Impacts of Climate Change on Hydrology and Water Resources in the Boise and Spokane River Basins

In the Pacific Northwest, warming climate has resulted in a lengthened growing season, declining snowpack, and earlier timing of spring runoff. This study characterizes the impact of climate change in two basins in Idaho, the Spokane River and the Boise River basins. We simulated the basin-scale hydrology by coupling the downscaled precipitation and temperature outputs from a suite of global climate models and the Soil and Water Assessment Tool (SWAT), between 2010 and 2060 and assess the impacts of climate change on water resources in the region. For the Boise River basin, changes in precipitation ranged from −3.8 to 36%. Changes in temperature were expected to be between 0.02 and 3.9°C. In the Spokane River region, changes in precipitation were expected to be between −6.7 and 17.9%. Changes in temperature appeared between 0.1 and 3.5°C over a period of the next five decades between 2010 and 2060. Without bias-correcting the simulated streamflow, in the Boise River basin, change in peak flows (March through June) was projected to range from −58 to +106 m3/s and, for the Spokane River basin, the range was expected to be from −198 to +88 m3/s. Both the basins exhibited substantial variability in precipitation, evapotranspiration, and recharge estimates, and this knowledge of possible hydrologic impacts at the watershed scale can help the stakeholders with possible options in their decision-making proces

Climate Change Impacts: An Assessment for Water Resources Planning and Management in the Pacific Northwest of the U.S

Assessing the hydrological impacts of climate change in the Pacific Northwest (PNW) region of the United States is important. Many global circulation models (GCMs) have a wide range of temperature and precipitation predictions for the PNW region (Bureau of Reclamation, 2011). Numerous studies have reported that decreasing snow pack, increasing temperatures and decreasing streamflow for many basins. For instance, Mote (2003) indicates that annual average temperatures in the Northwest rose faster than the global average during the 20th century. This warming occurred mostly during the winter and spring. The predominance of winter and spring warming, especially in regard to extreme minimum temperatures, was confirmed more recently in a smaller study at two locations: one in Western Montana and the other in British Columbia (Caprio et al., 2009). The warming climate has resulted in a lengthened growing season (Kunkel et al., 2004), decline of snowpack (Mote, 2006), and earlier timing of the spring runoff (Stewart et al., 2005; Hamlet and Lettenmaier, 1999). Water supply in the West is vulnerable to climatic change, mainly because it relies heavily upon the capture of the spring runoff. Precipitation typically accumulates in the mountains as snowpack and is released during the spring melt, which may continue at high elevations into July. Warmer temperatures are likely to lead to more rain and less snow in the winter, causing an increase in the wintertime streamflow and decrease in spring runoff. Warmer weather is also likely to cause snowpack to retreat to higher elevations and experience earlier melt (Hamlet and Lettenmaier, 1999)

Hydrological Behavior of Grasslands of the Sandhills of Nebraska: Water and Energy Balance Assessment from Measurements, Treatments and Modeling

Understanding energy and water balance processes in the Sandhills is crucial to assess the land-atmosphere feedback effects. The Sandhills located in western Nebraska covers a vast grassland ecosystem with limited variability in vegetation and soil. However, the combined effect of topography, land cover and micrometeorology by subjecting the land surface to various disturbances and treatments is rarely studied. The NOAH Land Surface Model was used to estimate net radiation, latent, sensible and ground heat fluxes as well as water balance components for two growing seasons between 2005 and 2006 in various plots at the Grasslands Destabilization Experimental site where these plots were subjected to four different treatments and located at two topographical locations namely high and low positions. The simulated results of net radiation and ground heat fluxes correlated well with measurements. While the amount of precipitation received was between 900 and 1000 mm for both seasons, on a daily and sub-daily time scale, the partitioning of net radiation into latent, sensible and ground heat fluxes showed high variability across the plots, primarily driven by vegetation and soil moisture. Total evapotranspiration and soil moisture averages suggested the influence of vegetation and timing of precipitation also in controlling various land surface processes in the Sandhills. This study provides a framework for using the LSM to quantify the feedback effects and emphasizes the importance of microtopography and land treatments in the model environment

Relating Climatic Attributes and Water Resources Allocation: A Study Using Surface Water Supply and Soil Moisture Indices in the Snake River Basin, Idaho

Climate change forced by anthropogenic activities has been ongoing since at least the beginning of the industrial revolution. Part of the recent warming in the western United States has been attributed to anthropogenic climate change. This research seeks to answer the basic question of how declining streamflow, increasing temperatures, and fluctuation in precipitation have impacted water resource allocation in the Snake River Plain over the past 35 years (1971-2005). Understanding how changes in climatic attributes have historically impacted water allocation should help water managers better understand how projected climate change may influence allocation. Annual and monthly diversion trends from 62 locations in the Snake River Plain were compared to temperature and precipitation trends at 10 climate stations across the basin. We found a strong trend of declining annual surface water diversions across the study area. Of the 62 diversion points examined, 45 have highly significant decreasing annual diversion trends while an additional 8 have significant decreasing trends. Despite the annual decline in surface water diversions, April diversions have increased at more than half of the diversion points, with 15 locations showing highly significant trends and an additional 17 showing significant increasing diversion trends. A comparison of diversions to the Surface Water Supply Index (SWSI) indicates that the decline in mid and late season diversions is mostly caused by decreasing supply in the study period, while a comparison of diversions to Palmer’s Z-index and the Standardized Precipitation Index (SPI) indicates that early season diversions are highly correlated to early season moisture anomalies

