Water scarcity as a driver of multiple stressor effects

Abstract

Growing human demands for water are leading to rapid increases in the frequency and severity of water scarcity, where there is insufficient water to simultaneously support both human and ecosystem water needs. Water scarcity is most often caused by limited water availability, and it is thus in arid and semiarid regions with high water demands where the problems are most acute. Within these climate zones, evapotranspiration exceeds rainfall in most years, and thus the hydrologic regime of rivers often includes prolonged periods with low or zero flows. Water scarcity can greatly exacerbate the frequency and severity of low flows, amplifying a range of potentially interacting stressors, including habitat loss, water quality declines, and increased biotic interactions that alter aquatic biota and ecosystem processes. Thus, despite many plants and animals displaying specific physiological and life-history adaptations that equip them to persist in arid ecosystems, water scarcity poses a growing threat in maintaining the structure and functioning of river environments. In this chapter, we seek to summarize the major interacting stressors that arise from water scarcity in arid and semiarid landscapes, especially the effects of habitat loss, declining water quality, and increased biological interactions. We consider both impacts their mechanistic pathways and emphasize the potential interactions with other drivers, such as land use change, in affecting riverine ecosystems. We draw on a two different case studies to demonstrate interactions between multiple stressors in these systems, as well as summarize potential mitigation strategies and future research needs.