Projected Changes to Extreme Runoff and Precipitation Events From a Downscaled Simulation Over the Western United States

Abstract

Extreme precipitation and runoff events, which often impact natural and social systems more than mean changes, generally occur over regional scales. Future climate projections can be used to estimate how the hydrologic cycle may change, but the coarse resolution of global climate models (GCMs) (>1 •) makes it difficult to evaluate regional changes, such as over a single watershed. To estimate changes in hydroclimatic variables at finer spatial resolutions, we dynamically downscale the Community Climate System Model version 4 (CCSM4) with the Weather Research and Forecasting (WRF) regional climate model over the western United States at 9 km spatial resolution. By running WRF at a higher spatial resolution, we estimate future climate conditions, including 99% event magnitude, over 17 watersheds: the Columbia, Lower Colorado, Upper Colorado, the Upper Missouri/Yellowstone, and 12 basins draining the western slope of the Sierra Nevada in California. Over each basin, we compare a historical period (1996-2005) with mid-century (2041-2050) and end-century (2091-2100). From the WRF/CCSM simulations, most basins are projected to have earlier peaks in springtime streamflow. The Columbia and the Lower Colorado watersheds are both expected to experience more extreme wet days, with the 99th percentile of daily precipitation estimated to increase by over 10%. For the Upper Colorado, however, the 99th percentile of daily runoff is projected to decrease by over 30%. Basins in the northern and central Sierra Nevada are projected to have substantial increases in extreme runoff, with doubling of high flow event magnitude possible for some basins. By end-century, the contribution of high-magnitude runoff (>90th percentile) to total runoff is projected to increase from 46 to 56%, when averaged across all 12 Sierra Nevada basins. Though only one realization from a single GCM, the downscaled simulation presented here shows interesting results regarding how extreme events may change; these results can be tested by downscaling other global models with WRF to create an ensemble of dynamically downscaled future projections.

Climate-informed hydrologic modeling and policy typology to guide managed aquifer recharge

“…Our future projections of WAFR provide clear evidence that increases in high-magnitude-flows are highly likely under climate change in California ( Fig. 1 ), as supported by previous studies reporting substantial and robust increases in projected extreme precipitation ( 23 , 31 ) and streamflow ( 16 , 19 , 20 ). Earlier snowmelt and larger increases in rain-on-snow events also contribute to more extreme streamflow ( 32 ), implying higher WAFR under climate change.…”

“…The largest robust increases are concentrated over WAFR-abundant Northern California, including the Sacramento River and North Coast hydrologic regions. These findings are in line with previous research (19,20), which also found substantial and widespread increases in highmagnitude-flow events, especially for basins in the northern and central Sierra Nevada. In contrast, there is almost no increase (and in some cases, even a decrease) in the WAFR-limited dry Southern California (Fig.…”

Bias Correction of Hydrologic Projections Strongly Impacts Inferred Climate Vulnerabilities in Institutionally Complex Water Systems

“…In this study, we explored how our management of the well-known errors and biases in coupled land-atmosphere modeling systems (e.g., WRF-Noah-MP) used to simulate current hydrology (as in this study) and increasingly to project regional climate change impacts (Huang et al 2018;Musselman et al 2018;Schwartz et al 2017;Wrzesien and Pavelsky 2020) can strongly distort our perceptions of vulnerabilities in institutionally complex major global water resources systems such as the north-central California case analyzed in this study. We show how streamflow errors from an atmospheric and land-surface hydrologic model, WRF-Noah-MP, propagate into a water management model, CALFEWS, and affect perceptions of systemwide water supplies, groundwater banking, and the annual revenue of irrigation districts.…”

Transportation Network Companies: Drivers’ Perceptions of Ride-Sharing Regarding Climate Change and Extreme Weather

“…Future climate change studies predict not only warming temperatures in many geographic areas, but also an increasing number of extreme events [36]. Rainfall and snow may be especially susceptible to change towards more extremes in the Sierra Nevada Mountain range [37][38][39] and, thus, have strong impacts on the business of TNC in the future-affecting the companies, the individual drivers, as well as customers taking rides.…”