An Indian Institute of Tropical Meteorology (IITM), Pune study estimates that about one-fourth of rainfall over the north-western Western Ghats evaporates before reaching the ground during the southwest monsoon. The finding matters because raindrop evaporation changes the heat and moisture balance below clouds and can influence the next rainfall cycle.
The study is presented as the first observational estimate of raindrop evaporation over India using an experiment-based approach. It uses isotope ratios in rainwater and atmospheric vapour, measured by laser spectrometry, to infer how much rain is lost in the air column before reaching the surface.
The estimate varies sharply by day and region, from about 4% to 61% across the four monsoon months of June to September. The study also says the 2019 monsoon data came from sampling rainwater and atmospheric vapour near Pune and feeding the results into a model that tracks evaporation of a single drop from cloud base to ground.
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