Projecting end-of-century climate extremes and their impacts on the hydrology of a representative California watershed

• Published in: Hydrology and earth system sciences 2022-07, Vol.26 (13), p.3589-3609
• Main Authors: Maina, Fadji Z, Rhoades, Alan, Siirila-Woodburn, Erica R, Dennedy-Frank, Peter-James
• Format: Article
• Language: English
• Subjects: Agricultural production; Agriculture; Aquatic resources; Aquifers; Atmospheric precipitations; California; Climate change; Climate models; Climatic changes; Climatic extremes; Energy balance; ENVIRONMENTAL SCIENCES; Evapotranspiration; Evolution; Fluid mechanics; Geology; Global climate; Groundwater; Hydroclimate; Hydrodynamics; Hydrologic models; Hydrology; Investigations; Moisture effects; Permeability; Physics; Precipitation; Rainfall; River basins; River networks; Rivers; Sediments; Snowmelt; Snowpack; Soil moisture; Storage; Stream flow; Streams; Summer; Surface water; Surface-groundwater relations; Topography; Water resources; Water shortages; Water, Underground; Watershed hydrology; Watersheds; Winter
• ISSN: 1607-7938; 1027-5606; 1607-7938
• DOI: 10.5194/hess-26-3589-2022

In California, it is essential to understand the evolution of water resources in response to a changing climate to sustain its economy and agriculture and to build resilient communities. Although extreme conditions have characterized the historical hydroclimate of California, climate change will likely intensify hydroclimatic extremes by the end of the century (EoC). However, few studies have investigated the impacts of EoC extremes on watershed hydrology. We use cutting-edge global climate and integrated hydrologic models to simulate EoC extremes and their effects on the water-energy balance. We assess the impacts of projected driest, median, and wettest water years under Representative Concentration Pathway (RCP) 8.5 on the hydrodynamics of the Cosumnes River basin. Substantial changes to annual average temperature (>+2.5 ∘C) and precipitation (>+38 %) will characterize the EoC extreme water years compared to their historical counterparts. A shift in the dominant form of precipitation, mostly in the form of rain, is projected to fall earlier. These changes reduce snowpack by more than 90 %, increase peak surface water and groundwater storages up to 75 % and 23 %, respectively, and drive the timing of peak storage to occur earlier in the year. Because EoC temperatures and soil moisture are high, both potential and actual evapotranspiration (ET) increase. The latter, along with the lack of snowmelt in the warm EoC, causes surface water and groundwater storages to significantly decrease in summer, with groundwater showing the highest rates of decrease. These changes result in more ephemeral EoC streams with more focused flow and increased storage in the mainstem of the river network during the summer.