Hydrology and Physiography of Groundwater and Wetland Habitats - Freshwater Ecology: Concepts and Environmental Applications - page 49

FIGURE 4.2 Global precipitation patterns. Mean monthly precipitation (in millimeters per
month) for 1998 (from the Global Precipitation Climatology Center).

spiration and evaporation together are called evapotranspiration . If water
is not lost to evapotranspiration, it infiltrates (flows down into) the soil and
can be stored as soil moisture (or as ice in polar or high-altitude areas). Wa-
ter that is not stored percolates down through the soil layers into ground-
water, flows across the surface, or flows through the shallow surface soils
to streams. The amount of precipitation required to cause runoff is greater
when the temperature is high because potential evapotranspiration is high.

FIGURE 4.3 The hydrologic cycle.