Ecohydrology and Climate Change in the Mountains of the Western USA – A Review of Research and Opportunities

Abstract

Snow‐dominated mountain regions are strategic providers of water resources and ecosystem services. They are also likely to be highly vulnerable to a warming climate. In this review, we argue that an ecohydrologic perspective is critical for understanding changes that are already occurring and ultimately for predicting future vulnerabilities in both water resources and ecosystem health. We focus our review on the relatively well‐studied mountains of the Western USA. In this region, observations and models show significant climate‐driven changes to hydrologic processes including changes to snow accumulation and melt, evapotranspiration, soil moisture, and streamflow. At the same time, there is growing evidence of climate‐driven changes in vegetation structure and function. We summarize these studies and discuss how changes in hydrology interact with changes in terrestrial ecosystems to lead to complex and sometime synergistic responses. We conclude by identifying research needs to be addressed by emerging monitoring and synthesis networks that focus on the ecohydrology of mountain environments within a changing climate.

Mountain runoff vulnerability to increased evapotranspiration with vegetation expansion

“…This discrepancy is attributable to two phenomena that have received little research attention in the Sierra Nevada and that hydrologic models are struggling to represent (5,8,9). The first issue is obvious: models have assumed the distribution of vegetation type and density will remain static (10-13), whereas there is consensus in the ecological literature that upslope redistribution is likely and may have already begun (4, 15, 16, 26, 27).…”

“…River flow (Q) is a function of precipitation (P) minus evapotranspiration (ET) (P−ET); increased montane ET with warming, either because of the direct effect of temperature on evaporative demand or the indirect effect of warming on vegetation density and distribution, would reduce Q (5,(7)(8)(9). However, hydrologic model projections for California's Sierra Nevada have discounted this possibility, indicating little or no effect of warming on annual ET (10)(11)(12)(13).…”

“…water resources | plant migration R oughly 4 billion people globally and 20 million people in the state of California rely on mountain runoff for freshwater, and there is growing concern these water resources will prove vulnerable to climate change (1)(2)(3)(4)(5)(6). River flow (Q) is a function of precipitation (P) minus evapotranspiration (ET) (P−ET); increased montane ET with warming, either because of the direct effect of temperature on evaporative demand or the indirect effect of warming on vegetation density and distribution, would reduce Q (5,(7)(8)(9).…”

Integration of hydrological and economic approaches to water and land management in Mediterranean climates: an initial case study in agriculture

“…Ceballos et al (2008) find a similar situation in the nearby Duero Basin. In the same vein, although for different reasons, Hoff (2006) on a global scale, and Tague and Dugger (2010) …”

Spatial Heterogeneity in Sensitivity of Evapotranspiration to Climate Change

“…The link between climate change and hydrological response is one of the main questions to be researched in the past and even today in hydrology. Many attempts have been made to formulate the mean annual water-energy balance [11][12][13][14]. Budyko (1974) assumed that the actual evapotranspiration is a function of the aridity index and precipitation, and it can be expressed as E/P=f(E 0 /P) [15].…”