The most direct impact of global climate change on agricultural water supply is its alteration of climate change. Changes will occur in average annual amount, temporal distribution, and intensity and duration of individual events. The effects will be felt directly, in the case of rainfed agriculture, and indirectly, through their effect on watershed hydrology and runoff, in the case of irrigated agriculture. Higher global temperatures will evaporate more water and increase the moisture-holding capacity of the atmosphere. Annual precipitation will increase in some areas and decrease in others. In general, areas which are already humid will receive more rainfall and already dry areas will receive less. Regional climate models can provide more detailed predictions, but their resolution is still relatively coarse. Worldwide, the expectation is for more intense precipitation events and longer dry periods between events.
