Abstract

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 build resilient communities. Although extreme conditions have characterized the historical hydroclimate of California, climate change will likely intensify hydroclimatic extremes by the End of 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 a Representative Concentration Pathway (RCP) 8.5 on the hydrodynamics of the Cosumnes river basin. High temperatures (> 2.5 °C) and precipitation (> 38 %) will characterize the EoC extreme water years compared to their historical counterparts. Also, precipitation, mostly in the form of rain, is projected to fall earlier. This change reduces snowpack by more than 90 %, increases peak surface water and groundwater storages up to 75 % and 23 %, respectively, and makes these peak storages 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, cause surface water and groundwater storages to significantly decrease in summer, with groundwater showing the highest rates of decrease. Besides, the changes in the precipitation phase lead the lower-order streams to dry out in EoC summer whereas the mainstream experiences an increase in storage.

Highlights

  • California, the fifth largest economy in the world, hosts one of the largest agricultural regions in the United States and is home to over 39 million people

  • Our study focused on End of Century (EoC) projections, we found that compared to the historical median water year (WY), annual surface water will increase by 19% in the EoC median WY

  • Mallakpour et al, (2018) had a similar finding in a study that shows that future California streamflow is altered to Maurer & Duffy, (2005) under both the RCP4.5 and RCP8.5 emissions scenarios, with RCP8.5 showing the highest changes during peak flow

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Summary

Introduction

California, the fifth largest economy in the world, hosts one of the largest agricultural regions in the United States and is home to over 39 million people. Understanding how water resources will evolve under a changing climate is crucial for sustaining the state’s economy and agricultural productivity. The region is especially susceptible to climate change given its reliance on the Sierra Nevada Mountain snowpack as a source of water supply (e.g., Dettinger & Anderson, 2015). Given that precipitation falls predominantly in winter months and the summers are hot and dry, the snow accumulated during the winter provides important water storage for the dry season and is crucial to meet urban demand, sustain ecosystem function, and maintain agricultural productivity (Bales et al, 2006; Dierauer et al, 2018). Any significant reduction in the snowpack will drastically affect the hydrology of the state (Barnett et al, 2005; Harpold & Molotch, 2015; Milly et al, 2005; Rhoades et al, 2018 a,b)

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