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The GPCC drought index provides SPEI datasets at a 1.0° spatial resolution for limited timescales (1, 3, 6, 9, 12, 24, and 48 months). [5] Inputs to SPEI datasets can include high-resolution potential evapotranspiration (PET) from the Global Land Evaporation Amsterdam Model (GLEAM) and hourly Potential Evapotranspiration (hPET). GLEAM is a set ...
Evapotranspiration is typically measured in millimeters of water (i.e. volume of water moved per unit area of the Earth's surface) in a set unit of time. [6]: Ch. 1, "Units" Globally, it is estimated that on average between three-fifths and three-quarters of land precipitation is returned to the atmosphere via evapotranspiration.
ET is evapotranspiration Δ S is the change in storage (in soil or the bedrock / groundwater ) This equation uses the principles of conservation of mass in a closed system, whereby any water entering a system (via precipitation), must be transferred into either evaporation, transpiration, surface runoff (eventually reaching the channel and ...
In 1948, C. W. Thornthwaite proposed an AI defined as: = where the water deficiency is calculated as the sum of the monthly differences between precipitation and potential evapotranspiration for those months when the normal precipitation is less than the normal evapotranspiration; and where stands for the sum of monthly values of potential evapotranspiration for the deficient months (after ...
In agriculture, this is called a crop coefficient. The difference between potential evapotranspiration and actual precipitation is used in irrigation scheduling. Average annual potential evapotranspiration is often compared to average annual precipitation, the symbol for which is P. The ratio of the two, P/PET, is the aridity index.
Drylands are zones where precipitation is balanced by evaporation from surfaces and by transpiration by plants (evapotranspiration). [1] The United Nations Environment Program defines drylands as tropical and temperate areas with an aridity index of less than 0.65. [2] One can classify drylands into four sub-types: Dry sub-humid lands; Semi ...
Palmer drought index (sometimes called the Palmer drought severity index (PDSI)): a regional drought index commonly used for monitoring drought events and studying areal extent and severity of drought episodes. [28] The index uses precipitation and temperature data to study moisture supply and demand using a simple water balance model. [28] [29 ...
The hydrological cycle is a system whereby the evaporation of moisture in one place leads to precipitation (rain or snow) in another place. For example, evaporation always exceeds precipitation over the oceans. This allows moisture to be transported by the atmosphere from the oceans onto land where precipitation exceeds evapotranspiration.