivers in the Great Plains(Colorado State University. Libraries, 2020) Kornse, Zachary, author; Wohl, Ellen, advisor; McGrath, Daniel, committee member; Morrison, Ryan, committee memberRiver restoration has become more of a concern with human influence on natural systems on the rise. Beaver provide a relatively inexpensive and natural opportunity to restore rivers to a pre-settlement state. Quantitative models can be used to better understand where beaver reintroduction should occur to maximize the odds of a reintroduced beaver population establishing an ideal habitat to thrive in. The Beaver Restoration Assessment Tool (BRAT) is a quantitative model that uses elevation, hydrology, and vegetation inputs to estimate the carrying capacity of beaver. The primary objective of this project is to develop baseline data that can inform river restoration of the Dale Creek watershed on Old Elk Ranch, a northern tributary to the Poudre River in Northern Colorado, although the methods used in this study are broadly applicable to other watersheds. This objective was addressed during two phases of work – the channel and riparian condition assessment during summer 2018 and the assessment of historic and contemporary potential beaver habitat using BRAT and field surveys during summer 2019. Through the utilization of BRAT, survey mapping, and remote sensing, I was further able to determine the best methods for estimating potential beaver population density, as well as the accuracy of the BRAT results relative to the field survey results. Remote sensing provides a unique opportunity to increase the accuracy of BRAT through image classification and analysis. A national vegetation dataset produced by LANDFIRE, with a spatial resolution of 10m, is not as spatially accurate as vegetation datasets derived though supervised classification of NAIP imagery with a 1m spatial resolution. Due to its coarser spatial resolution and being a product of generalized models and field data, LANDFIRE data missed important details in vegetation, such as riparian willows along valley bottoms and variabilities within the floodplain that are crucial for beaver survival. Furthermore, this increase in vegetation accuracy led to increasing the accuracy of BRAT predictions for beaver carrying capacity relative to ground-based mapping of past beaver occupation, allowing for better assessment of where beaver should be reintroduced. Historical BRAT estimates revealed that zero and 1st order channels had the highest carrying capacity of dams historically, accounting for 56% of reaches capable of the highest BRAT classification (15+ dams/km). According to the field survey and historical vs contemporary BRAT estimates, carrying capacity has been greatly reduced post human settlement, primarily in zero and 1st order channel valleys where cattle were introduced. The 2018 condition assessment confirmed that while riparian vegetation was healthiest in higher-order channels, zero and 1st order channels were heavily browsed by cattle, deer, and elk. Based on the distribution of riparian vegetation health, and carrying capacity estimates from BRAT and field surveys, stream restoration would be most effective on 0th and 1st order streams.Item Open Access Snowfall-driven topographic evolution: impacts on snow distribution patterns(Colorado State University. Libraries, 2023) Olsen-Mikitowicz, Alexander Richard, author; Fassnacht, Steven, advisor; McGrath, Daniel, committee member; Leisz, Stephen, committee memberThis study develops a scalable meteorologically independent snow accumulation model to better estimate snowpack depth using an enhanced representation of actual processes. Current snow accumulation models incorporate bare or snow-free surface properties derived from elevation, aspect, vegetation, and prevailing wind characteristics to determine the drivers of snow distribution yet neglect to consider how subsequent snowfalls can reshape the initial terrain conditions. We hypothesize that a snow depth model that accumulates snowfall while accounting for the antecedent snow-affected surface characteristics is more representative of natural processes and will therefore yield more accurate depth estimates than models that reference a snow-free topographic surface. To address this premise, the research explores (1) conducting a sensitivity analysis to evaluate the behavior of both models, (2) determining the differences between the two snow accumulation modeling approaches, and (3) assessing each model's performance in different location, scale, and temporal resolution conditions to determine their resiliency and transferability. Terrestrial LiDAR was employed at two field sites following snow deposition events and captured a range of spatial extents and resolutions. The Upper Piceance Creek (UPC) site near Meeker, CO covered approximately 10 m2 at centimeter resolution; the Izas Experimental Catchment in the Spanish Pyrenees covered 1 km2 at meter resolution. A regression tree machine learning model was utilized to estimate snow depth based on 14 topographic features. This process engaged in two mechanisms: 1. Static method, where snow depth (dst) determined from the bare earth digital terrain model (ds0) was estimated with snow-free topographic features and 2. Dynamic method, where snow depth (dst) determined from the previous snow surface height (dst-1) was estimated with the dst-1 snowfall affected surface. The