Climatology of Monthly Runoff: Causality and Relations to Seasonality in Precipitation and Temperature

Observed monthly climatology of streamflows over the eastern United States showed significant differences from the month precipitation climatology. While the distribution of monthly precipitation is uniform throughout the year over the eastern United States (except peninsular Florida), the streamflow shows pronounced seasonality with peak flow seasons occurring during the winter over the Southeast and during the spring over the Mid-Atlantic and Northeast regions. A systematic analysis is carried out using simple water balance models that require no calibration for understanding the role of precipitation and temperature seasonality in influencing the streamflow seasonality. Preliminary findings show that for regions where precipitation and temperature are out of phase, streamflow seasonality index — which indicates the high flow season — occurs during the melt season. On the other hand, for regions where monthly distributions of precipitation is uniform, streamflow seasonality index typically coincide with storage seasonality.