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The Standardized Precipitation Evapotranspiration Index (SPEI) is a multiscalar drought index based on climatic data. It was developed by Vicente-Serrano et al. (2010) at the Institute Pirenaico de Ecologia in Zaragoza, Spain. [1]
Similarly to precipitation effectiveness, Thornthwaite also developed a T/E index to represent thermal efficiency. Featuring six climate provinces: Tropical, mesothermal, microthermal, taiga, tundra and frost. [3] [5] The T-E index is the sum of the 12 monthly T-E ratios, which can be calculated as:
Potential evapotranspiration is expressed in terms of a depth of water or soil moisture percentage. If the actual evapotranspiration is considered the net result of atmospheric demand for moisture from a surface and the ability of the surface to supply moisture, then PET is a measure of the demand side (also called evaporative demand).
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 ...
Studies suggest that precipitation effectiveness (PE) within the Thornthwaite moisture index is overestimated in the summer and underestimated in the winter. [34] This index can be effectively used to determine the number of herbivore and mammal species numbers within a given area. [35] The index is also used in studies of climate change. [34]
Standardized Precipitation Evapotranspiration Index (SPEI): a multiscalar drought index based on climatic data. The SPEI accounts also for the role of the increased atmospheric evaporative demand on drought severity. [27] Evaporative demand is particularly dominant during periods of precipitation deficit.
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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. A humid subtropical climate is a zone of climate with hot and humid summers, and cold to mild winters.