Browsing by Author "Kampf, Stephanie K., committee member"
Now showing 1 - 15 of 15
Results Per Page
Sort Options
Item Open Access A method to downscale soil moisture to fine-resolutions using topographic, vegetation, and soil data(Colorado State University. Libraries, 2014) Ranney, Kayla J., author; Niemann, Jeffrey D., advisor; Green, Timothy R., committee member; Kampf, Stephanie K., committee memberVarious remote-sensing and ground-based sensor methods are available to estimate soil moisture over large regions with spatial resolutions greater than 500 m. However, applications such as water management and agricultural production require finer resolutions (10 - 100 m grid cells). To reach such resolutions, soil moisture must be downscaled using supplemental data. Several downscaling methods use only topographic data, but vegetation and soil characteristics also affect fine-scale soil moisture variations. In this thesis, a downscaling model that uses topographic, vegetation, and soil data is presented, which is called the Equilibrium Moisture from Topography, Vegetation, and Soil (EMT+VS) model. The EMT+VS model assumes a steady-state water balance involving: infiltration, deep drainage, lateral flow, and evapotranspiration. The magnitude of each process at each location is inferred from topographic, vegetation, and soil characteristics. To evaluate the model, it is applied to three catchments with extensive soil moisture and topographic data and compared to an Empirical Orthogonal Function (EOF) downscaling method. The primary test catchment is Cache la Poudre, which has variable vegetation cover. Extensive vegetation and soil data were available for this catchment. Additional testing is performed using the Tarrawarra and Nerrigundah catchments where vegetation is relatively homogeneous and limited soil data are available for interpolation. For Cache la Poudre, the estimated soil moisture patterns improve substantially when the vegetation and soil data are used in addition to topographic data, and the performance is similar for the EMT+VS and EOF models. Adding spatially-interpolated soil data to the topographic data at Tarrawarra and Nerrigundah decreases model performance and results in worse performance than the EOF method, in which the soil data are not highly weighted. These results suggest that the soil data must have greater spatial detail to be useful to the EMT+VS model.Item Open Access Bulking coefficients of aerated flow during wave overtopping simulation on protected land-side slopes(Colorado State University. Libraries, 2016) Scholl, Bryan N., author; Thornton, Christopher I., advisor; Abt, Steven R., advisor; Hughes, Steven A., committee member; Venayagamoorthy, Subhas K., committee member; Kampf, Stephanie K., committee memberPost hurricane Katrina there has been more interest in erosion on the landward side of levees resulting from wave overtopping during storm events. The development of wave overtopping simulators has enabled more rigorous evaluation of levee armoring alternatives under controlled conditions similar to those on levees. Steady state overtopping studies have demonstrated a reduction in shear stress due to air entrainment in the flow. There has not been an evaluation of air entrainment during wave overtopping simulation. For this reason, a study was conducted to quantify flow bulking occurring during wave overtopping simulation. Testing was conducted at the Hydraulics Laboratory at Colorado State University at the Engineering Research Center using a wave overtopping simulator. The simulated levee was 6 ft wide. Levee geometry in the direction of flow was a 13.2 ft. horizontal crest, 30.5 ft levee face with 3:1 (horizontal:vertical) slope and 12.2 ft berm with 25:1 slope. Un-bulked flow thickness was measured with “surfboards” which hydroplane along the surface of flow. Bulked flow thicknesses were measured using visual observations of maximum flow thickness on eight staff gages along the wall of the simulated levee. Wave volumes ranged from 20 ft3/ft to 175 ft3/ft. Conservation of mass and testing repeatability is demonstrated. Bulking values range from zero for the smallest wave volumes to over 100% for the largest wave volumes. An empirical model is developed to estimate bulking on the 3:1 levee slope. A comparison is made to steady state flows with similar air entrainment. The effect of bulking on shear stress is a potential decrease in shear stress over 50% relative to un-bulked flow thickness. A method to incorporate wave overtopping bulking into design is proposed using a cumulative work approach.Item Open Access Climatic and hydrologic processes leading to recent wetland losses in Yellowstone National Park, USA(Colorado State University. Libraries, 2012) Schook, Derek M., author; Cooper, David J., advisor; Ronayne, Michael J., committee member; Kampf, Stephanie K., committee memberWetlands provide vital habitat within functioning environments and act as landscape indicators by integrating catchment-scale hydrologic processes. Wetland drying during the past few decades in Yellowstone National Park's Northern Range has caused concern among National Park managers and the public at large. My research was initiated to develop an understanding of the processes controlling wetland water levels and contributing to wetland decline in the Northern Range. To do this I integrated analyses of hydrology, climate, soils, and vegetation. In 2009 I selected 24 study wetlands and instrumented each with an average of five shallow groundwater monitoring well-and-piezometer nests. To quantify historic wetland area I mapped hydric soils, analyzed aerial photographs, and identified geomorphic indicators of higher water. Vegetation was sampled to characterize wetlands and plant-water relationships, and I also conducted a soil seed bank study. The Trumpeter Lake focal site revealed groundwater changes through time and was used to identify the timescale on which an important wetland varies. Climate data indicated that warming and drying occurred during the 20th