Using soil moisture observation to assess karstic groundwater recharg

Abstract:

In the context of climate change, pressure on karst groundwater resources is increasing, leading to the need for an improved water management. The surface of the karst systems was shown to play an important role for recharge processes that replenish karst aquifers. However, the soils of karst systems have received little attention in karst system characterization, since karst systems are usually analyzed through the output signal measured at the system outlet (the karst spring). In this study, we developed a method to explore the role of soil moisture dynamics in generating groundwater recharge by using a large number of soil moisture measurements at a test site at Southwest Germany. Including observations of climate, soil moisture (15 profiles, at 10cm and 20cm depth, distributed across forest and grassland), and discharge, we extract individual precipitation, soil moisture, and recharge events. We show thata large fraction of precipitation events does not lead to recharge event and that around a third of the soil moisture events leads to recharge. The best predictions of the fractions of precipitation that becomes recharge for the extracted events are obtained with soil moisture observations from deeper probes (20cm in our case) located at the grassland where evapotranspiration processes and root water uptake of the shallow rooting systems are less pronounced. Based on observations from the surface of karst systems, our new approach provides new and reliable insights to characterize the controls and temporal dynamics of groundwater recharge in karst regions. It can be applied to any other sites where observations of climate and soil moisture are available.