B1. Recession Slope Analysis Coefficients, Low Flows, Groundwater and Precipitation Responses for Climate Change Studies

Recession slope analysis has often been used to estimate aquifer thickness, i.e. groundwater depth. Here we look at long term trends in the coefficients of this analysis for several large watersheds in areas potentially free of human influences in Pennsylvania, and compare them with trends in groundwater depths and low flows. We also look at long term precipitation trends in these areas, making the effort to compare the trends according to different hydrological units such as individual watersheds and Atlantic/non-Atlantic interferences drainage areas. In general total annual precipitation has tended to increase. These increases are matched by an increase in low flows. Intriguingly, the coefficients of the recession slope analysis show trends that do not match the trends in groundwater depths or low flows. These comparisons show that the choice of analysis may have important implications on the conclusions drawn from studies that attempt to assess the effects of climate change on the hydrological cycle.