Drought

• Meteorological drought — a shortfall in precipitation compared with the long-term normal for a location and season.
• Agricultural drought — insufficient soil moisture to meet crop, pasture, or forage water requirements, which can develop even during a relatively short precipitation gap if evaporative demand is high.
• Hydrological drought — reduced streamflow, groundwater levels, or reservoir storage, which typically develops and recovers more slowly than the other forms.

These forms interact and can occur in different combinations depending on regional climate, water infrastructure, and land use.

Crop growth depends on a continuous supply of soil moisture to support cell expansion, nutrient uptake, and photosynthesis. When moisture becomes limiting, plants may close stomata to conserve water, which also reduces carbon dioxide uptake and photosynthesis; if the deficit persists, especially during sensitive stages such as flowering and grain fill, yield and quality can decline substantially. The specific sensitivity of a crop to drought depends on its species, growth stage, root system, and the local soil’s water-holding capacity.

Beyond direct crop impacts, drought reduces pasture and forage growth for grazing livestock and can lower the quality and quantity of available feed and water. Extended dry periods can also increase soil erosion risk once vegetation cover thins, elevate wildfire risk in some landscapes, and place pressure on irrigation water supplies shared across users.

• Efficient irrigation methods, such as drip or sprinkler systems, that reduce water losses
• Soil management practices that improve water infiltration and retention, such as maintaining organic matter and reducing compaction
• Drought-tolerant or shorter-season crop varieties suited to the local climate
• Conservation agriculture and residue retention to reduce evaporative losses and protect soil structure
• Water-use planning and scheduling that prioritise critical crop growth stages

National meteorological and agricultural agencies track drought using combinations of precipitation records, soil-moisture data, streamflow and reservoir levels, and satellite-derived vegetation indices, often summarised through standard drought indices and early-warning services. These tools support decisions on water allocation, planting, and, where available, drought relief programmes, though specific indices and thresholds vary by country and agency.