GROUNDWATER-RECHARGE RESPONSE TO TEMPORAL VARIABILITY OF PRECIPITATION IN A PRAIRIE WATERSHED

Groundwater recharge sets a constraint on aquifer water balance in the context of water management. Multi-decadal data on groundwater and other relevant hydrological processes can be used to understand the effects of climatic variability on recharge, but such data sets are rare. The climate of the Canadian prairies is characterized by large inter-annual and inter-decadal variability in precipitation, which provides opportunities to examine the response of groundwater recharge to changes in meteorological conditions. We conducted a decadal study in a small (250 km²) prairie watershed in Alberta, Canada. Relative magnitude of annual recharge, indicated by water-level rise, was significantly correlated with a combination of growing-season precipitation and snowmelt runoff, which drives depression-focussed infiltration of melt water. Annual precipitation was greater than vapour flux at an experimental site in some years and smaller in other years. On average precipitation minus vapour flux was 10 mm/y, which was comparable to the magnitude of watershed-scale groundwater recharge estimated from creek baseflow. Average baseflow showed a distinct shift from a low value (4 mm/y) in 1982-1995 to a high value (15 mm/y) in 2003-2013, indicating the sensitivity of groundwater recharge to a decadal-scale variability of meteorological conditions. These findings provide useful insights into the future recharge regime in the prairie region under projected changes in air temperature and precipitation.