Rainfall

Rainfall is measured as depth (for example, millimetres) accumulated over a period, but the same total can arrive as a steady season-long drizzle or as a few intense storms, with very different effects on crops and soils. Distinguishing average annual rainfall from within-season distribution — how much falls during planting, flowering, or harvest windows — is essential to understanding its agricultural relevance.

Rainfed crops rely on rainfall, stored soil moisture, and, where practised, supplemental irrigation, to balance losses from evapotranspiration. Rainfall arriving during critical growth stages, such as germination, flowering, or grain fill, generally has more influence on yield than the same amount falling during less sensitive periods, which is one reason seasonal distribution matters as much as total rainfall.

Excess rainfall can saturate soils and cause waterlogging, leach nutrients below the root zone, delay field operations, and raise humidity in the crop canopy, favouring diseases such as downy mildew and gray mold. Insufficient rainfall reduces soil moisture available for germination, establishment, and growth, increasing reliance on stored soil water or irrigation.

• Irrigation to supplement rainfall shortfalls in dry periods or dry climates
• Drainage systems to remove excess water from saturated soils
• Crop and cultivar choice matched to typical local rainfall amount and seasonality
• Water harvesting and storage in regions with high rainfall variability

Rainfall is recorded using rain gauges and increasingly estimated using weather radar and satellite data, which help fill gaps between ground stations. Because rainfall varies substantially between nearby locations and from year to year, long-term averages alone are often insufficient for agricultural planning; local records and probability-based outlooks are commonly used alongside them.