IIT research teams study rainfall pattern of India to help frame long-term water policies

Using recorded rainfall data and simulation studies, the research team has gained insights that are critical not only to understand geographic variations in seasonal rainfall, but also to frame long-term water management policies.

Supported by the Max Planck Partner Group at IIT Madras, Department of Science and Technology and Ministry of Earth Sciences, the multi-institute team used rainfall data across the country over the past century to show the trends and variations in monsoon rains. The Indian summer monsoon that falls between June and September contributes approximately 80 per cent of the annual rainfall and plays a decisive role in the country’s agricultural output.

Sixty per cent of Indian agriculture depends on monsoon for irrigation, which in turn decides the economy as agriculture accounts for 18 per cent of India’s gross domestic product.

Recent observations, both at the meteorological level and local perceptions, show that monsoon has grown more unpredictable than before, which bodes ill for a country whose societal and economic wellbeing is critically linked to seasonal rains. Extreme events such as the floods in Kerala and the on-going zero-water situation in Tamil Nadu stand testimony to the recent vagaries of the Indian summer monsoon.

Dr Sachin S Gunthe, Associate Professor (Environmental and Water Resources Engineering Division), Department of Civil Engineering, IIT Madras, said, “The regional aspects of the Indian summer monsoon pattern are difficult to understand because it is affected by many factors. To discern rainfall patterns reliably, we (researchers) used IMDB’s daily rainfall data for the years 1901 to 2004 and performed simulations taking into consideration, phenomena such as maximum temperature, minimum temperature, rainfall and wind velocity. The model was validated with satellite-based observation from the European Space Agency- Climate Change Initiative (ESA-CCI) soil moisture data.”

It is common knowledge that geographic variation of extremes in rainfall occurs due to convection – the movement of moisture-laden hot air upwards, followed by cooling at higher altitudes and shedding of the moisture as rain. Convection-based rains would mean that regions with excess moisture in the air should experience more rainfall. This, however, was not seen in the rainfall pattern analysed by the research team.