The deficit of South-west monsoon in the country has grown from 10 per cent in the last week of August to 16 per cent during the first week of September. According to India Meteorological Department (IMD), the overall countrywide deficit has also risen from 3 to 4 per cent.
A latest study conducted by experts from IIT-Bombay has attributed large-scale deforestation in the country to the decline in rainfall, especially in North and North-east. Deforestation has resulted in a decline in evaporation of water through transpiration from plant surface. This in turn has lowered recycled precipitation that accounts for a quarter of rainfall during the last leg of the season.
The IMD experts, however, hope for a last bout of monsoon surge next week that could result in near to slightly above rainfall during the coming fortnight in parts of east and northeast India besides south Peninsula during the period. Simultaneously, rain is likely to take pace over many parts of central and adjoining north Peninsular India from September 12 onwards. Certain parts of North-West may also receive light rainfall during the same period.
The country has so far received 733.7 mm of rain as against the normal of 762.3 mm. Central India has registered the highest of 875.5 mm rain which is 3 per cent above average. On the other hand, North-east is reeling under the highest deficit of 14 per cent in the country, this season.
So far, the distribution of rainfall in the country has been fairly uneven. While Madhya Pradesh and Rajasthan have received nearly 25 per cent above normal rain, States like Gujarat, Punjab, Himachal Pradesh and parts of North-East have a deficit of nearly 20 per cent.
This baffling trend of rain has been explained in a study called “Weakening of Indian Summer Monsoon Rainfall due to Changes in land Use land Cover” undertaken by Interdisciplinary Programme in Climate Studies by the IIT-Bombay.
According to Dr Subimal Ghosh, lead author of the study, while monsoon is generally a product of large scale atmospheric circulation, local factors also play a role in its advance. “These include changes in land use and land cover that lead to changes in monsoon rainfall, which are in our hands, and because of them there has been a significant reduction in rainfall over two major regions, the Ganga basin and northeast India,” he says.
The study further found that both forest cover and monsoon rainfall declined considerably between 1980-1990 and 2000-2010.
The reduction in rainfall was especially pronounced in north and northeast India. The study’s models also showed that the large-scale conversion of forests to crop lands had resulted in a decline in the process by which moisture is transferred from soil and plants to the atmosphere.
The study explained that when there is a huge conversion of forest to farmland, there is a reduction in leaf area index, decreasing evaporation of water through foliage. In forests, the vegetation is deep-rooted, which can easily extract soil water, but crops have shallow roots and are unable to extract water that easily.