Down To Earth|May 16, 2020
Nature-based solutions like planting of trees and restoration of forests are often touted as the panacea for water conservation. This is because forested watersheds—lands covered by forests which drain all the water flowing through them into waterbodies like rivers or lakes—provide a whopping 75 per cent of the world’s accessible freshwater resources. But many organisations implementing this crucial nature-based solution have been unable to differentiate between restoration of forests and planting trees.
For instance, in India, afforestation was one of the interventions of the Union government’s Jal Shakti Abhiyan, launched in July 2019, to make the country’s most water-stressed districts water secure. Under this programme, district administrations were encouraged to undertake planting of trees in a big way. The enthusiastic local authorities reported a staggering number of afforestation activities which turned out to be fudged data, as admitted by district officials as well as a senior official in the Jal Shakti ministry. Even if these numbers were real, simply planting trees will not conserve water. In fact, trees can suck up water and release it through evapotranspiration—water lost by trees to the atmosphere through tiny openings on the underside of their leaves known as stomata.
“Studies conducted in various parts of the globe, especially in semi-arid and arid regions have shown that blind afforestation does not increase water supply,” says Gopal Singh Rawat, former dean of the Wildlife Institute of India, Dehradun. “When sparsely vegetated land is converted into forest, there is a reduction in blue water (available for human use) and increase in green water (part of water available for plant use). Trees can consume more water than other shorter vegetation. According to the mass balance principle, if more water is used by trees, less water will flow into rivers and lakes or recharge the groundwater that people can directly use,” he says.
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May 16, 2020