Annual rainfall refers to the total amount of precipitation, including rain, snow, sleet, and hail, that a specific location receives over the course of a year. It is typically measured in millimetres (mm) or inches, with millimetres being the standard unit in most scientific and environmental studies. Rainfall is captured using rain gauges, which collect the water and measure its depth. In meteorology and hydrology, the annual rainfall figure is crucial because it provides insights into the climate patterns of a region, as well as its seasonal and yearly variability. This measurement can vary significantly across different geographical regions due to factors like altitude, proximity to water bodies, prevailing winds, and weather patterns. For instance, tropical rainforests receive high annual rainfall, while deserts experience very low amounts.