analyses found that the models were resilient to changes in training allocations under a random sampling method, but sensitive to both the prevailing wind direction used for feature creation and the overall resolution used to represent surface features. The primary difference between the static and dynamic models for snow depth estimates was the number of features used and their relative importance. The static method had a higher overall median importance and relied mainly on Directional Relief and Relative Topographic Position for snow depth estimates, while the dynamic method displayed lower overall median importance but utilized more surface features over a single accumulation season. The dynamic method outperformed the static method at UPC by approximately 0.07 in a Nash-Sutcliffe efficiency comparison, and only 0.01 at Izas Experimental Catchment suggesting issues with process-scale representation of snow accumulation at the Izas site.Item Open Access The contribution of clouds to global surface temperature variability on monthly to decadal timescales(Colorado State University. Libraries, 2022) Boehm, Chloe, author; Thompson, David W. J., advisor; Randall, David, committee member; McGrath, Daniel, committee memberCloud radiative effects (CREs) have well documented impacts on the mean climate, and have recently been found to play a key role in climate variability in the tropics. This thesis expands on previous work to probe the role of CREs on extratropical surface temperature variability. The impact of CREs on climate variability is isolated using the 'cloud-locking' method run on the Max Planck Earth System Model. This method involves comparing the output from two climate simulations: one in which clouds are coupled to the atmospheric circulation, and another in which clouds are prescribed and thus decoupled from the flow. Results show that coupling between CREs and the atmospheric circulation leads to widespread increases in extratropical surface temperature variability, particularly over the North Atlantic and North Pacific. This work then explores on what timescales surface temperature variability is increased. In general, CREs play an increasingly large role in surface temperature variability at increasingly long timescales. Importantly, cloud-circulation coupling leads to enhanced decadal temperature variability of ~25–45% over most of the Northern Hemisphere oceans and ~10–15% over most of the land areas. Finally, using a simple expression for temperature variance in terms of the surface energy balance, the mechanisms driving these variability changes are identified. This variability enhancement derives from 'reddening' of surface temperature variability by cloud shortwave radiative effects. These results demonstrate the dominant effect that cloud-circulation coupling has on interannual and decadal temperature variability across much of the globe. This work has implications for the interpretation of observed decadal variability, and for the importance of cloud-circulation coupling in climate model simulations.Item Open Access The effects of land surface-atmosphere interactions within two convective storm regimes(Colorado State University. Libraries, 2024) Ascher, Benjamin D., author; van den Heever, Susan C., advisor; Schumacher, Russ, committee member; McGrath, Daniel, committee memberConvective storms, which are driven in part by atmospheric thermodynamic instability, come in a range of shapes and sizes and bring a variety of impacts both at the surface and throughout the atmosphere. Often these storms initiate as a result of lifting within the Planetary Boundary Layer (PBL), the behavior of which is strongly affected by the characteristics of the land surface below them. To examine the effects of land surface properties on convective storm behavior and impacts, I have conducted two high-resolution mesoscale modeling studies. The first study examined the impact of Lake Huron on convective lake-effect snow over Lake Erie, while the second analyzed the effects of heterogeneous vegetation cover on deep convection in an idealized coastal environment. Our findings in the first study revealed that Lake Huron initiates lake-effect snow bands which persist over land between Lake Huron and Lake Erie and then reintensify after moving over Lake Erie. The persistent band "kickstarts" convection over Lake Erie and increases snowfall over and downwind of Lake Erie compared to when Lake Huron is not present. I also found that areas of snow-free land can act as a "brown lake" and initiate lake effect-like convection on their own. An area of snow-free land upwind of Lake Erie fulfilled a similar role to Lake Huron in enhancing convection and snowfall downwind of Lake Erie. Such findings may have important implications for improved short-term forecasting of the location and intensity of heavy snowfall. The results in our second study indicated that heterogeneous land surfaces enhance convective storm activity over certain vegetation types and suppress it over others. In particular, I found an increase in precipitation over forests surrounded by pasture lands and suburban regions, while the precipitation over the pasture and suburban regions is suppressed. I also discovered that circulations induced by these heterogeneous land surfaces appear to be more important to the location and timing of convection initiation than a sea breeze which forms in the