Hydrologic effects of ecosystem response to climate change and land use change
Of all the ecosystem services, a sustainably supply of water may be the most important. Streamflow from forests alone provides two-thirds of the water supply in the United States, implying that water supplies depend entirely on a range of natural ecosystem types. Climate change, drought, outbreaks of insects and pathogens, wildfire, and ecological succession are altering ecosystems’ ability to provide abundant, clean water from the headwaters of our water supply systems. Simultaneously, public land management is changing in response to wildfire and endangered species concerns; private lands have undergone major changes in ownership and management; and native ecosystems have declined due to conversion to exurban development. While the near-term, local hydrologic effects of these changes are rather well understood, ongoing changes in ecosystems could have widely varying effects on sustainable water supplies to downstream areas. As a result, many regions face a difficult balancing act between further development, flood protection, water supply for urban areas and agriculture, and water releases for endangered species protection.
How will ongoing and projected changes in ecosystem conditions affect water supplies? Will earlier snowmelt reduce streamflow and produce droughts, especially in the west, or will these effects be more than counteracted by vegetation mortality and increased natural disturbances such as wildfire and insect outbreaks? What are the effects on ecosystem NPP of shifts in precipitation within and among seasons? How large are the likely effects of climate warming on ecosystem water use and water yield, compared to changes being wrought by new ecosystem management practices and exurban development? These topics are the subject of a workshop whose objectives are to (1) articulate the principles of ecosystem water use and how they respond to climate and disturbance drivers, (2) compare current trends in water yield across ecosystems and their responses to change, and (3) outline future studies needed to quantify water yield responses to contemporary changes in ecosystems.