ABSTRACT
Precipitation and runoff are critical variables in the hydrologic cycle. Many variables determine the patterns of precipitation that occur within any one continent. These include latitude, altitude, and distance of the location in question from the ocean. At any one place the following conditions are necessary for precipitation to occur: an air mass of sufficient humidity must exist; the air mass must be cooled to a dew point temperature; and cloud droplets must grow considerably in size. Predictions of longer-term precipitation, runoff, and stream flood flow are important in dam construction. Precipitation furnishes the main source of recharge for wellfield aquifers. In hydrologic practice the term precipitation is restricted primarily to consideration of either snow or rain. Rainfall is the most important source of precipitation in most areas and thus the main contributor to runoff, stream flow, and aquifer recharge.
