The water balance of the Susquehanna River Basin and its response to climate change

Historical precipitation, temperature and streamflow data for the Susquehan- na River Basin (SRB) are analyzed with the objective of developing simple statistical and water balance models of streamflow at the watershed'- s outlet. Annual streamflow is highly correlated with annual precipitation (r2 = 0.895) and, on a percent basis, changes in annual streamflow (Q) are about two times greater than changes in annual precipitation (P). Variations in P - Q, interpreted as annual evapotranspiration, are much smaller than variations in P and Q, and are weakly positively correlated with annual mean temperature in accordance with potential evapotranspiration formulae. Streamflow is monotonically related to diagnosed storage of water in the SRB from April through November. Deviations from this trend during winter are interpreted as changes in snowpack, and are in general agreement with climatological snow water equivalent estimates for the basin. A simple, spatially-lumped water balance model of the SRB is developed and shown to capture 99% of the mean annual cycle and 75% of the monthly streamflow from 1900 to 1987. Two "downscaled" predictions of precipitation and one of temperatu- re for a doubling of atmospheric CO2 are used as inputs to the statistical and water balance models of the SRB. The result is an annual streamflow increase of 24 + 13% (11.8 ± 6.7 cm).