that we've come to expect here in the United States—the inexpensive food supplies—may not continue.

Since the beginning of the industrial revolution, the abundance of carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, and other gases in the atmosphere has increased. The buildup of these gases may alter global temperatures, the worldwide distribution of precipitation, and the quantity and quality of our water resources—all of which impact the productivity of our crop land, range land, and forest land. Yet, agriculture is not only impacted by environmental change, it is also a cause of that change. A recent EPA report shows, for example, that agriculture contributed an estimated 26 percent to the increase in atmospheric gases in the 1980s; agriculture accounted for 13 of the 18 percent increase in atmospheric methane. Ruminant animals, rice paddies, fertilizers, cultivated natural soils, biomass burning, and land use conversion are all sources of agriculture's contribution to environmental change.

Though we know agriculture is contributing to the increase in atmospheric gases, our understanding of the links between agriculture and climate variability is still limited. Understanding how agriculture affects and is affected by environmental change requires improved understanding of basic hydrologic processes and improved water supply forecasting techniques.

We need to improve our quantitative understanding of basic hydrologic processes: ground water recharge, snow accumulation, rainfall variations with elevation, evaporation, and how all of these processes influence streamflow. We also need to develop improved fundamental process models that link appropriate hydrologic processes to relative factors in environmental change.

We need improved predictions of future water supplies. We need to improve the accuracy of water supply forecast models through new developments in hydrologic process models and new technologies, such as remote sensing, geographic information sys-