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Considerable interest lies in understanding the hydrologic response to climate change in the upper Deschutes Basin, particularly as it relates to groundwater fed streams. Much of the precipitation occurring in the recharge zone falls as snow. Consequently, the timing of runoff and recharge depend on accumulation and melting of the snowpack. Numerical modeling can provide insights into evolving hydrologic system response for resource management consideration. A daily mass and energy balance model known as the Deep Percolation Model (DPM) was developed for the basin in the 1990s. This model uses spatially distributed data and is driven with daily climate data to calculate both daily and monthly mass and energy balance for the major components of the hydrologic budget across the basin. Previously historical daily climate data from weather stations in the basin was used to drive the model. Now we use the University of Washington Climate Impact Group's 1/16th degree daily downscaled climate data to drive the DPM for forecasting until the end of the 21st century. The downscaled climate data is comprised from the mean of eight GCM simulations well suited to the Pacific Northwest. Furthermore, there are low emission and high emission scenarios associated with each ensemble member leading to two distinct means. For the entire basin progressing into the 21st century, output from the DPM using both emission scenarios as a forcing show changes in the timing of runoff and recharge as well as significant reductions in snowpack. Although the DPM calculated amounts of recharge and runoff varies between the emission scenario of the ensemble under consideration, all model output shows loss of the spring snowmelt runoff / recharge peak as time progresses. The response of the groundwater system to changing in the time and amount of recharge varies spatially. Short flow paths in the upper part of the basin are potentially more sensitive to the change in seasonality. However, geologic controls on the system cause this signal to attenuate as it propagates into the lower portions of the basin. This scale-dependent variation to the response of the groundwater system to changes in seasonality and magnitude of recharge is explored by applying DPM calculated recharge to an existing regional groundwater flow model.
The North American Monsoon (NAM) is characterized by high inter- and intra-seasonal variability, and potential climate change effects have been forecasted to increase this variability. The potential effects of climate change to the hydrology of the southwestern U.S. is of interest as they could have consequences to water resources, floods, and land management. I applied a distributed watershed model, the Triangulated Irregular Network (TIN)-based Real-time Integrated Basin Simulator (tRIBS), to the Beaver Creek basin in Arizona. This sub-basin of the Verde River is representative of the regional topography, land cover, and soils distribution. As such, it can serve to illustrate the utility of distributed models for change assessment studies. Model calibration was performed utilizing radar-based NEXRAD data, and comparisons were done to two additional sources of precipitation data: ground-based stations and the North American Land Data Assimilation System (NLDAS). Comparisons focus on the spatiotemporal distributions of precipitation and stream discharge. Utilizing the calibrated model, I applied scenarios from the HadCM3 General Circulation Model (GCM) which was dynamically downscaled by the Weather Research and Forecast (WRF) model, to refine the representation of Arizona's regional climate. Two time periods were examined, a historical 1990-2000 and a future 2031-2040, to evaluate the hydrologic consequence in the form of differences and similarities between the decadal averages for temperature, precipitation, stream discharge and evapotranspiration. Results indicate an increase in mean air temperature over the basin by 1.2 C. The average decadal precipitation amounts increased between the two time periods by 2.4 times that of the historical period and had an increase in variability that was 3 times the historical period. For the future period, modeled streamflow discharge in the summer increased by a factor of 3. There was no significant change in the average evapotranspiration (ET). Overall trends of increase precipitation and variability for future climate scenarios have a more significant effect on the hydrologic response than temperature increases in the system during NAM in this study basin. The results from this study suggest that water management in the Beaver Creek will need to adapt to higher summer streamflow amounts.
Groundwater-level monitoring in the upper Deschutes Basin of central Oregon from 1997 to 2008 shows water-level declines in some places that are larger than might be expected from climate variations alone, raising questions regarding the influence of groundwater pumping, canal lining (which decreases recharge), and other human influences. Between the mid-1990s and mid-2000s, water levels in the central part of the basin near Redmond steadily declined as much as 14 feet. Water levels in the Cascade Range, in contrast, rose more than 20 feet from the mid-1990s to about 2000, and then declined into the mid-2000s, with little or no net change.
