Water Resources Vegetation dynamics are tightly coupled with hydrologic processes. However, there is a broad range of possible outcomes among the six model scenarios, creating significant uncertainty in the risks that may arise. The Ohio and Tennessee valleys lie between regions of decreased moisture in the southeastern U.S., and regions of increased moisture in the northern U.S. and, therefore, the prospects are uncertain. Implications for shipping, irrigation, and domestic water uses would be profound. The Northwest, California, and the Great Basin could see large increases in runoff, primarily in winter, with the possibility of serious flooding.
Summer rains provide considerable input to both streams and vegetation.
If there is less vegetation, there is more runoff and vice versa. In areas with high winter rainfall, but dry summers, the runoff-vegetation relationship is quite complex. In addition, both vegetation and runoff can increase in the West. Runoff in the West is largely snowmelt dominated, and under a global warming scenario, generally increases in the winter. Under a moderate warming, there is still sufficient soil moisture recharge such that, with a longer growing season, forest growth may be enhanced.