Evapotranspiration is defined as the evaporation lost from moisture on the soil surface, and the transpiration of plants whose roots tap moisture below the surface.
Figure 21(JPEG) provides an example of monthly evapotranspiration and precipitation in Plum Creek sub-watershed. As expected, highest evapotranspiration rates occur in summer months, while rainfall lows occur in summer months. Peak increases in precipitation are observed in spring and fall months.
Blanco Water Atlas 
