Groundwater and baseflow drought responses to synthetic recharge stress tests
2021
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.
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