better year-round erosion protection will likely produce fewer negative water impacts.

Understanding water quantity impacts is dependent on understanding the agricultural water cycle depicted in Figure 1-1. Crops can be either rainfed or irrigated (see Figure 1-2). Irrigation water can come from groundwater or surface water, and groundwater can be withdrawn from either a surficial aquifer (connected directly to the surface) or a confined aquifer (overlain by a low permeability layer, or aquitard, such as clay). Some of

FIGURE 1-1 The agricultural water cycle. Inputs to a crop include rainfall and irrigation from surface water and groundwater. Some water is “consumed” (that is, incorporated in the crop or evapotranspired), some returns to surface waterbodies for human or ecological use downstream, and some infiltrates into the ground. Copyright by the International Mapping Associates.