century, but that this pattern was within the natural range of variation for the study region during the past 800 years. Hydrologic data revealed that study sites included locations of groundwater discharge, recharge, and flow-through as well as water perched above the regional water table. Hydrologic regimes were classified using a shape-magnitude framework and seven wetland classes were characterized. Wetland classes exhibited variable hydrologic permanence within and between the two study summers. Aerial photographs and hydric soil delineation both confirmed formerly greater wetland abundance. These changes were linked to the wetland classes and the presence or absence of surface water outlets. Wetland plant species inhabited areas of distinct water table depth and variation, and can be used to infer subsurface hydrologic regime in the absence of extensive monitoring well networks. Continued monitoring of these wetland basins and their watersheds is critical to expanding our understanding of the processes supporting Northern Range wetlands and allowing us to better manage these valuable habitats.Item Open Access Downscaling soil moisture over regions that include multiple coarse-resolution grid cells(Colorado State University. Libraries, 2016) Hoehn, Dylan C., author; Niemann, Jeffrey D., advisor; Green, Timothy R., committee member; Kampf, Stephanie K., committee memberMany applications require soil moisture estimates over large spatial extents (30-300 km) and at fine-resolutions (10-30 m). Remote-sensing methods can provide soil moisture estimates over very large spatial extents (continental to global) at coarse resolutions (10-40 km), but their output must be downscaled to reach fine resolutions. When large spatial extents are considered, the downscaling procedure must consider multiple coarse-resolution grid cells, yet little attention has been given to the treatment of multiple grid cells. The objective of this paper is to compare the performance of different methods for addressing multiple coarse grid cells. To accomplish this goal, the Equilibrium Moisture from Topography, Vegetation, and Soil (EMT+VS) downscaling model is generalized to accept multiple coarse grid cells, and two methods for their treatment are implemented and compared. The first method (fixed window) is a direct extension of the original EMT+VS model and downscales each coarse grid cell independently. The second method (shifting window) replaces the coarse grid cell values with values that are calculated from windows that are centered on each fine grid cell. The window values are weighted averages of the coarse grid values within the window extent, and three weighting methods are considered (box, disk, and Gaussian). The methods are applied to three small catchments with detailed soil moisture observations and one large region. The fixed window typically provides more accurate estimates of soil moisture than the shifting window, but it produces abrupt changes in soil moisture at the coarse grid boundaries, which may be problematic for some applications. The three weighting methods produce similar results.Item Open Access Erosion mapping and sediment yield of the Kabul River Basin, Afghanistan(Colorado State University. Libraries, 2013) Sahaar, Ahmad Shukran, author; Julien, Pierre Y., advisor; Arabi, Mazdak, committee member; Kampf, Stephanie K., committee memberSoil erosion by water is a serious issue in Afghanistan. Due to the geographic landscape, soil and climatic conditions, and the latest deforestation activities, there has been intensive soil erosion which has resulted in prolonged and great impact on social and economic development of the region. In fact, recent environmental assessment shows that decades of war and continuous drought have resulted in widespread environmental degradation throughout the country; therefore, mapping of soil erosion at the basin scale is urgently needed. The Kabul River Basin was selected for the purpose of erosion and sedimentation modeling due to its great socio-economic impact. The main objectives of this study include: (1) calculations of the annual average soil loss rates at the basin level; (2) spatial distribution of soil erosion rates at the basin level; (3) predictions of deforestation effects on sediment losses under different land cover scenarios at the watershed level; and (4) calculation of sediment delivery ratios based on soil erosion rates, and sediment yields at the sub-watershed levels in the basin. This study uses the Revised Universal Soil Loss Equation (RUSLE) model combined with Geographic Information System (GIS) techniques to analyze the gross soil loss rates and the spatial distribution of soil loss rates under different land uses. Digital elevation model (DEM), average annual precipitation data, land cover map and soil type map were used to define the parameters of the RUSLE model. The annual average soil loss rate of the Kabul River Basin was estimated to be 19 tons/acre/year (4748 tons/km2/year), and the gross mean annual soil loss rate found to be 47 million tons/year. By producing 57 % of the total annual average soil loss, rangelands were the primary contributor to the basin. In case of the spatial distribution of erosion rates at the Kabul River Basin, the relationship between probability and annual average soil loss rates were analyzed. The analysis indicated that up to sixty percent of the mean annual soil loss rates are in the range of tolerable soil loss rate (0 - 5 tons/acre/year). Moreover, northern part of the basin is prone to more extensive erosion than the southern part. The study predicted that if the forest region of the Kunar watershed is completely reduced to barren lands, the watershed will produce five times more sediment than the estimated soil loss rate from 1993's UN-FAO land cover map. The annual average soil loss rate in this watershed was about 29 tons/acre/year but it will increase to 149 tons/acre/year as deforestation continues to take place in the watershed. The range of sediment delivery ratios for the