Significant drop in volume of water in Ganga, flags WMO
The volume of water available in the Ganga and the groundwater in the river-basin have both seen a significant fall between 2002 and 2021, a report by the World Meteorological Organisation (WMO) released on Tuesday said.
Titled “State of Global Water Resources 2021”, the report has identified several other global hot spots that show the same trend (of negative terrestrial water storage as WMO describes it), including the São Francisco River basin, in Patagonia, the Indus headwaters, and basins in southwestern US. In contrast, the Great Lakes region, has seen a positive trend, as have the Niger basin, and the North Amazon basin.
Overall, the negative trends are stronger than the positive ones globally, the report said. Terrestrial water storage or TWS, which includes surface soil moisture, root zone soil moisture, groundwater, snow, ice, water stored in the vegetation, river and lake water according to Science Direct, was below normal (and in some areas, much below normal) in the west coast of the US, Patagonia, North Africa and Madagascar, Central and West Asia , the central part of South America, Pakistan and northern India. TWS was much above normal in the central part of Africa, the northern part of South America, specifically the Amazon basin, and the northern part of China.
“It should be noted that at least some of the strong anomalies (Alaska, Patagonia, Himalayas, and Baffin Island) are also the result of long-term trends caused by the melting of snow and ice. Some of the hot spots of negative trends are mainly induced by over-abstraction of groundwater for irrigation,” the report explained. Overall, the report shows large areas recorded drier than normal conditions in 2021 as rainfall patterns were influenced by climate change and a La Niña event. Last year was ranked between the fifth and seventh warmest year on record (not concluded yet) with the global annual mean temperature of 1.11 ± 0.13 degree C above the 1850–1900 preindustrial average, despite prevailing La Niña conditions.
La Niña refers to the largescale cooling of the ocean surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, namely winds, pressure and rainfall. It usually has the opposite impacts on weather and climate as El Niño, which is the warm phase of the so-called El Niño Southern Oscillation (ENSO).
ENSO has a major influence on weather and climate patterns such as heavy rains, floods and drought. In India for example, El Nino is associated with drought or weak monsoon while La Nina is associated with strong monsoon and above average rains and colder winters.
The report underlined that the impacts of climate crisis on the cryosphere is critical to document the impact on water resources globally.
“The impact of glacial melt and retreat is likely to be more in the Indus basin than the Ganga basin. But the northern parts of Ganga particularly in Uttarakhand can be influenced quite a bit by glacial retreat. Downstream, there is massive extraction of groundwater for irrigation particularly Punjab, Western parts of UP etc. We know for sure that our groundwater resources are depleting. We need effective policies now because rainfall may increase due to global warming but runoff is more, so is evaporation due to high temperatures,” said M Rajeevan, climate scientist and former secretary, ministry of earth sciences.