A study by the Advanced Centre for Atmospheric Radar Research at the Cochin University of Science and Technology (Cusat) has said that summer rainfall is significantly controlled by convection, and the increasing trend of rainfall and intensity directly reveals the strengthening of deep convection during the recent epoch.
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The study, published in the Nature Portfolio Journal (NPJ), reported a shallow to deep transformation in cloud depth over the west coast of India during the past four decades. The results suggest an ice-rich cloud population in the recent decade, which is indicative of an increasingly convective character of rain-making processes over the west coast.
The study was done by Sreenath A.V. under the guidance of S. Abhilash, Director, Advanced Centre for Atmospheric Radar Research.
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It pointed out that during the monsoon season, low clouds were generally seen on the west of the Western Ghats. However, in recent years, clouds of 12 km to 14 km in height were formed during the monsoon season, causing thunderstorms. When such clouds rise to a thickness of 1 km to 14 km, they act as a ‘water tank’ above the surface and heavy rains over a short time, leading to flooding.
The study said more humidity in the atmosphere caused more heavy rainfall, but the heavy rainfall did no good to water sources and the agriculture sector. Heavy rainfall over a short time could cause water to run off quickly, and, as a result, nutrients in the topsoil were lost quickly. It will also lead to more flooding in cities, and the current unsustainable drainage system across Indian cities will not be able to withstand heavy rains.
The study pointed out a few important factors that led to the change in rainy season, the first being the alarming rise in surface temperature of the Arabian Sea off the west coast. Coastal South Asian summer monsoon circulation and the associated increase in south-westerly winds were the other factors influencing the change in rainfall pattern.