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

Abstract

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.