Estimation of the Water Balance Using Observed Soil Water in the Nebraska Sandhills

Analyzing the dynamic hydrologic conditions of the Sandhills is critical for water and range management, sustainability of the Sandhills ecosystem as well as for dune stability. There are complex models available to quantify both surface and subsurface hydrological processes. However, we present in this study an application of a relatively simple model to arrive at best estimates of the water balance components. Using the Thornthwaite-Mather (TM) model, water balance components were estimated for 4 Automated Weather Data Network (AWDN) weather monitoring stations. Estimated averages of the water balance components suggested that mean annual precipitation of these four sites was only about 420 mm but water loss through plant evapotranspiration (ET) was 861 mm, with PET of about 1214 mm. Our investigation shows that there was surplus of water between December and March and a deficit occurs at the start of the growing season in May and extends through senescence in September-October. This study also suggests that the High Plains aquifer possibly met the plant water requirement during this deficit period as well as during the soil water extraction period, from May through September

Closure to Estimation of the Water Balance Using Observed Soil Water in the Nebraska Sandhills

We are thankful to Szilagyi [2010] for providing us an opportunity to discuss the important points of our paper [Sridhar and Hubbard, 2010]. We demonstrated a seasonal water balance assessment using the Modified Thornthwaite-Mather (TM) model in the Nebraska Sandhills. We computed the water budget for a few representative weather monitoring stations located in the Sandhills using the high resolution soil moisture data to assess the storage. In our water balance analysis, soil moisture storage is determined based on observed soil moisture and actual evapotranspiration, ETact was computed for each month using the change in storage in soil water and precipitation. If the change in storage is positive based on our observed soil moisture, we considered two scenarios and the least of the two is considered for computing actual ET

Effects of Coupling in Understanding the Surface Energy Balance in the Snake River Basin, Idaho

An accurate estimation of surface fluxes and evapotranspiration is critical in understanding the hydrological and meteorological processes linking the land and the atmosphere. Due to difficulties in obtaining extensive and timely field measurements, land surface and atmospheric models are widely employed in estimating such fluxes. This study focuses on testing the ability of Noah LSM to simulate the surface fluxes both in an uncoupled mode and coupled within an atmospheric model. An agricultural area in the Snake River Basin in Idaho and its surrounding natural vegetation regions are the study area. Two model improvements are tested in this investigation: modification to the calculations of the surface exchange coefficient and the addition of an irrigation scheme to increase available water to crop areas. Results show that these changes are significant factors in proper modeling of hydrological and atmospheric process, but improvements and additional calibration to different regions are still needed

The Adaptability and Sustainability of Surface Water Diversions Along the Main Stem of the Snake River in Southern Idaho

Agriculture in southern Idaho depends heavily on the conversion of snowpack into spring runoff. The Natural Resource Conservation Service (NRCS) has developed a Surface Water Supply Index (SWSI) as a tool to predict whether or not forecasted runoff and reservoir storage will be adequate to meet irrigator’s needs at a basin scale. This research by comparing SWSI to diversions for individual canals advances the use of SWSI to develop a Surface Water Supply Metric (SWSM) that can be used to estimate the reliability and sustainability of diversions under historic and projected time periods. An historic analysis of diversions during three time periods 1928-1957, 1960-1980, and 1980-2009 indicates how the construction of Palisades Reservoir in 1956 allowed some canals to increase diversions, while other canals where able to improve the reliability of diversions. The analysis also highlights how decreasing diversions by irrigators (10% and 13% in July and August, respectively) from the Twin Falls North Side Canal Compnay has increased diversion reliability in those months. The second section of the research uses the SWSM to assess the sustainably of diversions under three projected climate change scenarios. All projected flow scenarios were run using a system dynamics version of the Snake River Planning Model (SRPM) developed by the authors. SRPM is currently used by the Idaho Department of Water Resources (IDWR) to plan water resource management in the Snake River basin. The analysis indicates based on the projected climate scenarios analyzed that upstream irrigators may see a significant decline in reliability while downstream users may see improved irrigation reliability

Explaining the Hydroclimatic Variability and Change in the Salmon River Basin

Climate change in the Pacific Northwest and in particular, the Salmon River Basin (SRB), is expected to bring about 3–5 °C rise in temperatures and an 8 % increase in precipitation. In order to assess the impacts due to these changes at the basin scale, this study employed an improved version of Variable Infiltration Capacity (VIC) model, which includes a parallel version of VIC combined with a comprehensive parameter estimation technique, Shuffled Complex Evolution (SCE) to estimate the streamflow and other water balance components. Our calibration (1955–1975) and validation (1976–1999) of the model at the outlet of the basin, White Bird, resulted in an r2 value of 0.94 which was considered satisfactory. Subsequent center of timing analysis showed that a gradual advancement of snowmelt induced-peak flow advancing by about 10 days in the future. Historically, the flows have shown a general decline in the basin, and in the future while the magnitudes might not be greatly affected, decreasing runoff of about 3 % over the next 90 years could be expected and timing of peak flow would shift by approximately 10 days. Also, a significant reduction of snow water equivalent up to 25 %, increased evapotranspiration up to 14 %, and decreased soil moisture storages of about 2 % is predicted by the model. A steady decline in SWE/P from the majority of climate model projections for the basin was also evident. Thus, the earlier snowmelt, decreasing soil moisture and increased evapotranspiration collectively implied the potential to trigger drought in the basin and could affect the quality of aquatic habitats and their spawning and a detailed investigation on these impacts is warranted