Western water and climate change

Abstract

The western United States is a region long defined by water challenges. Climate change adds to those historical challenges, but does not, for the most part, introduce entirely new challenges; rather climate change is likely to stress water supplies and resources already in many cases stretched to, or beyond, natural limits. Projections are for continued and, likely, increased warming trends across the region, with a near certainty of continuing changes in seasonality of snowmelt and streamflows, and a strong potential for attendant increases in evaporative demands. Projections of future precipitation are less conclusive, although likely the northern-most West will see precipitation increases while the southernmost West sees declines. However, most of the region lies in a broad area where some climate models project precipitation increases while others project declines, so that only increases in precipitation uncertainties can be projected with any confidence. Changes in annual and seasonal hydrographs are likely to challenge water managers, users, and attempts to protect or restore environmental flows, even where annual volumes change little. Other impacts from climate change (e.g., floods and water-quality changes) are poorly understood and will likely be location dependent. In this context, four iconic river basins offer glimpses into specific challenges that climate change may bring to the West. The Colorado River is a system in which overuse and growing demands are projected to be even more challenging than climate-change-induced flow reductions. The Rio Grande offers the best example of how climate-change-induced flow declines might sink a major system into permanent drought. The Klamath is currently projected to face the more benign precipitation future, but fisheries and irrigation management may face dire straits due to warming air temperatures, rising irrigation demands, and warming waters in a basin already hobbled by tensions between endangered fisheries and agricultural demands. Finally, California's Bay-Delta system is a remarkably localized and severe weakness at the heart of the region's trillion-dollar economy. It is threatened by the full range of potential climate-change impacts expected across the West, along with major vulnerabilities to increased flooding and rising sea levels.

Weather, habitat composition, and female behavior interact to modify offspring survival in Greater Sage‐Grouse

“…Climate models predict that southwestern North America will experience more frequent and severe droughts (Dettinger et al 2015), and research assessing population response to current drought conditions is important to inform future projections of sage-grouse populations. However for most species, the literature has focused on predicting potentially suitable habitats (e.g., species distribution surfaces) under various climate models (e.g., Hijmans andGraham 2006, Homer et al 2015).…”

Diverse landscapes, diverse risks: synthesis of the special issue on climate change and adaptive capacity in a hotter, drier Southwestern United States

“…Many studies have projected longer and unprecedented drought conditions (Ault et al 2014;Cayan et al 2010;Cook et al 2015;MacDonald 2010;Prein et al 2016;Seager et al 2007) and systemic pressures associated with additional stress on water supplies already near or beyond their natural limit in the future (Dettinger et al 2015). However, how humans will respond to decreased available water and the impacts at a local and a regional scale remain uncertain.…”

Vulnerability of California specialty crops to projected mid-century temperature changes

“…Much work has been done and is underway to assess how climate change will affect water resources in California and across the Southwest (CCTAG 2015;Dettinger et al 2015). Though predicted changes in the total amount of precipitation are currently equivocal, modeling studies consistently show that climate change will significantly increase potential evapotranspiration in California's specialty crop growing regions, and that changing irrigation practices can partly but not wholly compensate (Purkey et al 2008;Joyce et al 2011;Mehta et al 2013).…”