Grantee Research Project Results
Final Report: Assessing the Impact of a Warmer Climate on Stream Water Quality Across theMountainous Western United States.
EPA Grant Number: R834191Title: Assessing the Impact of a Warmer Climate on Stream Water Quality Across theMountainous Western United States.
Investigators: Stewart-Frey, Iris , Maurer, Edwin
Institution: Santa Clara University
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 2009 through August 31, 2012 (Extended to August 31, 2013)
Project Amount: $250,000
RFA: Consequences of Global Change for Water Quality (2008) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Climate Change , Watersheds , Aquatic Ecosystems , Water
Objective:
Stream temperature, dissolved oxygen (DO), and sediment concentrations play a crucial role in the life cycle and habitat distribution of aquatic species, determine the suitability of water resources for human use, and are expected to be affected by projected climatic changes. Projections of future stream water quality parameters are particularly important for regions such as the mountainous western U.S., where water resources are already limited, air temperatures are projected to warm significantly, and runs of important cold water species, such as salmon and trout, are threatened. The objective of this work, then, is to project changes in water flow and water quality for the mountainous areas of the western U.S. through the end of the century using an ensemble of downscaled GCM output (16 models) and two emission scenarios, to drive an established watershed model (SWAT) with an improved stream temperature model. The output is analyzed to further the understanding of changes in hydrologic flows components (precipitation, evapotranspiration, snowmelt, streamflow, surface flow, subsurface flow, soil and groundwater storage) and water quality across GCM models, emission scenarios, geological and elevational differences, and on different temporal and spatial scales. The understanding gained from this project and the sub-basin modeling scale aid in identifying the critical areas in watersheds for best management practices with the goal of maintaining or improving water quality for both human consumption and fish and wildlife habitat.
Summary/Accomplishments (Outputs/Outcomes):
A new stream temperature model provides enhanced empirical simulation of stream temperature, by accounting for local heat contributions, heat transfer with water routing, and heat exchange when flowing through the stream. In comparison to other approaches, the model from our study is not dependent on any site-specific empirical relationships between air and stream and (in contrast to full heat-budget approaches) does not require more parameter information beyond what is already provided by the user. The new model outperforms the standard SWAT stream temperature model, especially for mountain streams where warmer air temperatures result in increased snowmelt and cooler stream temperatures.
Based on a 16-model ensemble of downscaled GCM output, temperatures in the sub-basins of the mountainous Western US are expected to increase, with the largest increases in the inland portions of the Columbia River Basin (CRB) and Upper Colorado Basin (UCRB). Precipitation projections vary spatially, between GCMs and between emission scenarios, with somewhat larger increases in precipitation in the Northern SN and CRB than the southern SN and the UCRB. Our work shows that the effects of warmer temperatures generally dominate over the modest projected precipitation increases or decreases in the region.
SWAT hydrologic simulations for the Sierra Nevada (CA) show that by the end of the century, projected climatic warming and earlier snowmelt will impacts not only streamflow, but also evapotranspiration, surface, and subsurface flows, such that less water is available in spring and summer. By the 2080’s, close to 90% of the subwatersheds are expected to have a snowmelt contribution that is less than half of average historical snowpack. Annual streamflow are likely to be reduced, especially at mid-elevations.
For the UCRB, streamflow changes propagate from headwaters to Lee’s Ferry outflow. Under projected climatic changes, spring streamflow, an important contribution to annual flow, is likely to decrease by 20–90%. Snowmelt is likely to decrease by up to 80% throughout the mid and low elevations of the upper Colorado River Basin. The lower elevation areas where the largest decreases in spring streamflow and snowmelt are expected, are the most likely to stay or become arid landscapes, while the highest elevations are likely to remain mostly humid.
For the highly seasonal, water-limited, and mountainous basins such as exist in the Sierra Nevada (CA), substantial changes in water quality can be expected under future climates. These changes are especially significant for the spring and summer seasons and include a) stream temperature increases by up to 6 ºC for summer, reaching close to 30 ºC in the lower elevation reaches, b) decreases of DO by 2–12%, and c) overall decreases in sediment concentrations. These projected water quality changes can impact both human and ecosystem health.
Next-generation climate projections under the Coupled Model Intercomparison Project Phase 5 (CMIP5) are currently replacing those of Phase 3 (CMIP3). In a follow-up study evaluate whether differences in projected climate under CMIP5 necessitate a reconsideration of the expected hydrologic impacts for the mountainous runoff-generating regions of the WUS (Upper Colorado River (UCRB), Columbia River (CRB), and Sierra Nevada (SN) Basins.) We find warmer and wetter projections for the CMIP5 ensemble compared to the CMIP3 ensemble, especially for the UCRB. Similar annual streamflow volumes are projected under CMIP3 and CMIP5, except for the UCRB, where CMIP5 suggests increases in future streamflows. Under CMIP5, all WUS regions are likely to experience similar shifts in streamflow timing as CMIP3, and yet greater declines in snowmelt runoff. We conclude that CMIP3 and CMIP5 output will produce similar hydrology for the CRB and SN and that the UCRB should be further reevaluated under CMIP5 projections (Ficklin, et al., 2014, submitted to Climatic Change).
