Annual Rate Of Precipitation, Maryland And The District Of Columbia Have Similar Average Annual Precipitation Patterns

951 Words Aug 13th, 2015 4 Pages
Annual Rates of Precipitation
Maryland and the District of Columbia have similar average annual precipitation patterns (based on a period of 30 years from 1951-1980) with 42 inches and 43 inches, respectively. Although the precipitation pattern distributed evenly throughout the year, the spring and summer months (May – September) get approximately 2.5 inches more precipitation compared to the rest of the year (USGS, 1999). Furthermore, apart from the seasonal variation in the precipitation rates, there has been an increase in the annual precipitation rate of Washington, DC, since 1965 (see methods/discussion
Evapotranspiration
According to a USGS study, approximately one-third to one-half of total precipitation becomes runoff in central Maryland and the District of Columbia (USGS, 1999). Evapotranspiration makes up the difference between amounts of precipitation and runoff.
AET = P – Q
Where AET is actual evapotranspiration, P is the precipitation depth, and Q is runoff depth. Combined evaporation and transpiration from plants (evapotranspiration) is balanced by inflows as precipitation and outflows as runoff. Based on a research conducted by McGuiness (1963) for a period of seventeen years (1933-1949), the Rock Creek basin received an average precipitation of 43.5 inches, in which 12 inches was surface runoff. Therefore, if the precipitation and runoff values are substituted into the equation above, actual evapotranspiration rate of the basin equals 31.5 inches. However,…
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