"Seasonally snow-dominated, mountainous watersheds supply water to many human populations globally. However, the timing and magnitude of water delivery from these watersheds has already and will continue to change as climate is altered. Associated changes in watershed vegetation cover further affect the runoff responses of watersheds, from altering evapotranspiration rates to changing surface energy fluxes, and there exists a need to incorporate land cover change in hydrologic modeling studies. However, few land cover projections exist at the scale needed for watershed studies, and current models may be unable to simulate key interactions that occur between land cover and hydrologic processes. To help address this gap in the literature, we explored the impacts of climate and land cover change on hydrologic regimes in the Upper Boise River Basin, Idaho. Using a multiagent simulation framework, Envision, we built a hydrologic model, calibrated it to historic streamflow and snowpack observations, and ran it to year 2100 under six diverse climate scenarios. Under present land cover conditions, average annual discharge increased by midcentury (2040-2069) with 13% more runoff than historical (1950-2009) across all climate scenarios, with ranges from 6-24% of increase. Runoff timing was altered, with center of timing of streamflow occurring 4-17 days earlier by midcentury. Our modeled snowpack was more sensitive to warming at lower elevations, and maximum snow water equivalent decreased and occurred 13-44 days earlier by midcentury. Utilizing metrics applicable to local water managers, we see the date that junior water rights holders begin to be curtailed up to 14 days earlier across all models by the end of the century, with one model showing this could occur over a month earlier. These results suggest that current methods of water rights accounting and management may need to be revised moving into the future. To test the sensitivity of our hydrologic model to changes in land cover, we selected a projected future land cover from the FORE-SCE (FOREcasting SCEnarios of land-use change) model. Our future land cover produced less evapotranspiration and more runoff, which stemmed from misclassification of high elevation regions between the FORE-SCE model and our initial land cover dataset, due to changes in the NLCD (National Land Cover Database) classification methodology. Additionally, FORE-SCE does not explicitly model wildfire or vegetative response to climate, both of which will likely be major drivers of landscape change in the mountainous, forested, western U.S., potentially making it insufficient for land cover projections in these areas. With evapotranspiration being the only parameter changing between land cover types in our hydrologic model, we were unable to capture the totality of hydrologic response to land cover change and other models may be better suited for such studies. This study highlights the necessity for better land cover projections in natural ecosystems that are attuned to both natural (e.g., climate, disturbance) and anthropogenic (e.g. management, invasive species) drivers of change, as well as better feedback in hydrologic models between the land surface and hydrological processes."--Boise State University ScholarWorks.
The Pacific Northwest is dependent on seasonal snowmelt for water resources that support a significant portion of its economy. Increased temperatures resulting from higher concentrations of atmospheric greenhouse gases may cause disruptions to these resources because of reductions in the annual snowpack and variations of the timing of snowmelt. This study reconstructs and applies a GIS-based distributed hydrologic model at a monthly scale to assess the effects of future climate change on runoff from the Upper Clackamas River Basin (located near Portland, Oregon). Historic flow data and snow measurements are used to calibrate and test the perfonnance of the hydro logic model for a contemporary period (1971-2000), and the model is run for two future scenarios (2010-2039 and 2070-2099) using IS92 climate change scenarios from two global climate circulation models (Hadley and Canadian Centre for Climate) as inputs. The results forecast that mean peak snowpack in the study area will drop dramatically (36% to 49% by 2010-2039, and 83% to 88% by 2070-2099), resulting in earlier runoff and diminished spring and summer flows. Increases to mean winter runoff by by the 2070-2099 period vary from moderate (13.7%) to large (46.4%), depending on the changes to precipitation forecasted by the global climate circulation models. These results are similar to those of other studies in areas dependent on snowpack for seasonal runoff, but the reductions to snowpack are more severe in this study than similar studies for the entire Columbia Basin, presumably because the elevations of much of the Upper Clackamas Basin are near the current mid-winter snow line.
The Tianshan Mountains, known as the "Water tower of Central Asia", are an essential freshwater source for downstream rivers, residents, irrigation agriculture and ecosystems in Central Asia. Climate in this semiarid region has changed from warm-dry to warm-wet in the last decades. Water resources are highly sensitive to climate change, and their availability is expected to become more unstable in the future. However, hydrological processes in glacierized basins are poorly known due to data scarcity and complex snow and glacier melt dynamics. It is therefore particularly important to improve our understanding of climate change and its impacts on hydrological regimes in dry, glacierized mountain regions such as the Tianshan Mountains. Emphasizing the research gaps related to the scarcity of observational data and lack of understanding of climate variability and hydrological regimes, the aim of this thesis is to model hydrological responses to climate change in a data-scarce glacierized basin in the Tianshan Mountains to better understand mountain hydrology. Spatio-temporal changes of climate change, climate extremes, hydrological and cryosphere were summarized based on data analysis and literature review. ...