Water vapour radiation over the Himalayas has been mainly responsible for the rise in temperature in the High Altitude Himalayas region, said a study conducted by Indian scientists at Hanle in Ladakh (western Trans Himalaya) and Nainital (a part of central Himalayas) in Uttrakhand.
According to these scientists, a combination of aerosols (fine solid or liquid particles in gas smoke, fog, and mist) and water ‘vapour radiative effects’ over the Himalayan range is specifically important for regional climate. It highlights the importance of water vapour as a key greenhouse gas and climate forcing agent over the Himalayan region, a ministry of Science and Technology note here stated.
The research led by Umesh Chandra Dumka from Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, an autonomous research institute of the Department of Science and Technology (DST) showed that Precipitable Water Vapour (PWV) exhibits a positive radiative effect at the top of the atmosphere (TOA) in high altitude remote locations.
The effect of vapour radiation has been in the order of about 10 watts per square metre (W m-2) at Nainital at an altitude of 2200m in Central Himalaya, and 7.4 Wm-2 at Hanle at an altitude of 4500 meters in western Trans Himalaya. Team members from the National Observatory of Athens (NOA), Greece; Tohoku University, Japan; Indian Institute of Astrophysics (IIA) and CSIR Fourth Paradigm Institute (CSIR-4PI), Bengaluru and Institute for Advanced Sustainability Studies, Germany also contributed to the study.
The research published in the Journal of Atmospheric Pollution Research, Elsevier has shown that the atmospheric radiative effect due to precipitable water vapour PWV is about 3-4 times higher compared to aerosols, resulting in atmospheric heating rates of 0.94 and 0.96 K Day-1 at Nainital and Hanle, respectively. The results highlight the importance of PWV and aerosol radiative effects in the climate-sensitive Himalayan region, according to the ministry.