PrecipitationEvapotranspiration

PrecipitationEvapotranspiration is a hydrological concept describing the relationship between atmospheric precipitation input to a surface and the losses due to evapotranspiration. In many studies, the term is used to discuss net water availability within a landscape, often expressed as effective rainfall, defined as P minus ET. When ET is greater than precipitation, soil moisture declines and water availability for runoff or recharge decreases.

Evapotranspiration comprises two components: evaporation from intercepted water, soil, and surface waters, and transpiration from plants. ET is influenced by solar radiation, air temperature, humidity, wind, soil moisture, and vegetation characteristics.

Controls on PrecipitationEvapotranspiration include climatic conditions, season, soil type, root depth, land cover, and crop coefficients. ET tends to increase with warmth and radiation if moisture is sufficient, but is limited by soil moisture deficits or stomatal regulation.

Measurement and estimation of PrecipitationEvapotranspiration rely on direct methods like lysimeters and eddy covariance for ET estimates, as well as weather data and remote sensing for large-scale assessments. Common modeling approaches include the Penman-Monteith method, while water balance methods compute P_eff from rainfall, ET, runoff, and infiltration.

Applications of the concept lie in water resources management, drought assessment, and irrigation planning, as well as climate impact studies. It helps gauge how much atmospheric input is actually available for soil moisture recharge, groundwater, and ecosystem needs, informing decisions in agriculture, urban planning, and environmental management.