NEGATIVE FEEDBACK TO CLIMATE WARMING: HOW SHIFTS IN RECHARGE TIMING CAN AFFECT SHALLOW GROUNDWATER TEMPERATURE, KONZA PRAIRIE LTER SITE, NORTHEASTERN KANSAS

Climate change is expected to result in warming of shallow groundwater systems due to predicted increases in mean annual temperatures across much of the globe. However, the changes in timing and intensity of precipitation predicted to occur in many regions may have a stronger control over groundwater temperature. We present results of 8 years of high-intensity (5 minute) groundwater temperature monitoring at the Konza Tallgrass Prairie LTER Site in northeastern Kansas, where variations in precipitation patterns have a stronger influence over groundwater temperature than variations in mean annual air temperature. This temperate-climate, mesic grassland, where 1- to 2-meter thick limestone aquifers alternate with thicker shales, may be representative of a large region: grasslands cover one-fourth of the continental land area and the microkarst geology is representative of approximately one-third of the contiguous United States. Temperature of shallow groundwater at the Konza Prairie (2005-2013) is not strongly correlated with air temperature. Instead, groundwater temperature is predominantly controlled by precipitation timing and intensity, which has recently resulted in increased cool-season recharge. Groundwater recharge is dependent upon many factors, including precipitation intensity and evapotranspiration. As such, precipitation in the warm season may not necessarily recharge the aquifer, but may be transferred to the atmosphere or vegetation, or may become runoff when the precipitation rate exceeds infiltration capacity. We propose that increases in cool-season precipitation quantity and intensity (with little to no change in annual precipitation amounts), as predicted for this region by the 5^th Climate Change Assessment by IPCC, will cause cooling of shallow groundwater and subsequent discharge to stream water, creating a negative feedback to climate warming.