Groundwater Recharge within the Agricultural Landscape in a Changing Climate

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Summary The sustainable management of freshwater resources has become more challenging globally as a result of increasing demand, changes in land use and an uncertain climate. Quantifying the water balance is a fundamental component of watershed management with respect to the availability of clean water for both human and ecological use. A major component of the regional water balance is groundwater recharge, which directly controls the replenishment of subsurface reservoirs, the loading of surface contaminants and the timing and magnitude of surface water base flow. Due to the highly variable nature of groundwater recharge, it has been difficult to measure and quantify and is associated with a high degree of uncertainty. The magnitude, timing and spatial distribution of recharge is influenced by land use, topographic setting, subsurface geology and seasonal climatic conditions, particularly within rural regions where the majority of recharge occurs. With the increasing need to maximize crop production, agricultural drainage management is being implemented at a regional scale, including the installation of extensive tile drainage networks, which significantly influence the water balance within the agricultural landscape. In many northern countries, groundwater resources are extensively drawn from these rural regions, commonly from undulating glacial terrain where recharge patterns are complex. In addition, the impacts of climate warming are fundamentally influencing recharge dynamics in ways that are poorly understood. The proposed research program includes three main components. The first examines the interaction between tiles and the shallow groundwater flow system under a range of subsurface and climatic conditions with a specific focus on groundwater recharge. Detailed field investigations and legacy data sets will be integrated into advanced mathematical models to evaluate a wide range of scenarios designed the reveal the complex interaction between tile drains and the shallow subsurface. In the second component, the influence of depression focused recharge phenomena, which form following extreme precipitation events in low topographic settings, will be quantified through field investigations and advanced simulation tools to investigate the potential impact of these recharge phenomena on aquifer and public supply well vulnerability. The final component will integrate insight from the first two sections into a regional analysis of the combined influence of tile drainage, depression focused recharge and climate change on groundwater recharge with a specific emphasis on the regional water balance and the sustainability of groundwater resources. The overall results will assist water managers in understanding how the regional water balance is changing under the influence of managed agricultural drainage and climate change and inform future water management policy.