Adapting to Variable Water Supply in the Truckee-Carson River System, Western USA

Abstract

Abstract:In snow-fed inland river systems in the western United States, water supply depends upon timing, form, and amount of precipitation. In recent years, this region has experienced unprecedented drought conditions due to decreased snowpack, exacerbated by exceptionally warmer winter temperatures averaging 3-4 • C above normal. In the snow-fed Truckee-Carson River System, two sets of interviews were conducted as part of a larger collaborative modeling case study with local water managers to examine local adaptation to current drought conditions. A comparative analysis of these primary qualitative data, collected during the fourth and fifth consecutive years of continued warmer drought conditions, identifies shifts in adaptation strategies and emergent adaptation barriers. That is, under continuous exposure to climate stressors, managers shifted their adaptation focus from short-term efforts to manage water demand toward long-term efforts to enhance water supply. Managers described the need to: improve forecasts and scientific assessments of snowmelt timing, groundwater levels, and soil moisture content; increase flexibility of prior appropriation water allocation rules based on historical snowpack and streamflow timing; and foster collaboration and communication among water managers across the river system. While water scarcity and insufficient water delivery infrastructure remain significant impediments in this arid region, climate uncertainty emerged as a barrier surrounding adaptation to variable water supply. Existing prior appropriation based water institutions were also described as an adaptation barrier, meriting objective evaluation to assess how to best modify these historical institutions to support dynamic adaptation to climate-induced water supply variability. This study contributes to a growing body of research that assesses drought adaptation in snow-fed inland river systems, and contributes a unique report concerning how adaptation strategies and barriers encountered by local water managers change over time under continuous exposure to climate stressors. These locally identified adaptation strategies forward a larger collaborative modeling case study by informing alternative water management scenarios simulated through a suite of hydrologic and operations models tailored to this river system.

Winter Snow Level Rise in the Northern Sierra Nevada from 2008 to 2017

“…These conclusions are despite uncertainties that are posed by storm-scale variability [22], potential bias in snow-fraction calculations because of precipitation gauge collection efficiency [52,53], and errors in snow-level observations. The ability to estimate changes in precipitation phase operates under the assumption that the empirical relationship to calculate snow fraction [15] remains stationary in time and is not sensitive to rain and snow transitions or spatiotemporal variability [46]. Further improvement in the snow-fraction calculations could be obtained by developing site-specific parameter values [46] and using additional observations [5].…”

“…We have provided evidence that the snow-level radar and snow-fraction estimates appear to offer reasonable metrics to observe and evaluate precipitation phase change in snow-dominated watersheds [1,5,[28][29][30]. These changes will have marked effects on warm season streamflow [4], especially during drought years [13]-with negative implications for urban, ecological, and agricultural water demands [13][14][15]64]. If such a connection between SSTs, moisture plume strength, and snow fractions does exist, it suggests that snow accumulation may further decline with continued regional warming.…”

“…Conversely, WY2017 was the wettest year in the past century and followed a near-average WY2016. These wide-ranging hydroclimatic conditions provide incentive to study the physical mechanisms that may be influencing hydrologic variability in the Sierra Nevada, as this knowledge can be used to inform and prioritize adaptation strategies for sustainable water management under a changing climate [15].…”

“…All of these basins are managed for multiple purposes, including flood control, and to meet ecological and human consumptive demands. The relatively low elevation of these basins makes them susceptible to changes in precipitation phase due to warming [18], which has significant implications for winter flooding [9,19] and warm season water availability [15]. Because of the importance of the northern Sierra Nevada for water resources and flood prevention in California and Nevada, a novel network of hydrometeorological measurements exist upstream of the Sierra Nevada [20] and offer a unique means to explore hydroclimatic change in this region.…”

Water management, hydrological extremes, and society: modeling interactions and phenomena

“…Different management strategies have been adopted to reduce the negative impacts of hydrological extremes , Thieken et al 2016, Sterle and Singletary 2017, Sterle et al 2019. Structural measures that address the problem in the short term often generate unintended consequences in the long term because of the feedback mechanisms operating in coupled human-water systems (Garcia et al 2019).…”