Abstract: With the second highest percentage of farmland in the world, India was selected as the simulation experiment region to determine the impact and the mechanism of cropland expansion on regional climate. Based on global potential vegetation datasets and cropland dataset of HYDE V3, simulation experiments were conducted by using the Regional Integrated Environmental Model System (RIEMS) version 2.0 over potential vegetation and rainfed cropland areas of India. The results showed that, at the national scale, over the 10-year time period, the annual averaged air temperature increased by 0.1 ℃ and the precipitation rate decreased by 0.1 mm·d^-1 (12.8%). The climatic effect of cropland expansion varied in different climatic zones and different seasons in India. The temperature increased by 0.5-1.0 ℃ in subtropical humid region, 0.3-0.5 ℃ in semiarid and arid region, and decreased in tropical wet and dry region. The temperature increased by 0.2 ℃ in winter and 0.5 ℃ in pre-monsoon season and decreased by 0.5 ℃ in postmonsoon season, and there was no notable change in monsoon season. The subtropical humid region, semiarid and arid regions saw the notable decreased precipitation, and dry season saw the decreased precipitation, with the largest of 0.3 mm·d^-1 in the premonsoon season. The increased sensible heat flux, the decreased latent heat flux and the downward flow due to the divergence circulation at 850 hPa resulting from the rainfed cropland expansion can give the reasonable explanation for the increased temperature and decreased precipitation.

Key words: ecosystem engineer, soil microbe, nutrient cycling, soil biological fertility.