Abstract
This study analyzed watershed response to climate change and forest fire impacts in the upper Umatilla River Basin (URB), Oregon, using the precipitation runoff modeling system. Ten global climate models using Coupled Intercomparison Project Phase 5 experiments with Representative Concentration Pathways (RCP) 4.5 and 8.5 were used to simulate the effects of climate and fire-burns on runoff behavior throughout the 21st century. We observed the center timing (CT) of flow, seasonal flows, snow water equivalent (SWE) and basin recharge. In the upper URB, hydrologic regime shifts from a snow-rain-dominated to rain-dominated basin. Ensemble mean CT occurs 27 days earlier in RCP 4.5 and 33 days earlier in RCP 8.5, in comparison to historic conditions (1980s) by the end of the 21st century. After forest cover reduction in the 2080s, CT occurs 35 days earlier in RCP 4.5 and 29 days earlier in RCP 8.5. The difference in mean CT after fire-burns may be due to projected changes in the individual climate model. Winter flow is projected to decline after forest cover reduction in the 2080s by 85% and 72% in RCP 4.5 and RCP 8.5, in comparison to 98% change in ensemble mean winter flows in the 2080s before forest cover reduction. The ratio of ensemble mean snow water equivalent to precipitation substantially decreases by 81% and 91% in the 2050s and 2080s before forest cover reduction and a decrease of 90% in RCP 4.5 and 99% in RCP 8.5 in the 2080s after fire-burns. Mean basin recharge is 10% and 14% lower in the 2080s before fire-burns and after fire-burns, and it decreases by 13% in RCP 4.5 and decreases 22% in RCP 8.5 in the 2080s in comparison to historical conditions. Mixed results for recharge after forest cover reduction suggest that an increase may be due to the size of burned areas, decreased canopy interception and less evaporation occurring at the watershed surface, increasing the potential for infiltration. The effects of fire on the watershed system are strongly indicated by a significant increase in winter seasonal flows and a slight reduction in summer flows. Findings from this study may improve adaptive management of water resources, flood control and the effects of fire on a watershed system.
Highlights
Anthropogenic influences on climate coupled with natural variability in climate have shifted the spatial and temporal distribution of water resources worldwide [1,2]
This paper explores the watershed response to climate change in the upper Umatilla River Basin (URB) where runoff behavior is observed before and after fire-burns in the 21st century
Using Precipitation Runoff Modeling System (PRMS), a runoff model was calibrated for the upper URB, to characterize trends in runoff, snowpack, recharge and other components of the water budget to understand water availability in a changing climate and forest cover reduction
Summary
Anthropogenic influences on climate coupled with natural variability in climate have shifted the spatial and temporal distribution of water resources worldwide [1,2]. Quantifying recharge and streamflow response to climate change is an essential step to developing long-term water resource management plans to increase the understanding of the global energy balance in a hydrologic regime to improve adaptive capacity [3,4]. In the Pacific Northwest, climate change impacts include shifts in the magnitude and timing of runoff [8,9,10,11], reduced proportion of precipitation falling as snow in montane regions [12,13], decreases in snow water equivalent [14,15] and an increase in the frequency and intensity of floods and droughts [11,16,17]. The ratio of snow water equivalent to precipitation and potential recharge were quantified
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