Pune Research Reveals Rain Evaporation During Monsoon
Pune: Scientists have quantified, for the first time in India, how much monsoon rainfall evaporates before reaching the ground, providing new insights that could significantly improve weather forecasting and climate modelling. The findings, produced through research conducted in Pune, indicate that nearly one-quarter of rainfall over the northern Western Ghats during the southwest monsoon never reaches the surface, highlighting an overlooked process that influences rainfall distribution and atmospheric behaviour.
The study represents an important advance in understanding India’s monsoon system, which underpins water security, agriculture, hydropower generation and urban planning. Researchers estimate that, on average, around 25 per cent of rainfall evaporates while falling through the atmosphere, although the proportion fluctuates considerably depending on daily weather conditions, ranging between 4 per cent and 61 per cent during the June-to-September monsoon period. The findings are expected to strengthen the accuracy of weather and climate models by improving the representation of below-cloud rainfall processes. Existing forecasting systems often struggle to account for how evaporating raindrops alter atmospheric temperature and air movement, factors that directly influence subsequent rainfall events. Scientists explained that as raindrops evaporate before reaching the ground, they absorb heat from the surrounding air, cooling the lower atmosphere. This process generates descending air currents and surface-level pools of cooler air, which can reshape cloud formation and affect the timing, location and intensity of future rainfall. More accurate representation of this interaction could improve forecasts of heavy rain, thunderstorms and monsoon variability.
To estimate the evaporation rate, researchers employed isotope analysis, a scientific technique that measures naturally occurring variations in water molecules. Because lighter water molecules evaporate more readily than heavier ones, the changing isotopic composition of rainfall provides a measurable record of how much evaporation has occurred during a raindrop’s descent. The research team collected rainwater and atmospheric moisture samples during the 2019 southwest monsoon and analysed them using laser-based instruments alongside atmospheric modelling techniques. According to researchers, the methodology provides India’s first direct observational estimate of rainfall evaporation and establishes a framework that can now be extended to different climatic regions across the country. Experts believe the phenomenon is likely to vary substantially between humid coastal belts, the Himalayan region and India’s arid interiors, where differences in temperature, humidity and rainfall intensity influence evaporation rates. Expanding the observation network nationwide could therefore improve regional forecasting while strengthening long-term climate projections.
Urban planners and water resource specialists increasingly rely on high-resolution rainfall forecasts to design resilient drainage systems, flood management infrastructure and reservoir operations. Improved understanding of rainfall evaporation could therefore support more effective planning for rapidly growing cities facing increasing climate uncertainty and more frequent extreme weather events. As India continues investing in advanced climate science, the research demonstrates how locally generated scientific evidence can enhance national forecasting capabilities. More precise modelling of rainfall evaporation is expected to strengthen disaster preparedness, water management strategies and climate resilience across urban and rural landscapes.
