Hydrogeological Drought

Background

Hydrogeological drought refers to a prolonged period of abnormally low groundwater levels resulting from reduced recharge due to extended meteorological and hydrological droughts. Unlike surface water droughts, hydrogeological droughts develop more slowly but can persist longer due to the delayed response of groundwater systems to changes in precipitation. To monitor and quantify hydrogeological drought conditions, several indices have been developed, among which the Groundwater Resource Index (GRI) and the Groundwater Wetness Index (GWI) are widely used: Groundwater Resource Index (GRI): The GRI is a standardized measure that evaluates groundwater availability relative to historical conditions. It is typically based on deviations from long-term mean groundwater levels, enabling consistent assessment across regions and time periods. Groundwater Wetness Index (GWI): The GWI quantifies groundwater wetness relative to a historical baseline, often incorporating a percentile-based approach. Lower GWI values indicate drier-than-normal conditions, making it a useful tool for identifying and tracking drought severity and recovery. These indices support early warning systems, resource management decisions, and long-term planning in water-scarce regions, highlighting the importance of groundwater monitoring in an era of increasing climatic variability.