basin's rivers is 2.5 -10.8 %. Based on this evaluation, the sediment delivery ratio for the sediment gauging stations in the basin are in the similar range of predicted values by the methods of Boyce, Renfro, Williams and Maner.Item Open Access Precipitation and temperature changes and their effect on groundwater along the Kona coast of Hawai'i(Colorado State University. Libraries, 2015) Stevenson, Sharla Ann, author; Fassnacht, Steven, advisor; Kampf, Stephanie K., committee member; Butters, Gregory, committee memberWater resources are an important part of the Hawaiian cultural tradition, and a shift to a warmer, dryer climate may initiate physical and biological changes that would inhibit the practice of Native Hawaiian cultural traditions by altering the coastal ecosystem resources such as those found within Kaloko-Honokōhau National Historical Park. The high degree of spatial heterogeneity and numerous microclimates on the Island of Hawai'i motivated an in-depth analysis of changes in precipitation and temperature occurring during the time since the park was established in 1978 up to the year 2010 at stations located within the regional recharge area for the Kona aquifer system. The potential long-term implications of changes in climate to groundwater recharge were also modeled using stochastic techniques. A statistical analysis was conducted on annual, winter, and summer precipitation and minimum and maximum temperature climate records using the Mann-Kendall test to detect the presence of a monotonic increasing or decreasing trend at significance levels of alpha = 0.1, 0.05, 0.01, and 0.001. The similarities and differences between station records were further evaluated by a double mass analysis of the same precipitation datasets. The changes identified during trend analysis were used to create synthetic realizations of temperature and rainfall patterns 50 years into the future using stochastic modeling techniques. The future realizations were analyzed to evaluate changes in net precipitation and the potential effect on groundwater recharge. Within the Kona aquifer recharge area there is evidence of diverse changes in rainfall that have taken place over recent decades. 13 out of 15 stations evaluated for changes in rainfall have decreasing trends during the 1978 to 2010 time period and over their entire observation record. Decreases in annual rainfall range from 30mm to 250mm per decade with the majority of declines occurring in the summer season. Almost half of the stations had significant changes in rainfall during the summer season, but none of the changes in winter rainfall were significant. The trends displayed in both rainfall and temperature when modeled 50 years into the future indicate declines in net precipitation ranging from 6 to 48% compared to the modeled stationary 50 year mean. All of the modeled scenarios indicated a decline in the number of days with rainfall for all of the locations with the decline resulting in four locations having a season with no rainfall at all. Large declines in modeled net precipitation such as these would affect the overall amount of recharge to the regional aquifer. In an island ecosystem, the constant pressure of saltwater intrusion and the input of freshwater recharge creates a delicate balance of fresh and saline water underground. Any change in net precipitation that affects recharge could disrupt that delicate balance allowing increased saltwater intrusion along the coastline and within the Park.Item Open Access Quantifying lawn irrigation contributions to semi-arid, urban stream baseflow with water-stable isotopes(Colorado State University. Libraries, 2020) Fillo, Noelle K., author; Bhaskar, Aditi S., advisor; Bailey, Ryan T., committee member; Kampf, Stephanie K., committee memberIn semi-arid cities, urbanization can lead to elevated baseflow during summer months. One potential source for the additional water is lawn irrigation. We sought to quantify the presence of lawn irrigation in Denver's summertime baseflow using water-stable isotope (δ18O and δ2H) analysis of surface water, tap water, and precipitation. If lawn irrigation contributed significantly to baseflow, we predicted the isotopic composition of Denver's urban streams would more closely resemble the local tap water than precipitation or streamflow from nearby grassland watersheds. We expected the tap water to be distinctive due to local water providers importing much of their source water from high elevations. Thirteen urban streams and two grassland streams were selected for sampling. The thirteen urban watersheds ranged from 3.9 km2 - 63.3 km2 in drainage area and 22% - 44% in imperviousness. The two grassland watersheds had drainage areas of 3.7 km2 and 7.5 km2 as well as 1% and 5% imperviousness. None of the streams had high-elevation headwaters or wastewater effluent, and the grassland streams did not receive irrigation. Tap water was sampled from five local water provider service areas. Wide spatial and temporal variation in isotopic composition was observed within the stream, tap and precipitation samples. Comparison of samples between nearby watersheds revealed that proximity did not imply similar isotopic values. Streamflow analysis focusing on summer 2019 revealed that the grassland watersheds flowed for 60% of the summer while urban watersheds flowed for 90% - 100% of the summer. A two end-member isotope mixing model using tap and precipitation end-members estimated that tap water contributed 61% - 97% of urban streamflow on specific days in late summer. After taking estimated contributions from infrastructure leakage into account, we conservatively determined the lawn irrigation return flows made up 4% - 75% of the modeled baseflow. Quantifying the contribution of lawn irrigation to urban baseflow will provide a basis for understanding how changes to lawn irrigation efficiency would affect water yield in the Denver metropolitan area.Item Embargo Recent and future Colorado water: snow drought, streamflow, and winter recreation(Colorado State