Large scale conversion of forest land to crop land weakening Indian Monsoon – IIT-B Study
Mumbai, August 24, 2016 :Changes and variability of Indian monsoon are traditionally linked to large scale atmospheric and oceanic circulations. Their association with local factors, such as, the recent changes of land use land cover are largely overlooked.
A study from Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay has revealed weakening of Indian monsoon in the North-Eastern and North-Central India due to large scale changes of land use land cover from forest land to crop land.
The study is published in Scientific Reports, by Nature Publishing Group (NPG). The work is led by Prof. Subimal Ghosh and Mr Supantha Paul from Interdisciplinary Program in Climate Studies, IIT Bombay.
Satellite data revealed large-scale changes of land use land cover (LULC) in India, specifically in terms of the conversion of forest land to crop land. Large-scale deforestation has been observed in India when the LULC map derived from Moderate Resolution Imaging Spectro-Radiometer (MODIS) for 2000s is compared with that derived from Advanced Very High Resolution Radiometer (AVHRR) for 1980s. The changes are visible in terms of significant decrease in the leaf area index, a term used to measure the green cover.
A regional simulation of Indian south-west monsoon with two different LULC of 1980s and 2000s, keeping all the large scale circulation same, reveals statistically significant reduction in monsoon rainfall over North-Central and North Eastern India with the changes in forest cover.
Large scale conversion of forest land to crop land resulted in conversion of deep-rooted vegetation to shallow-rooted vegetation that further reduces evapo-transpiration (ET), a local moisture source to precipitation. The precipitation that is being generated from local evapo-transpiration is known as recycled precipitation.
Prof. Subimal Ghosh mentioned, “Due to the large-scale deforestation, there is significant reduction in the recycled precipitation and hence in total precipitation. Our earlier study published in Journal of Hydrometeorology shows that the recycled precipitation is quite high in the North East and North-Central India. Impact of deforestation is quite prominent in those areas due to reduction in ET and recycled precipitation.” It should be noted that recycled precipitation contributes to around 25% of total monsoon precipitation during the end of the monsoon (August and September).
Work on the impact of large-scale LULC has significant implication in terms of generating rainfall projections for future to be used for climate change adaptation. Climate models are mostly forced with increasing Green House Gas emissions, largely ignoring the future possible changes in LULC. “For Indian monsoon, impacts of LULC change is critical and needs to be considered for regional projections and planning,” added Prof. Ghosh.
Recent studies show drying of Indian sub-continent due to warming of Western Indian Ocean. This condition would become more critical if deforestation continues at the present rate. This needs to be seriously considered in the development of national policy of regional climate change mitigation.
