Martonne aridity index

One expression of the combined influence of both precipitation and temperature is the de Martonne aridity index based on the formula... 

Thus, the Martonne aridity index defines not only climatic parameters but also vegetational ones. Seasonality of precipitation is another climatic factor that affects desert and steppe boundaries. For a given mean annual temperature, the boundary of a steppe will extend into wetter climates if its precipitation falls mainly in the summer. This is because summer evapotranspiration depletes soil moisture more thoroughly than winter evapotranspiration. For similar reasons, the size of a desert will be larger if its precipitation falls in the summer rather than in the winter (Monger et al., 2004). 

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See also in sourсe #XX -- [ , ]

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