University. Libraries, 2023) Pfohl, Anna K. D., author; Fassnacht, Steven R., advisor; Barnard, David M., committee member; Kampf, Stephanie K., committee member; Rasmussen, Kristen L., committee memberWater in the western United States is a crucial resource for ecosystems, the abiotic environment, and people (for industrial, agricultural, and residential purposes). A majority of this water originates in the seasonal snowpack in the mountains. The snowpack is responsible for maintaining the water supply, and changes to this system have broad and severe implications. Various metrics have been used to quantify these patterns when snow is less than normal, often referred to as a snow drought or a low snow year. In recent decades, the number of years with low snow have increased, and this will continue and intensify into the future. With observed decreases in long-term snow and modeled decreases for the future, high snow years become more critical to support the water supply. Beyond supplying water for downstream use, the seasonal snowpack also sustains the winter recreation industry, which is a large component of many local and state economies. The Weather Research and Forecasting Model (WRF) is a 4-km mesoscale model that can capture orography and convective processes over complex terrain. WRF includes two time periods: the control (CTL) based on historic conditions and the future under pseudo-global warming (PGW) conditions. This dataset was used to drive SnowModel (WRF-SM) to produce 100-m, daily snow water equivalent (SWE), total precipitation, solid precipitation, snowmelt, runoff, and air temperature. Using these datasets, this research examines past and future snow and streamflow in Colorado. We evaluated 1) common metrics and trends for snow drought; 2) used WRF data to drive the Ages hydrologic model to examine changes (snow, streamflow, and flow partitioning) in two high snow years; and 3) ski opportunities at nine different resorts. To evaluate methods of defining snow drought, we used SWE and winter precipitation data from Snow Telemetry stations and the WRF-SM dataset described above. Classifying drought with the ratio of SWE to winter precipitation resulted in drought occurrence for more than 50% of station-years from 1981 to 2020. Using percentiles of long-term peak SWE indicated that occurrence of low or very low years increased from 2001 to 2020 compared with the previous 20 years. Under PGW conditions, elevations between 1800 and 2400 m shifted drought classification towards low or very low, with higher elevations (3200 m and above) remaining relatively unchanged. To examine changes in snow, streamflow, and flow partitioning under a PGW scenario for two high snow years (2008 and 2011), we used Ages, a spatially distributed watershed model, in the Upper Blue River watershed in central Colorado. Changes in snow (snowmelt and solid precipitation) were greatest in magnitude at high elevations. Timing of peak streamflow shifted to nearly two months earlier under a PGW scenario. To examine ski opportunities, we developed metrics to quantify ski conditions. The number of opportunities for snowmaking in the future will decrease throughout the season, but especially in October and November. Ski days (snow depth greater than 50 cm) will decrease in early and late season and increase at lower elevations from January through March. Powder days (fresh depth greater than 15 cm and fresh density greater than 125 kg/m3) follow a similar pattern. Ski resorts at low elevations will generally be more susceptible to changes under a PGW scenario. Additionally, using a fine-resolution dataset allowed investigation of smaller study areas to understand the changes that are not captured with coarser resolutions.Item Open Access Response of native phreatophytes to changes in precipitation in the San Luis Valley, Colorado(Colorado State University. Libraries, 2010) Kray, Julie Ann, author; Cooper, David J., advisor; Kampf, Stephanie K., committee member; Knapp, Alan K., 1956-, committee member; Sanderson, John S., committee memberThroughout western North America, semiarid and arid basins are likely to experience changes in the timing and amount of precipitation due to global climate change, which may alter regional water budgets. These hydrologic changes may exacerbate water limitations on agriculture, municipalities, and ecosystems in arid regions. Thus, accurate estimates of groundwater outflow from native plant evapotranspiration (ETg) are increasingly critical to managing water resources in basins with large, shallow aquifers. Phreatophytes can contribute significantly to total groundwater outflow on a watershed scale. Some phreatophytes can also acquire soil water recharged by precipitation, which may reduce or supplement their groundwater use. As a result, groundwater use by phreatophyte communities may vary both spatially and temporally in response to seasonal or long-term changes in growing season precipitation. I conducted a two-year rainfall manipulation experiment in the San Luis Valley, Colorado to investigate the responses of four common native phreatophyte species to ambient, increased, and decreased summer monsoon rainfall. Volumetric soil water content was measured in experimental plots to evaluate rainfall treatment effectiveness. I measured xylem pressure potentials (Ψ) to assess the effects of altered precipitation on plant water relations, and compared stable oxygen isotope signatures (δ18O) of plant xylem water to surface (0-15 cm) and sub-surface (15-30 cm) soil layers and groundwater to identify plant water acquisition patterns. The response of plant water relations and water acquisition patterns to changes in surface soil water availability differed by species. A decrease in rainfall had a larger influence on Ψ in the grasses Sporobolus airoides and Distichlis spicata than the more deeply rooted shrubs Sarcobatus vermiculatus and Ericameria nauseosa. S. airoides, D. spicata and S. vermiculatus had significantly lower Ψ when rainfall was naturally low or experimentally