Comparative analysis of impacts of groundwater droughts in a European context

Groundwater is of crucial importance for society, as it can uphold provision of hydrological services when there is a lack of water during drought. However, when droughts extend over longer periods of time and groundwater abstraction is increased, longer-lasting groundwater droughts can develop, aggravating existing water shortages and impacting groundwater-dependent environmental systems. This complex interaction means that groundwater contributes to mitigate droughts, but may also during longer droughts exacerbate drought hazards impacting society. In theory, it is understood that this interaction exists. However, to date no study used empirical data on how and when groundwater is factually reported as a mitigation agent or as an impact agent. In this study, we build on previous efforts to synthesize text-based reports on drought impacts in the European Drought Impact Inventory (EDII). We extended the EDII with additional, groundwater-related reports. We then analysed the EDII data to find out: a) how is society impacted by groundwater drought? b) how is groundwater used during drought? c) is the role of groundwater during drought different in different climatic or legislative settings? and d) did the role of groundwater during drought change over time? To answer these questions, we isolated the EDII reports that directly relate to groundwater, and mapped them onto new groundwater-related impact categories. We qualitatively summarized the way groundwater is reported as an impact, or as a mitigation agent, and provide statistics on the frequency of each occurrence. We further present the temporal development of the reporting, and compare the type and number of occurrence of groundwater-related reports between the UK, the Iberian Peninsula (Spain and Portugal) and the DACH region (Germany, Austria, Switzerland). The study provides the first systematic documentation of groundwater impacts and use during drought. It will thus provide guidance for researchers and water resource professionals considering whether groundwater can be used sustainably as an alternative resource during drought under different circumstances