GLOBAL CHANGE AND WATER RESOURCES IN THE NEXT 100 YEARS

摘要

The economic, political, and scientific decision-making entities of U.S. society are in the midst of a continental-scale, multi-year experiment in the United States, in which we have not defined our testable hypotheses or set the duration and scope of the experiment, which poses major water-resources challenges for the 21st century. What are we doing? We are expanding population at three times the national growth rate in our most water-scarce region, the southwestern United States, where water stress is already great and modeling predicts decreased streamflow by the middle of this century. We are expanding irrigated agriculture from the west into the east, particularly to the southeastern states, where increased competition for ground and surface water has urban, agricultural, and environmental interests at odds, and increasingly, in court. We are expanding our consumption of pharmaceutical and personal care products to historic high levels and disposing them in surface and groundwater, through sewage treatment plants and individual septic systems. These substances are now detectable at very low concentrations and scientists have documented substantial effects on aquatic species, particularly on fish reproduction function. These are a few examples of our national-scale experiment.rnIn addition to these water resources challenges, over which we have some control, precipitation and streamflow patterns have been changing, and are predicted to change in coming decades, with western mid-latitude North America generally drier. Based on the instrumented record, hydrologists have already documented trends in more rain and less snow in western mountains. Hydrologists have documented earlier snowmelt peak spring runoff in northeastern and northwestern states, and western montane regions. Peak runoff is now about 2 weeks earlier than it was in the first half of the 20th century.rnDecision makers are now required to include fish and other aquatic species in negotiation over how much water to leave in the river, rather than, as in the past, how much water humans could remove from a river. Additionally, decision makers must pay attention to the quality of that water, including its temperature.rnSea level rise presents challenges for fresh water extraction from coastal aquifers as they are compromised by increased saline intrusion. A related problem faces users of 'run-of-the-river' water-supply intakes that are threatened by a salt front that migrates further upstream because of higher sea level.rnGlobal change and water resources challenges that we face this century include a combination of local and national management problems and evolving changes in climate that are already upon us. This set of challenges will continue and likely intensify as the non-climatic and climatic factors (such as predicted rising temperature and changes in the distribution of precipitation in time and space) continue to develop.