SEASONALITY OF RECHARGE MECHANISMS IN THE BASIN AND RANGE OF NORTH AMERICA

The Basin and Range Province of western North America extends across almost 20 degrees of latitude. As a result the climate and in particular the seasonality of precipitation varies significantly across this region. Here, we provide an overview of the variability of recharge mechanisms as affected by climate in parts of this region. Work in southern Arizona where the seasonal distribution of precipitation is roughly equal between summer and winter has demonstrated that summer precipitation is less effective than winter precipitation at being transformed into Mountain System Recharge (MSR). In the Tucson basin less than 10% of MSR originates from summer precipitation while in the San Pedro basin summer precipitation is nearly 25% of MSR. Despite the small contribution of summer precipitation to recharge, in both the San Pedro basin in Arizona and the San Miguel basin of central Sonora Mexico flood driven recharge during summer monsoon season also plays a significant role in overall basin recharge. However the mechanisms of flood recharge processes are different in these basins. In the San Miguel this flood driven recharge originates in mountains while in the San Pedro it originates from valley bottom infiltration excess overland flow. This work focused on the southern extent of the Basin and Range offers a window into how processes in the Basin and Range might change under prospective climate change. Some simulations of climate impacts on groundwater recharge show the importance of winter conditions across the region and the currently available data on the seasonality of recharge across the region indicates a significant susceptibility to changes in winter temperatures and precipitation.