reduced, while Ψ of E. nauseosa did not respond to natural or experimental differences in available soil water. Plant xylem water δ18O indicated that S. airoides and D. spicata are almost entirely dependent on precipitation-recharged soil water, while E. nauseosa is almost entirely groundwater-dependent throughout the growing season. S. vermiculatus used groundwater during dry periods, but incorporated more precipitation from upper soil layers after heavy monsoon rainfall. These results suggest that changes in growing season precipitation are more likely to affect S. airoides and D. spicata, while E. nauseosa and to a lesser extent, S. vermiculatus, may be more affected by a decline in water table depth. Persistent changes in precipitation patterns may cause a shift in plant community composition that would alter basin-scale groundwater use by native plants. Results of this work could inform models for managing groundwater in the San Luis Valley, and may have implications for other water-limited regions.Item Open Access Spatial and temporal channel changes across the watershed scale following wildfire and floods(Colorado State University. Libraries, 2018) Brogan, Daniel Joseph, author; Nelson, Peter A., advisor; Kampf, Stephanie K., committee member; MacDonald, Lee H., committee member; Niemann, Jeffrey D., committee memberFires and floods are important drivers of geomorphic change. The hydrologic and sedimentologic effects of fires have been relatively well studied at the hillslope scale, but we still lack the ability to accurately quantify and predict post-fire flooding and geomorphic changes at larger scales. This lack of understanding stems primarily from two reasons. First, there is generally limited availability of repeat high-resolution topography following fires, and this limits our ability to quantify and explain changes throughout a given channel network. Second and more fundamentally, one cannot simply scale up hillslope processes to the watershed scale, or vice-versa. Since global warming is leading to more wildfires and a higher likelihood of extreme precipitation, understanding downstream flooding and sedimentation is more critical than ever for safeguarding downstream landowners, water users, and aquatic biota. This dissertation investigates these shortcomings by documenting post-fire channel changes across watershed scales and how extreme floods can alter the more typical post-fire geomorphic response. I focus on two ~15 km2 watersheds, Skin Gulch (SG) and Hill Gulch (HG), that burned in the 2012 High Park Fire, Fort Collins, Colorado, U.S.A. Over the subsequent four years I used repeat surveys of 10-11 cross sections and longitudinal profiles along the lower channel network of each watershed, and five sequential airborne laser scanning (ALS) surveys, to quantify erosion and deposition. SG was first subjected to a high-intensity convective storm just days after the fire was contained; the resulting flood caused an exceptionally large peak flow, and extensive downstream deposition of cobbles, boulders and woody debris. Fifteen months later SG and HG experienced catastrophic stripping and bed coarsening due to an unusually rare and widespread mesoscale storm, with much greater changes in SG. These events and the data used to document their effects set up the basis of three separate, yet interdependent comparisons. First, I compare and contrast the peak flows and the effects of the two distinctly different flood disturbances in SG: the short-term peak flow and substantial deposition caused by the convective flood immediately after burning; and the widespread channel and valley bottom erosion caused by the mesoscale flood. Peak flows were estimated using three independent techniques: 1) slope-area method, 2) critical flow, and 3) 2D hydrodynamic modeling. The peak flow estimates for the 2013 flood had a higher relative uncertainty and this stemmed from whether I used pre- or post-flood channel topography. The results document the extent to which a high and moderate severity wildfire can greatly increase peak flows and alter channel morphology, illustrate how indirect peak flow estimates have larger errors than is generally assumed, and indicate that the magnitude of post-fire floods and geomorphic change can be affected by the timing, magnitude, duration, and sequence of rainstorms. Second, I use the repeat surveys of the cross sections and longitudinal profiles to quantify the channel response to the 2012 wildfire, summer thunderstorms, spring snowmelt, and the mesoscale flood in both SG and HG. The varying response between the two watersheds during the mesoscale flood necessitated further investigation. Discussions with a local landowner indicated that a flood in 1976 caused tremendous channel erosion and widening in the lower portion of HG. Geomorphic changes in HG after the fire and the mesoscale flood were much smaller than in SG, and this can be attributed to: greater post-fire, pre-mesoscale flood deposition in SG; reduced sensitivity in HG as a result of the large erosional flood in 1976; and the spatial distribution of burn severity leading to a lower peak flow in HG from the mesoscale flood. These results suggest that fires can trigger significant and dynamic channel changes over sub-decadal timescales, but unusually long or intense rainstorms can cause larger and more persistent watershed-scale changes regardless of whether a catchment has recently burned. I propose a state-and-transition conceptual model to relate landscape sensitivity to geomorphic changes according to its history of fires and floods. Third, I use the repeat ALS data to quantify spatial and temporal patterns of erosion and deposition throughout the channel networks of SG and HG. These volumes of change are related to valley and basin morphology, precipitation amounts and intensities, and burn severity. The results suggest that the amount and location of stored sediment in the valleys is critical for evaluating potential locations of erosion and deposition. Morphometric characteristics, when