How a drought develops

Drought propagates through the water system in stages, each lagging the last. A rainfall deficit takes months to become a groundwater deficit — and years to recover from one.

Why the lag matters: A wet month can end a meteorological drought while reservoirs and aquifers remain badly depleted. Headlines about rain "ending the drought" usually refer only to the first stage.
Winter rainfall: Groundwater recharges almost entirely in winter, when evaporation is low. Summer rain largely evaporates or is taken up by plants and does very little for aquifers.

Text description

A sequence of four drought types. A rainfall deficit produces meteorological drought within weeks. Soil moisture then falls, producing agricultural drought within months. River flows and reservoir storage decline next, producing hydrological drought. Finally groundwater levels fall, producing groundwater drought, which takes the longest to develop and the longest to recover. Restrictions are applied at different points along this sequence.