Groundwater and baseflow drought responses to synthetic recharge stress tests

Abstract

Abstract. Groundwater is the main source of freshwater and maintains streamflow during drought. Potential future groundwater and baseflow drought hazards depend on the systems' sensitivity to altered recharge conditions. We performed groundwater model experiments using three different generic stress tests to estimate the groundwater and baseflow drought sensitivity to changes in recharge. The stress tests stem from a stakeholder co-design process that specifically followed the idea of altering known drought events from the past, i.e. asking whether altered recharge could have made a particular event worse. Across Germany, groundwater responses to the stress tests are highly heterogeneous, with groundwater heads in the north more sensitive to long-term recharge and in the Central German Uplands to short-term recharge variations. Baseflow droughts are generally more sensitive to intra-annual dynamics, and baseflow responses to the stress tests are smaller compared to the groundwater heads. The groundwater drought recovery time is mainly driven by the hydrogeological conditions, with slow (fast) recovery in the porous (fractured rock) aquifers. In general, a seasonal shift of recharge (i.e. less summer recharge and more winter recharge) will have lesser effects on groundwater and baseflow drought severity. A lengthening of dry spells might cause much stronger responses, especially in regions with slow groundwater response to precipitation. Water management may need to consider the spatially different sensitivities of the groundwater system and the potential for more severe groundwater droughts in the large porous aquifers following prolonged meteorological droughts, particularly in the context of climate change projections indicating stronger seasonality and more severe drought events.

Different drought types and the spatial variability in their hazard, impact, and propagation characteristics

“…An important question remains of what would have happened if a drought episode like 2018 started when storage in hydrological systems was low, i.e., a Type I + II episode. Stress tests or scenario studies can be used to explore the impacts of such worst-case episodes, as well as to prepare drought management for the future (e.g., Grecksch, 2019;Hellwig et al, 2021;Stoelzle et al, 2020).…”

Different drought types and the spatial variability in their hazard, impact, and propagation characteristics

“…An important question remains what would have happened when a drought episode like 2018 started when storages in hydrological systems were low, i.e., a Type I+II episode. Stress tests or scenario studies can be used to explore the impacts of such worst-case episodes as well as to prepare drought management for the future (e.g Grecksch, 2019;Hellwig et al, 2021;Stoelzle et al, 2020).…”

Early Warning Indicators of Groundwater Drought in Mountainous Regions

“…Groundwater drought occurs when groundwater recharge decreases, which is followed by a decrease in groundwater storage and, consequently, groundwater level (Van Loon, 2015). A decline in groundwater level can also lead to a reduction in groundwater discharge to streams (Hellwig and Stahl, 2018; Hellwig et al., 2021; Peters et al., 2005; Van Loon & Laaha, 2015) and springs (Laaha et al., 2016). These decreases can occur on different time scales, from months to years to decades due to the lag in response time of aquifers (Mishra & Singh, 2010; Van Lanen & Peters, 2000).…”