Manoj Mishra
A Delhiite landing in Port Blair (A&N Islands) could feel kind of lost in the head for a few hours or even days before acclimatization sets in. This is not due to jet lag but the invisible water in the air, actually lots of it. Hot and humid as they say could be killing for somebody not used to it and global warming is making it worse.
Humidity is nothing but water in the air that you don’t see but can feel. And since most things out of sight are also often out of mind so is moist air. But water vapour in the air is not the only water that is lesser-known or appreciated. Let me explain.
Water Cycle
Water in warming sea evaporates to become clouds. Wind led clouds to travel far and precipitate as rain and snow both on earth and on the sea itself. On earth, some of it runs off into streams and rivers and end up back in the sea. Some percolate down into the earth to become groundwater and some evaporate back into the atmosphere.
The water that percolates into the ground remains invisible till it emerges as a spring on a hill slope or is pumped up a well. There is yet another form of poorly appreciated water called ‘soil moisture’.
Some of the rain and snow as it percolates into the ground is retained by the soil between its particles. Water retained in the upper 10 cm of soil is termed surface soil moisture and up to 200 cm depth is called root zone soil moisture which is readily available to plants. This along with dew is the secret of rain-fed agriculture and all the vegetation that grows by itself without the involvement of any human agency.
Water on Earth
According to a 1993 estimate by Igor A. Shiklomanov, most water on earth which is some 96.6% is in the seas. Then at 1.76% comes water in ‘solid state’ as Icecaps, Glaciers, Permanent Snow, Ground Ice and Permafrost. ‘Groundwater’, both fresh and saline are next at 1.69%. ‘Lakes’, both fresh and saline water constitute .013% while ‘Soil moisture’ and ‘Atmospheric water’ tie at .001% each. ‘Rivers’ at .0002% trail way down the list.
A more recent NASA report of 2015 says that of all precipitation that falls over the land on earth, some 60% returns back as water vapour to the atmosphere. This means that it is the remaining 40% that together accounts for water that flows in rivers, percolate to become groundwater or stand as soil moisture. Another interesting fact is that 98% of Earth’s ‘available’ freshwater is groundwater. It is about 60 times as plentiful as the freshwater found in lakes and streams.
While most people think that water is largely that stands in lakes, flow in rivers or is brought up from wells for this is what they either see or use, they realise little that at any point of time there is more water in the atmosphere as water vapour/clouds or is sitting as soil moisture than all the water flowing in the rivers.
Water Budget
The water budget describes the water cycle. How much water has precipitated over a year, how much of it has returned to the atmosphere, how much is locked as soil moisture or infiltrated to become groundwater and how much is returning back to the seas via the rivers?
Researchers are finding that with global warming earth’s water budget is going to witness drastic changes with profound implications both for water and food security on earth.
While warming oceans would evaporate more water into the atmosphere, warming lands would desiccate the soils, increase evapotranspiration as well as rapid water loss to evaporation from lakes, reservoirs, rivers and possibly even from shallow aquifers. Earth is slowly but surely becoming overloaded with moist air.
Implications of Humid Earth
It has been estimated that with every degree centigrade rise in global temperature, the air increases by 7% its capacity to hold more water. That means greater humid conditions, more clouds in the sky and greater precipitation (rain, snow etc).
But it also means greater global warming since water itself is a greenhouse gas. The reason why we feel warm on a ‘cloudy’ winter day compared to a cloudless one. Interestingly water in the atmosphere is a coolant too on account of its albedo (clouds reflecting back into the atmosphere the heat of sunrays) effect. The key difference between Water and CO2, methane etc as greenhouse gases is that the latter are not condensable as water is and hence their accumulation is deadly. No wonder climate researchers are having a field day with water as the most intriguing variable in the equation.
More floods and drought conditions, sharp loss of soil moisture content and even water from shallow aquifers to evaporation, non-seasonal rains and lack of rain when it matters most is likely to play havoc with food and water security on earth.
This change from the ‘normal’ dry and wet climatic conditions are also bewildering ‘Plants’ (trees, shrubs, herbs, lianas, grasses, ferns etc), ‘Fungi’ as well as non-human ‘Animals’ (mammals, birds, fish, reptiles, insects etc) on lands and in wetlands including the oceans. Alas, for many of them extinction might be in-store due to their inability to adapt adequately and timely to the changing environment.
Monsoon
The greatest area of concern for us in India is the manner in which global warming is going to affect the Monsoon system. This is because the monsoon is the bulwark on which the ecology and economy of India rest.
A recent German study from April 2021 on the impact of global warming on monsoon in India concluded after using 30 different climate models that “for every degree Celsius rise in global temperature monsoon rainfalls will likely increase by 5%”.
While this statement may not by itself convey much other than an increase in rainfall, it is the lived experiences of people in the Kumaon region of Uttarakhand and those in Kerala from October 2021 – when unprecedented high-intensity rainfall during a month when monsoon should ideally have gone to sleep brought widespread devastation and loss of life and property – that tells the real meaning of the increase that the researchers are talking about.
If more confirmation is needed then talk to the farmers who had still to shift the harvested paddy from their fields when the ‘unwanted’ rains came or to the family members of the trekkers who never returned from the high altitude treks they went on during otherwise a safe month.
Global warming is making monsoons behave strange, to say the least. If it is super wet over a week or two, it is menacingly dry the next few weeks, keeping almost everybody from farmer to economists to weathermen to birds guessing. The nation’s water lifeline has been compelled by forces beyond its control to behave erratically.
In short future on the monsoon front looks baffling.
Heated Surfaces
Global warming heats all exposed surfaces. Be it land or water.
This means accelerated evaporation of water from lakes, reservoirs and soils. And if a drought year comes along then the situation can go from bad to worse. As it is thanks to rising ambient temperatures the Himalayan glaciers lost billions of tons of ice between 2000 and 2016. This was double the loss reported between 1975 and 2000.
National Water Budget
With the situation developing as above it is time that we as a nation took an informed stock of our national water budget with climate change adaptation in mind.
A 2011 figure at Water Resources Information System (WRIS) maintained by the Central Water Commission (CWC) reports for India a total of 4,000 cubic km as annual precipitation (including snowfall). Of this 53.3% is estimated to be the sum total of water that returns to the atmosphere as water vapour plus the soil water. While 46.7% is the potential surface flow in the rivers.
Surprisingly the above estimate does not account for the portion of annual precipitation that infiltrates into the ground to reside as unconfined and confined groundwater unless it has been subsumed into the term ‘soil water’?
But if the latter is true then it is unacceptable because soil water/moisture as discussed before is limited to no deeper than 200 cm. Presumably, there is a problem with the manner in which the CWC has budgeted water at a national scale.
The call for CWC to reassess India’s water budget has been a standing concern amongst academicians and water activists best exemplified by a 2008 paper by Prof. T.N. Narasimhan with a focus on the underestimation of losses to evaporation. In his words ‘there is sufficient evidence to suggest that the budget estimates may be seriously overestimating available and utilizable water resources in the country.
While the jury is out on the correctness of the national water budget the scourge of global warming has already caught up with us and we cannot afford to wait anymore before revisiting the water budget in a transparent and participatory manner. Lest, as a nation, we are caught napping when a serious water scarcity thanks to global warming hit us. God Forbid!
First Published in The Dialogue Climate Change: Let’s Talk Specifics, How About Water Budget? on November 2, 2021.
About the Author
Manoj Misra, Convener, Yamuna Jiye Abhiyaan.