combined with burn severity and a specified storm, can indicate the relative likelihood and locations of post-fire erosion and deposition risks. Taken together, this body of work demonstrates: 1) how the timing and sequence of different disturbances affect the relative sensitivity of watersheds to downstream channel changes; 2) that the effects of extreme floods are longer lasting and more dominant than the effects of wildfires; and 3) that the amount and location of stored sediment in the valleys is critical for predicting potential geomorphic change. This information can help resource managers assess downstream risks and prioritize areas for post-fire hillslope rehabilitation treatments.Item Open Access Statistical modeling and computing for climate data(Colorado State University. Libraries, 2019) Hewitt, Joshua, author; Hoeting, Jennifer A., advisor; Cooley, Daniel S., committee member; Wang, Haonan, committee member; Kampf, Stephanie K., committee memberThe motivation for this thesis is to provide improved statistical models and approaches to statistical computing for analyzing climate patterns over short and long distances. In particular, information needs for water managers motivate my research. Statistical models and computing techniques exist in a careful balance because climate data are generated by physical processes that can yield computationally intractable statistical models. Simplified or approximate statistical models are often required for practical data analyses. Critically, model complexity is moderated as much by research needs and available data as it is by computational capabilities. I start by developing a weighted likelihood that improves estimates of high quantiles for extreme precipitation (i.e., return levels) from latent spatial extremes models. In my second project, I develop a geostatistical model that accounts for the influence of remotely observed spatial covariates. The model improves prediction of regional precipitation and related climate variables that are influenced by global-scale processes known as teleconnections. I make the model more accessible by providing an R package that includes visualization, estimation, prediction, and diagnostic tools. The models from my first two projects require estimating large numbers of latent effects, so their implementations rely on computationally efficient methods. My third project proposes a deterministic, quadrature-based computational approach for estimating hierarchical Bayesian models with many hyperparameters, including those from my first two projects. The deterministic method is easily parallelizable and can require substantially less computational effort than common stochastic alternatives, like Monte Carlo methods. Notably, my quadrature-based method can also improve the computational efficiency of other recent, fast, deterministic approaches for estimating hierarchical Bayesian models, such as the integrated nested Laplace approximation (INLA). I also make the quadrature-based method accessible through an R package that provides inference for user-specified hierarchical models. Throughout my thesis, I demonstrate how improved models, more efficient computational methods, and accessible software allow modeling of large, complex climate data.Item Open Access Stepwise nonparametric disaggregation for daily streamflow generation conditional on hydrologic and large-scale climatic signals(Colorado State University. Libraries, 2010) Molina Tabares, José Manuel, author; Ramírez, Jorge A., advisor; Salas, Jose D., advisor; Raff, David A., committee member; Kampf, Stephanie K., committee memberA stepwise nonparametric stochastic disaggregation framework to produce synthetic scenarios of daily streamflow conditional on volumes of spring runoff and large-scale ocean-atmosphere oscillations is presented. This thesis examines statistical links (i.e., teleconnections) between decadal/interannual climatic variations in the Pacific Ocean and hydrologic variability in US northwest region, and includes a spectral analysis of climate signals to detect coherences of their behavior in the frequency domain. We explore the use of such teleconnections of selected signals (e.g., north Pacific gyre oscillation, southern oscillation, and Pacific decadal oscillation indices) in the proposed data-driven framework by means of a cross-validation-based combinatorial approach with the aim of simulating improved streamflow sequences when compared with disaggregated series generated from flows alone. A nearest neighbor time series bootstrapping approach is integrated with principal component analysis to resample from the empirical multivariate distribution. A volume-dependent scaling transformation is implemented to guarantee the summability condition. The downscaling process includes a two-level cascade scheme: seasonal-to-monthly disaggregation first followed by monthly-to-daily disaggregation. Although the stepwise procedure may lead to a lack of preservation of the historical correlation between flows of the last day of a month and flows of the first day of the following month, we present a new and simple algorithm, based on nonparametric resampling, that overcomes this limitation. The downscaling framework presented here is parsimonious in parameters and model assumptions, does not generate negative values, and preserves very well the statistical characteristics, temporal dependences, and distributional properties of historical flows. We also show that both including conditional information of climatic teleconnection signals and developing the downscaling in cascades decrease significantly the mean error between synthetic and observed flow traces. The downscaling framework is tested with data from the Payette River Basin in Idaho.Item Open Access Topographic and diurnal influences on storms associated with heavy rainfall in northern Colorado(Colorado State University. Libraries, 2024) Douglas, Zoe A., author; Rasmussen, Kristen L., advisor; Bell, Michael M., committee member; Kampf, Stephanie K., committee memberDespite