As the world’s largest distributed store of fresh water, ground water plays a central part in sustaining ecosystems and enabling human adaptation to climate variability and change. The strategic importance of ground water for global water and food security will probably intensify under climate change as more frequent and intense climate extremes (droughts and floods) increase variability in precipitation, soil moisture and surface water.

Groundwater recharge sustains the groundwater resources on which there is global dependence for drinking water and
irrigated agriculture. For many communities, groundwater is the only perennial source of water. Here, we present a newly
compiled 55-year record of groundwater-level observations in an aquifer of central Tanzania that reveals the highly episodic occurrence of recharge resulting from anomalously intense seasonal rainfall.