Droughts

Droughts are prolonged deficient precipitation causing water shortages across natural and human systems. They are not a single phenomenon; they involve meteorological drought, agricultural drought, hydrological drought, and socioeconomic drought, and are influenced by both natural variability and longer-term climate trends. Droughts differ in severity, duration, extent, and timing.

Causes: Natural variability (El Niño/La Niña, atmospheric circulation patterns) and climate change. Human factors such as land-use changes, groundwater depletion, irrigation, and deforestation can exacerbate drought impacts. Drought onset can be abrupt or slow.

Measurement and monitoring: Drought assessment uses indices such as the Palmer Drought Severity Index (PDSI), Standardized Precipitation Index (SPI), and SPEI. Hydrological drought is often evaluated by river discharge and reservoir storage. Droughts are commonly categorized with watches, warnings, or alerts based on thresholds and forecast information. Monitoring networks track precipitation, soil moisture, streamflow, and groundwater levels to inform decision making.

Impacts: Droughts affect agriculture and livestock, reduce household and industrial water supplies, limit power generation, stress ecosystems, increase wildfire risk, and raise economic costs and food security concerns. Vulnerability is shaped by regional water resources, governance, and adaptive capacity.

Management and adaptation: Drought risk management includes preparedness, early warning systems, and drought contingency plans; improving water-use efficiency and irrigation practices; sustainable groundwater management; reservoir operation and drought-relief strategies; and demand restrictions. Long-term adaptation emphasizes integrated water resources management, diversification of water supply, rainwater harvesting, and, where feasible, desalination. Cooperation across sectors and regions supports resilience to variable and changing precipitation patterns.