its profound impacts on agricultural and socioeconomical conditions globally, heavy rainfall is a high-impact weather phenomenon of which we have limited quantitative understanding and forecast skill. The Prediction of Rainfall Extremes Campaign in the Pacific (PRECIP) planned to observe the spectrum of heavy rainfall events in the moisture-rich environment of Taiwan and Japan during 2020, but was delayed until 2022 due to the global COVID-19 pandemic. As a result of this unanticipated delay, the PRECIP science team conducted the Preparatory Rockies Experiment for the Campaign in the Pacific ("PRE"-CIP), which observed precipitation over northern Colorado from May to August 2021 using Colorado State University's ground-based research radars and radiosondes. Extreme precipitation features are identified in the radar data and organized into storm modes based on prior research on the Tropical Rainfall Measuring Mission satellite's Precipitation Radar. An "ingredients-based" approach provides a theoretical framework to separate the storm modes into a spectrum of storm intensity and duration during the entire "PRE"-CIP field project, allowing us to connect storm modes to the topography, diurnal cycle, and overall rainfall characteristics in northern Colorado. While precipitation occurred from the mountains to the plains, the highest concentration of storm tracks calculated from all ground-based radar observations occurred over the Rocky Mountains, regardless of storm duration. The majority of storm tracks are of low intensity and short duration, with over 80% of tracked storms having lifetimes of 1 h or less, suggesting that the general population of warm-season precipitation in northern Colorado is short-lived and of weak intensity. When considering heavy rainfall-producing storms, deep convection is the most dominant storm mode in northern Colorado by up to three orders of magnitude over broader convective and stratiform systems. Deep convection most frequently occurred over the Rocky Mountains in the afternoon, while broader convective and stratiform systems most frequently occurred over the foothills and plains in the evening to nighttime hours. Therefore, diurnal forcing and orographic lift play important roles in the morphology of warm-season precipitation in northern Colorado, as has been seen in mountainous regions across the world. The frequent occurrence of deep convective storms directly over the Rocky Mountains, however, differs from the deep convective hotspots seen in the lowlands downstream of similarly large mountain barriers like the Andes and Himalayas. Ultimately, these radar-based analyses are important for the eventual comparison of heavy rainfall in a semi-arid midlatitude region (Colorado) and a moisture-rich tropical environment (Taiwan and Japan), thus providing an enhanced global understanding of the commonalities of heavy rainfall processes.Item Open Access TREX-SMA: a multi-event hybrid hydrologic model applied at California Gulch, Colorado(Colorado State University. Libraries, 2012) Halgren, James, author; Julien, Pierre Y., advisor; Kampf, Stephanie K., committee member; Gates, Timothy K., committee member; Venayagamoorthy, S. Karan, committee memberThis dissertation describes a hydrologic model, Two-Dimensional Runoff Erosion and Export (TREX) Soil Moisture Accounting (SMA), created from adding the Sacramento Soil Moisture Accounting model (SAC-SMA) to the TREX surface hydrology model. TREX-SMA combines the capabilities of TREX as a distributed physical surface hydrology model with a conceptual rendering of infiltration and return flow as found in SAC-SMA. In order to form the hybrid, infiltrated water (computed as a distributed function on the surface) is aggregated as an input to a system of soil moisture accounting zones, underlying the entire watershed. In each model time step, TREX SMA releases baseflow from the accumulated infiltrated water according to simple transfer functions. Evapotranspiration (ET) losses from the soil moisture zones are computed based on potential ET demand and available water. As baseflow and ET are released between precipitation events, TREX SMA recovers capacity in the soil moisture zones. Based on the simulated recovery, the model then re-initializes the infiltration parameters of the surface model to prepare for the next event, allowing continuous simulation of multiple events. The capabilities of the TREX SMA model to continuously simulate soil moisture, infiltration, and rainfall-runoff are demonstrated with an application to multi-event modeling on the 30 km2 California Gulch watershed, near Leadville, Colorado, United States. Precipitation inputs are derived from measurements at a system of six precipitation and stream flow gauges providing ten-minute data for the summer of 2006. Eight major events were recorded during this time with runoff produced at all gauges. One additional event with partial watershed response was also evaluated for a total of 54 event hydrographs in the 50-day simulated series. Time steps in the simulation ranged between 2.0 and 4.0 seconds. Parameters for the surface hydrology were obtained from a prior calibration of TREX and were distributed across 34,000 grid cells based on the 30-meter United States Geological Survey (USGS) Digital Elevation Model (DEM). Parameters for the soil moisture zones were obtained from a-priori estimates used by the Arkansas Basin River Forecast Center of the National Weather Service (NWS) of the National Oceanographic and Atmospheric Administration (NOAA) in their real-time operational flood forecasting model for the Arkansas River. Using conceptual soil moisture states to re-initialize distributed infiltration parameters, the simulation results with TREX SMA improved relative to results from the unmodified TREX model with constant infiltration parameters. Model results are processed using gnuplot to create real-time hydrograph plots as the simulation progresses. Gnu R scripts produce real-time plots of simulated minus observed residual and statistical