Sterle, K., Hatchett, B., Singletary, L., & Pohll, G. 2019, Hydroclimatic Variability in Snow-fed River Systems: Local Water Managers’ Perspectives on Adapting to the New Normal., Bulletin of the American Meteorological Society, 100: 1031–1048.

Between water years 2012 and 2017, the Truckee–Carson river system in the western United States experienced both historic-low and record-high Sierra Nevada snowpack, anomalously warm temperatures, and winter and spring flooding. As part of an ongoing collaborative modeling research program in the river system, researchers conduct annual interviews with key local water managers to characterize local climate adaptation strategies and implementation barriers, and identify science information needs to prioritize ongoing research activities. This article presents new findings from a third wave of interviews conducted with the same water managers following the historic 2017 wet year. Comparison of these data suggests that managers increased their adaptation efforts described during previous consecutive drought years (2015 and 2016). In 2017, comparatively fewer managers described climate uncertainty as an implementation barrier, exemplifying recent hydroclimate variability as the “new normal” climate for which they should plan. An assessment of recent conditions reveals that recent water years bound historical observations and are consistent with estimated paleoclimate extremes in terms of magnitude, but not persistence, of both dry and wet conditions. Comparison to projected future climate conditions affirms managers’ perspectives that increased hydroclimate variability, inclusive of drought and flood extremes, defines the new normal climate anticipated for the region. To support long-term adaptation planning, managers requested that researchers prioritize simulations of alternative water management strategies that account for nonstationary climate patterns and quantify implications system-wide. This article illustrates how interdisciplinary research that integrates local knowledge with applied climate science research can support adaptive water management in snow-fed river systems.

Snow-fed river system communities are highly sensitive to climate change (IPCC 2014; USGCRP 2017) because the majority of their water supply is derived from snow (Barnett et al. 2005; Mankin et al. 2015; Li et al. 2017). A warmer climate shifts precipitation phase from snow to rain (Knowles et al. 2006), altering snowpack dynamics, shifting peak streamflow timing, reducing groundwater recharge, and increasing winter and spring flooding (Mote et al. 2005; Stewart et al. 2005; McCabe et al. 2007; Jasechko et al. 2014; Trujillo and Molotch 2014; Dettinger et al. 2015; Harpold et al. 2017a). Warmer spring and summer temperatures further compound these “snow droughts” (Harpold et al. 2017b; Hatchett and McEvoy 2018) by increasing evapotranspiration rates and irrigation water demand (Hatchett et al. 2015). This presents critical challenges in managing seasonal water supply and demand engineered for stationary climate patterns (Milly et al. 2008; Georgakakos et al. 2014).

Conducting case study research in snow-fed river systems offers a unique opportunity to examine how hydroclimate variability alters water supply and influences local climate adaptation across diverse and competing water-use communities (McNeeley et al. 2016; Mills-Novoa et al. 2017; Sterle and Singletary 2017; Mostert 2018). Such climate adaptation strategies seek to moderate harm or exploit beneficial opportunities (Adger et al. 2005) in response to climatic stimuli, such as extreme droughts and floods, interannual variability, or changes in long-term average conditions (Smit et al. 2000). Strategies pursued are not exclusive to any one river system (Bierbaum et al. 2013) and ultimately relate to a system’s hydrologic, socioeconomic, and ecological components, and its respective capacities to adapt (Adger et al. 2007; Moser and Boykoff 2013).

Implementation barriers that constrain or impede adaptation, however, may be site-specific (Moser and Ekstrom 2010; Eisenack et al. 2014). In the western United States, for example, enhancing and diversifying water supply to meet growing water demand may be limited by inherent water scarcity and over-allocated water rights (Fuller and Harhay 2010; Padowski and Jawitz 2012; Owen 2014). Adaptation may be further constrained by lack of coordination (Burnham et al. 2016), stemming from longstanding conflict among diverse and competing water-use communities (Barnett et al. 2014; Coleman et al. 2016). In the context of climate change, adapting to snow droughts and atmospheric river (AR)-based flooding (e.g., Ralph et al. 2004, 2006; Konrad and Dettinger 2017) may be constrained by existing prior appropriation based water law and related institutional arrangements (Kates et al. 2012; Gallaher et al. 2013; Pulwarty and Maia 2015; McNeeley 2017). Revising such practices may be further constrained by climate uncertainty (Kates et al. 2012; Bierbaum et al. 2013) associated with human and natural system response to climate change (Liu et al. 2007; Van Loon et al. 2016), or the inability to downscale climate projections to scales useful for adaptation planning (Maurer and Hidalgo 2008; Vicuna et al. 2010; Maurer et al. 2014). Thus, adaptation to climate change is not one single strategy, but rather a set of diverse, intersecting strategies that consider both climate and nonclimatic stressors, such as population growth, ecological change, and evolving water management institutions (Thornton and Manasfi 2010).

A participatory research approach becomes useful in this context to characterize local climate adaptation and implementation barriers and to identify local science information needs (Morss et al. 2005; Engle 2012; McNeeley 2014; Pulwarty and Maia 2015; Burnham et al. 2016; Nava et al. 2016). Collaborative modeling that relies on the systematic and iterative interaction between researchers and key local stakeholders has the potential to harness local knowledge and perspectives useful to prioritize research activities (Langsdale et al. 2013; Beall King and Thornton 2016; Singletary and Sterle 2017, 2018). These interactions seek to clarify stakeholders’ mental models (Beall King and Thornton 2016), generate new knowledge of river system function under climate change (Moser and Ekstrom 2010; Cloutier et al. 2015; Prato 2015; Meadow et al. 2015), and advance applied climate and socio-hydrology research (Sivapalan et al. 2014; Klenk et al. 2015; Fazey et al. 2018; Mostert 2018).

Inspired by this growing body of climate adaptation research, this article reports new findings part of a 5-yr (July 2014–June 2019) collaborative modeling research program underway in the Truckee–Carson river system in California and Nevada of the western United States (Singletary and Sterle 2017, 2018). The program convenes an interdisciplinary research team of hydrologists, climatologists, and resources economists with key local water managers who represent the diverse and competing water-use communities in the river system. Annual interviews are conducted with the same local water managers to 1) assess shifts in climate adaptation strategies and implementation barriers over time (Sterle and Singletary 2017) and 2) identify and prioritize research activities presented at biannual Stakeholder Affiliate Group workshops. Research activities include developing climate scenarios (Dettinger et al. 2017) and simulating locally identified adaptation strategies using hydrologic and operations models tailored to the river system1 (Morway et al. 2016; Sterle et al. 2017).

Building on an already published comparative analysis of interview data collected during the 2015 and 2016 consecutive drought years (e.g., Sterle and Singletary 2017), we append and compare new data collected from a third wave of interviews following the 2017 historic wet year. We enhance this analysis by including an assessment of recent (2012–17) hydroclimate variability in a historical (last 120 years) and paleoclimate (greater than 120 years) context. In this article, we examine the following research questions: 1) How does recent hydroclimate variability compare to historical and paleoclimate climate records? 2) How do water management challenges faced during wet years compare to challenges faced during consecutive drought years? 3) How do local climate adaptation strategies and implementation barriers shift over time in the context of hydroclimate variability? 4) What science information is most useful to support long-term climate adaptation at the river system scale?

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