Reduction in forest area has led to deficit rainfall, says IISc study
A recent study by researchers from the Indian Institute of Science (IISc) titled “Time-Series Modis Normalised Difference Vegetation Index (NDVI) based vegetation change analysis with land surface temperature and rainfall in Western Ghats, India” shows that because of change in landscape of north, central and southern Western Ghats, there is a decline in rainfall trend, which is also having an adverse impact on the food and water security.
The study, conducted by Prof T V Ramachandra, Centre for Ecological Sciences, IISc along with Uttam Kumar and Anandita Dasgupta, showed that the dense forest areas in the northern, central and southern Western Ghats have decreased by 2.84%, 4.38% and 5.77% respectively and agricultural or grasslands have increased by 2.23%, 4.32% and 5.85%.
The rainfall time-series data also showed a decreasing trend in the rainfall pattern from 2013 towards 2020 in the northern, central and southern Western Ghats, revealing a grave situation threatening water and food security in peninsular India with an increasing trend of deforestation. Also, the number of rainy days had decreased in the southern Western Ghats region.
The trends in rainfall time-series data were analysed using statistical methods and modelled using auto-regressive integrated moving average (ARIMA) which indicated a decreasing trend in the rainfall pattern, Ramachandra said.
There is also a marginal increase in human settlement or soil area and small decrease in the spatial extent of water bodies in all the three regions. The study also revealed that the temperature in dense forests has always been less than in agricultural or grassland areas in all the three seasons.
"We focused on vegetation data to investigate the distribution of land surface temperature and rainfall because the existing vegetation distribution is largely controlled by temperature and precipitation pattern. Monthly climatic changes and trends of the last 10 years provided a clear illustration of the NDVI trends,’’ he said.
Differences in NDVI–temperature and NDVI–precipitation correlations relative to vegetation types such as forest and agriculture or grassland were also investigated. This result supports and is of similar magnitude as temporal studies showing increase of NDVI corresponding to increase in growing season temperature over the length of the satellite record, Ramachandra added.