analyses as the simulation progresses. Statistics generated for each gauge include Nash-Sutcliffe, percent bias, absolute percent bias, Pearson correlation and modified Pearson correlation, and mean-squared error. These statistics were generated both for the entire simulation series and for each individual storm event. The gnuplot and R plots are produced using web-based technology for instantaneous sharing via the Internet. Model results such as surface and channel water depth are processed with GRASS GIS and KML scripts to create 2.5 dimensional, browseable animations overlaid on a Google Earth terrain. Statistical measures of the improvement of TREX SMA over TREX are presented in this dissertation. The overall accuracy, measured by the Nash-Sutcliffe coefficient, improved in four out of six gauges. Peak over-estimation was corrected in a majority of the 54 peaks evaluated. Implementation of the TREX SMA soil moisture accounting algorithm to re-initialize the infiltration parameters reduces the total absolute peak error from 180% to 135% of the observed peak flow rates. The Nash-Sutcliffe model efficiency improved over standard TREX simulations by 43%, 11%, 5%, and 10% at CG-1, CG-4, CG-6, and SHG09A.Item Open Access Wood in neotropical headwater streams, Costa Rica(Colorado State University. Libraries, 2010) Cadol, Daniel D., author; Wohl, Ellen E., 1962-, advisor; Cenderelli, Daniel A., committee member; Rathburn, Sara L., 1962-, committee member; Kampf, Stephanie K., committee memberWood has been shown to be an integral component of forest streams throughout the temperate climate zone, both in terms of the physical structure of the channel and in terms of aquatic ecosystem function, but the function of wood in undisturbed tropical streams has not been studied. This dissertation represents the first systematic analysis of instream wood in a tropical setting to be published. This study was limited to the headwater streams (drainage area <8.5 km2) of La Selva Biological Station, on the Atlantic margin of Costa Rica, a wet tropical site with limited landslide activity. Although the results are instructive and enable comparisons with the vast temperate instream wood literature, they should not be construed as representative of debris flow-dominated wet tropical forest streams or of dry or seasonal tropical forest streams. Wood loads in the thirty 50-m-long study reaches examined ranged from 3.0 to 34.7 m3 of wood per 100 m of channel length and 41 to 612 m3 of wood per ha of channel area. Average values are 12.3 m3/100 m and 189 m3/ha. These values fall generally in the lower range of wood load reported for temperate streams, with values typically lower than those reported from the Pacific Northwest region and the Great Lakes region and within the range of those reported from the Rocky Mountain region and from Southern Hemisphere study sites. Comparisons to study sites in eastern North America, Europe, and Japan are problematic because La Selva is a generally undisturbed forest, whereas studies from those regions are conducted in streams with significant human impact and tend to have very small wood loads. Flow hydraulics appear to be the dominant control on the lateral distribution of wood in the channels of La Selva, but they are only a partial control on the longitudinal distribution of wood, explaining about half of the variation in wood load among the study sites. The remainder of the variation is likely caused by the stochastic nature of large tree fall. In spite of the high temporal variability of lateral input of wood to the channels, spatial variability is small, partially because of the paucity of landslides at La Selva. Therefore, I propose that instream transport has a greater influence on the longitudinal distribution of wood than lateral input variability. Wood in a representative subset of 10 of the 50-m-long study reaches was monitored for 2.3 years. The wood in the streams of La Selva is more transient than wood in most sites studied in the temperate zone, with piecewise mean residence times ranging from 2 to 12 years and volume-wise mean residence times ranging from 2 to 83 years among the 10 sites monitored. Average values were 5 and 7 years, respectively. These are roughly an order of magnitude shorter than mean residence times reported from the Pacific Northwest, but similar to times reported from the Colorado Rocky Mountains. The short residence times may be a result of more frequent large floods caused by the wet tropical climate, higher decay rates caused by the warm tropical climate, or both. Perhaps because of this transience, wood was found to have minimal influence on flow resistance in a subset of 6 of the 50-m-long study reaches. In contrast, wood has been shown to be a major control on flow resistance in temperate mountain streams. It is possible that the channel geometry and bed material size are adjusted to the frequent high discharges, which also mobilize and rework the wood, causing grain and form resistance to overwhelm any resistance contribution from wood. Instream wood at La Selva also appears to have a minimal influence on sediment transport. Jams in sand-bed channels and jams in boulder-bed channels had no associated residual elevation drop. Jams in gravel-bed channels did alter bed elevation by trapping sediment wedges behind them, but analysis of tracer clast movement at one gravel-bed jam resulted in no observable difference in transport distances or mobility between clasts placed upstream of the jam and those placed downstream. An additional forest-stream interaction that was documented is diel cycles in stream discharge associated with groundwater withdrawal by the forest for evapotranspiration. Analysis of the cycles indicates a strong correlation with vapor pressure differential, which previous researchers have found to correlate with sap flow. Further analysis of the cycles suggests that at low-stage conditions transmissivity dominates groundwater flow into the channel, while at high-stage conditions hydraulic gradient is dominant.