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Headwater-Dependent Systems: Definition, Drivers of Change and Potential Futures

Abstract:

Billions of people and critical ecosystems worldwide rely on headwaters. The temporal storage of atmospheric-source water provided by glaciers, seasonal snowpack, and upland groundwater, lakes, and wetlands--together with a variety of constructed reservoirs--plays a vital role in buffering hydrological extremes for humans and ecosystems, from the highlands down the freshwater gradient to the ocean. Changing climate, land use, and increasing demand for water alter the buffering capacity of headwaters and raise the likelihood of both irreversible ecological impacts and political conflict. To better understand and address these drivers, we must link social and ecological processes. However, we lack adequate data to understand these dynamics in most headwaters systems. Even the most basic assessments of water balances remain out of reach, let alone understanding how future climate extremes will affect …