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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 ...
In the equation, the change in water stored within the basin (ΔS) is related to precipitation (P) (water going into the basin), and evapotranspiration (ET), streamflow (Q), and groundwater recharge (D) (water leaving the basin). By rearranging the equation, ET can be estimated if values for the other variables are known:
The Penman equation describes evaporation (E) from an open water surface, and was developed by Howard Penman in 1948. Penman's equation requires daily mean temperature, wind speed, air pressure, and solar radiation to predict E. Simpler Hydrometeorological equations continue to be used where obtaining such data is impractical, to give comparable results within specific contexts, e.g. humid vs ...
The Penman-Monteith equation approximates net evapotranspiration (ET) from meteorological data as a replacement for direct measurement of evapotranspiration. The equation is widely used, and was derived by the United Nations Food and Agriculture Organization for modeling reference evapotranspiration ET 0 .
Given the limited data input to the equation, the calculated evapotranspiration should be regarded as only broadly accurate. Rather than a precise measure of evapotranspiration, the output of the equation is better thought of as providing an order of magnitude. [2] The inaccuracy of the equation is exacerbated by extreme variants of weather.
The conceptual model is used as the starting point for defining the important model components. The relationships between model components are then specified using algebraic equations, ordinary or partial differential equations, or integral equations. The model is then solved using analytical or numerical procedures.
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 leaving in the form of river discharge), or stored in the ground. This equation requires the system ...
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 ...