simulations. Finally, I concluded that cold pools produced by convective storms reinforce the land surface-induced circulations, thereby allowing these circulations to collide in the center of the forested region, where they initiate intense convection which subsequently produces heavy rainfall.Item Open Access Tidally induced seismicity at the grounded margins of the Ross Ice Shelf, Antarctica(Colorado State University. Libraries, 2020) Cole, Hank M., author; Aster, Richard C., advisor; McGrath, Daniel, committee member; Cheney, Margaret, committee member; Benz, Harley, committee memberRepeating swarms of local icequakes were recorded by broadband seismograpghs deployed near the grounding line of the Ross Ice Shelf, Antarctica from late 2014 to early 2017. Swarms commonly persist for over six hours and contain thousands of events. Most swarms are induced or enhanced by tidal forcing. The number of events and event amplitudes in a swarm is most correlated with the modeled tide range. Some swarms only occur during cold periods of the austral winter. Icequakes are cataloged using a cross-correlation detector after building a template library from clustered STA/LTA picks and epicenters are estimated for high quality events. Events can be classified into four broad categories. The first event type is the most common (>95% of events) and occurs in diurnal swarms at all times of year. This type of event is interpreted to be sourced by propagation of near surface crevasses due to enhanced tensile stress from downward flexure of the ice shelf during falling tide. The second type of event has similar waveforms but occurs at the crest of large spring tides and appears to have an englacial or basal source. The third type of event is likely sourced from within the firn, possibly related to densification. It is also observed at stations in the ice shelf interior, but appears enhanced by tides at stations near the grounding line. The fourth type of event is only observed at a station on the Steershead Ice Rise. These are sweeping harmonic tremors lasting up to 8 s that start at low frequency and then tail upwards into an impulse like signal. This work characterizes these icequake types and their correlation to tidal and environmental forcing. It also details a single station event location scheme that is to used to further interpret events by finding their back azimuth with a polarization analysis and estimate their source-receiver distance with two methods. These observations provide insight into the deformation and brittle fracture at the grounded margins of the Ross Ice Shelf.Item Open Access Variable fresh snow albedo: how snowpack and sub-nivean properties influence fresh snow reflectance(Colorado State University. Libraries, 2021) Reimanis, Danielle C., author; Fassnacht, Steven, advisor; Butters, Gregory, committee member; McGrath, Daniel, committee memberThe understanding of albedo, or ratio of outgoing to incoming shortwave radiation, is necessary for modeling the melt characteristics of a snowpack in snow-dominated areas. The timing and supply of meltwater downstream is influenced by the energy balance, and albedo is used in those calculations. Current snow albedo models range from simple models that only reset albedo with new snowfall to complex models that are not feasible for most applications. We present a variable fresh snow model that enhances a simple albedo model, initially created by the U.S. Army Corps of Engineers, and used extensively in the Canadian LAnd Surface Scheme (CLASS). The new approach considers conditions prior to and during a snowfall event to improve fresh snow albedo estimates, instead of resetting to a static value; it also considers differences in the albedo decay rate.Hourly shortwave radiation (incoming and outgoing), snow depth, temperature, and other meteorological data from two stations at the Senator Beck Basin in the San Juan Mountains of Southwest, Colorado were used for the period from 2005 to 2014. We evaluated changes in albedo of a high-elevation seasonal snowpack during fresh snow events and apply a set of multivariate regressions to recreate values of broadband albedo. The variable fresh snow albedo model approaches the Visible and Near-Shortwave Infrared portion of the electromagnetic spectrum differently and groups values by temperature. The model needs few inputs, specifically measurements of depth and temperature, an estimation of ground albedo, and for increased accuracy, a quantification of the number of aeolian dust deposition events on the snowpack every year. This variable fresh snow model showed higher accuracy in albedo values, both of fresh and decayed snow (R2 of 0.77 and Nash Sutcliffe Efficiency, NSE of 0.75) than of CLASS (R2 of 0.67 and NSE of 0.62). When isolating fresh snow events, the variable fresh snow albedo model was much more accurate than the single-reset albedo provided by CLASS but still had a weak correlation to measured values (R2 of 0.38). The variable fresh snow albedo model especially outperformed CLASS during the melt period, with ~24% more accurate absorption values to measured values than CLASS. Since fresh snow albedo is primarily weighted by albedo from the timestep before, we suggest this model also be used to correct erroneous values of albedo given incorrect sensor measurements, such as due to snow accumulation on the upward looking shortwave radiation sensor (pyranometer).