Bioclimatic Subhumid Zone of Russian Plains: Droughts, Desertification, and Land Degradation

Abstract

The boundaries of bioclimatic zones (semi-arid, dry subhumid, and subhumid) on the plains of Russia were determined according to the values 0.35, 0.50, and 0.75 of the aridity index (AI is the ratio between mean annual rainfall and potential evapotranspiration). The potential evapotranspiration was calculated by the Penman formula. The dry subhumid area (dry steppe landscapes) is located between isolines 0.35 < AI < 0.50, while the subhumid area (mainly steppe landscapes on the East European Plain and forest-steppe ones on the West Siberian Plain) is located between 0.50 < AI < 0.75. The subhumid area is characterized by the high frequency of atmospheric and soil-atmospheric droughts in some regions which may be assessed as episodically arid regions. The satellite indicator of land degradation (albedo) shows a significant positive degradation trend in the dry subhumid and semi-arid areas and an unstable positive trend in the subhumid area.