Changes of aridity indices in Mongolia

Aridity is one of the major indicators to delineate territories prone to desertification, thus the present paper discusses spatial and temporal variability of aridity in the past over the Mongolia. The aridity were calculated using four temperature and precipitation based indices: 1) de Martonne aridity index (IDM); 2) Thomthwaite aridity index (AI); 3) moisture coefficient by VI. Mezentsev (MI) and 4) Hydrothermal coefficient by Selyaninov (HTC). The basic meteorological data from 70 stations in Mongolia for the period of 1961-2015 are used in present paper. The area of drylands (hyper-arid, arid, semi-arid and subhumid regions) is different depending on used index. According to the results drylands delineated by IDM, MI, AI and HTC is 64.1%, 70.7%, 85%, and 98%, respectively. Out of 4 aridity indices, AI and MI showed high correlation with NDVI derived dryland regions. According to the temporal analysis of AI and MI around 66% of a time series had a decreasing tendency during observed period of time. The central and northeastern regions of the country have the significant decreasing trends of the aridity indices. The relative changes of the aridity indices vary between 14%-74% for stations with significant decreasing trend.