Understanding the Effects of Water Vapour in the High Altitude Himalayas
Recent studies have suggested an increase in overall warming in the High Altitude Himalayas as a result of the positive radiative effect exhibited by water vapour at the Top of the Atmosphere (TOA). This article delves into the key aspects of this development, examining what water vapour is, its significance, and the findings of the research.
About Water Vapour
Water vapour represents the state of water when in the hydrosphere, achieved through evaporation, boiling of water, or sublimation of ice. Considered the most dominant greenhouse gas, water vapour accounts for 95% of greenhouse gases. Increased levels of carbon dioxide escalate water vapour, which subsequently leads to warmer temperatures.
The Significance of Water Vapour
Playing a dominant role in the radiative balance and the hydrological cycle, water vapour stands out as a principal element in the thermodynamics of the atmosphere. It contributes to absorption and emission in numerous bands and condenses into clouds that reflect and absorb solar radiation, thereby directly impacting energy balance.
What Does the Recent Research Say?
The research reveals that the atmospheric radiative effect due to Precipitable Water Vapour (PWV) is about 3-4 times higher compared to aerosols. This results in atmospheric heating rates of 0.94 and 0.96 K Day-1 at Nainital and Hanle, respectively. The study underlines the importance of PWV and aerosol radiative effects in the climate-sensitive Himalayan region. Furthermore, it provides a comprehensive investigation of the combined impact of aerosols and water vapour on the radiation budget.
Understanding Precipitable Water Vapour
One of the most rapidly varying components in the atmosphere, Precipitable Water Vapour is primarily accumulated in the lower troposphere. It is equivalent to the depth of liquid water obtained when all the water vapor in the atmospheric column is condensed and precipitated. PWV is used to diagnose the atmospheric humidity over a specific location.
Why are Such Studies Needed?
The large variability of PWV in space and time, mixing processes, contribution to a series of heterogeneous chemical reactions, and sparse measurement networks, especially in the Himalayan region, make it difficult to accurately quantify the climatic impact of PWV over space and time. Moreover, aerosol-cloud-precipitation interactions over this region are poorly understood due to lack of proper observational data.
Characteristics of the Himalayas
The Himalayas are the world’s highest and youngest fold mountain ranges. Bearing young, weak, and flexible geological structure, they are one of the highest earthquake-prone regions globally due to the ongoing process of Himalayan uplift. The Himalayas separate India from China (Tibet). The region provides water to a large part of the Indian subcontinent via numerous holy rivers like the Ganga and Yamuna. Interestingly, the Himalayas comprise several parallel mountain ranges extending along the North-West to the South-East direction (known as the Strike of the Himalayas), separated by longitudinal valleys. These ranges include Trans-Himalayas, Greater Himalayas or Himadri, Lesser Himalayas or Himachal, Shiwaliks or Outer Himalayas, and Eastern Hills or Purvanchal.
