Delayed response of groundwater to multi-year meteorological droughts in the absence of anthropogenic management

Groundwater is a life-sustaining resource that supplies water to 2 billion people worldwide and is critical for agriculture. Despite the importance of groundwater, understanding of groundwater recovery from meteorological droughts is limited. Here, we utilize daily groundwater observations from unconfined aquifers without active groundwater management across the conterminous United States to illustrate that in response to a multi-year drought, it takes on average, 3 years for shallow aquifers to recover the storage lost during the drought. This recovery time increases with higher drought severity, and is influenced by the time-lag between the initiation (termination) of a meteorological drought and initiation (termination) of a groundwater drought. There is considerable variation in the time-lag duration, up to 15 years in some aquifers, controlled by geographic properties in regions with shallow water tables and precipitation characteristics in regions with deep water tables. A machine learning algorithm finds that the most important controls on the time-lag are the drought intensity at the beginning of the precipitation drought and the mean annual recharge. Projected increases in drought severity could potentially increase groundwater recovery times to droughts in a changing climate.

Automated summary

Groundwater is a crucial resource for 2 billion people worldwide and agriculture, but the understanding of its recovery from droughts is limited. Research shows it takes an average of 3 years for shallow aquifers to recover lost storage during multi-year droughts, a recovery time influenced by drought severity and time-lags between meteorological and groundwater droughts. Potential increases in drought severity due to climate change may prolong groundwater recovery times.