Conclusions:
Water quality parameters such as stream temperature, dissolved oxygen (DO), and sediment concentrations play a crucial role in the life cycle and habitat distribution of aquatic species, and determine the suitability of water resources for human use. Warmer water temperatures expected from climatic changes affect the self-purification capacity of rivers by reducing the amount of oxygen that can be dissolved and used for biodegradation.Water quality changes across the mountainous Western North America are of particular concern, as surface air temperatures in this region are expected to increase substantially with expected climatic changes, and this region is already water-limited, with the snowmelt at high elevations serving as a large reservoir for water resources. It has been recognized that stream temperature is a complex function of both climatic and hydrological changes, especially in mountainous regions, and stream temperature response to expected global changes is likely to substantially differ between watersheds. In addition, streams in the region contain some high-profile aquatic species, such as salmon and trout, whose health and habitat distribution are dependent on particular flow patterns and comparatively cool stream temperatures.
Our findings are significant in the field, as they a) simulate water flow and quality at the sub-basin scale for a sub-continental region, facilitating an evaluation of the spatial variation in climatic responses, b) used a newly developed stream temperature mixing model, c) use downscaled climate information from 2 emission scenarios and 16 GCMs, allowing for an evaluation across scenarios and models, and d) assess not only stream temperature but also dissolved oxygen and sediment flow changes. The understanding gained from this project and the sub-basin modeling scale aid in identifying the critical areas in watersheds for best management practices with the goal of maintaining or improving water quality and fish and wildlife habitat. Thus the results of the proposed work will be useful in water management analysis and policy planning, which is in line with the EPA’s mission to protect human health and safeguard the natural environment (air, water, and land), on which life depends. Adequate water supplies of sufficient quality are essential for human consumption, agricultural uses, and healthy water bodies, especially in water-limited, rapidly developing regions such as the Southwest. Furthering our understanding how water flow and quality will likely be affected by expected climatic changes at the local scale helps the EPA and local stakeholders in the development of adaptation and mitigation strategies to protect both human and ecosystem health. The insights gained from the work presented here could aid in prioritizing the management of particular mountain streams in the Sierra Nevada and other arid and semi-arid regions. For example, providing riparian shading may mitigate some of the effects of global change on stream temperature.
In addition, results from the western U.S. could give an indication of how other arid mountain systems may be affected by global changes in the future. One important transferable result is that climate-driven changes exhibit a large degree of spatial variability and that the local hydrology needs to be characterized in order to project water quality. Another insight is that the magnitude of the impact of climatic changes is highly dependent on the season. For seasonal, snowmelt-dominated, arid basins, low flow reaches at the mid- and lower elevations without a significant groundwater component are likely to experience not only a shift in the timing of flow with global warming, but also substantially higher stream temperatures during the low flow season, concurrent with a significant decline in water quality and the associated impact on freshwater reserves and native species.
Journal Articles on this Report : 10 Displayed | Download in RIS Format
Other project views: | All 26 publications | 10 publications in selected types | All 10 journal articles |
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Ayers J, Ficklin DL, Stewart IT, Strunk M. Comparison of CMIP3 and CMIP5 projected hydrologic conditions over the Upper Colorado River Basin. International Journal of Climatology 2016;36(11):3807-3818. |
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Ficklin DL, Stewart IT, Maurer EP. Projections of 21st century Sierra Nevada local hydrologic flow components using an ensemble of General Circulation Models. Journal of the American Water Resources Association 2012;48(6):1104-1125. |
R834191 (2011) R834191 (2012) R834191 (Final) |
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Ficklin DL, Luo Y, Stewart IT, Maurer EP. Development and application of a hydroclimatological stream temperature model within the Soil and Water Assessment Tool. Water Resources Research 2012;48:W01511. |
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Ficklin DL, Stewart IT, Maurer EP. Climate change impacts on streamflow and subbasin-scale hydrology in the Upper Colorado River Basin. PLoS One 2013;8(8):e71297. |
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Ficklin DL, Stewart IT, Maurer EP. Effects of projected climate change on the hydrology in the Mono Lake Basin, California. Climatic Change 2013;116(1):111-131. |
R834191 (2011) R834191 (2012) R834191 (Final) |
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Ficklin DL, Stewart IT, Maurer EP. Effects of climate change on stream temperature, dissolved oxygen, and sediment concentration in the Sierra Nevada in California. Water Resources Research 2013;49(5):2765-2782. |
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Ficklin DL, Barnhart BL, Knouft JH, Stewart IT, Maurer EP, Letsinger SL, Whittaker GW. Climate change and stream temperature projections in the Columbia River basin: habitat implications of spatial variation in hydrologic drivers. Hydrology and Earth System Sciences 2014;18(12):4897-4912. |
R834191 (Final) R834195 (Final) |
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Ficklin DL, Letsinger SL, Stewart IT, Maurer EP. Assessing differences in snowmelt-dependent hydrologic projections using CMIP3 and CMIP5 climate forcing data for the western United States. Hydrology Research 2016;47(2):483-500. |
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Stewart IT, Ficklin DL, Carrillo CA, McIntosh R. 21st century increases in the likelihood of extreme hydrologic conditions for the mountainous basins of the Southwestern United States. Journal of Hydrology 2015;529(Part 1):340-353. |
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Willmott CJ, Robeson SM, Matsuura K, Ficklin DL. Assessment of three dimensionless measures of model performance. Environmental Modelling & Software 2015;73:167-174. |
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Supplemental Keywords:
climate change, streamflow, streamflow timing, stream temperature, water quality, western U.S., hydrology, SWAT, stream temperature model, RFA, Air, climate change, Air Pollution Effects, Atmosphere, environmental monitoring, water resources, climate modelsRelevant Websites:
Iris Stewart-FreyProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.