Abstract
Traditional tanks in arid regions of India have been working to address water demands of the public for more than 2000 years. However, recent decade is witnessing growing domestic and agricultural water demand coupled with rising encroachment and ignorance toward tanks; consequently, intensifying water shortage issues. While climate change is impacting at alarming rates, local agencies have forgotten these tanks that have aided in sustainable water supply solutions for decades apart from municipal water supply. This research, for the first time, estimates water supply-demand for an arid region in South India (Madurai) and lists out the benefits if tanks were managed and desilted. Exploratory investigations for documenting seasonal domestic and agricultural unmet water demand were conducted followed by their validation through ground-truthing across the study period 2002–2019. Results indicated high unmet domestic water demand, estimating ~73% [maximum 365 thousand cubic meters (TCM)] for summer (March to May) and ~33% (maximum 149 TCM) for winter (January and February), and high unmet agricultural water demand estimating ~90% (maximum 5,424 TCM) during North-East monsoon (October to December), and ~95% (maximum 5,161 TCM) during South-West monsoon (June to September). Erratic rainfall pattern was identified as a major cause for higher fluctuations in water availability inside tanks ranging 0–50%, while lack of ownership resulted in increased siltation load ranging 30–70% of the tank's volume. The study found that the major portion of the unmet water demand can be accounted for through rehabilitation of the tanks, as under the rehabilitated tank irrigation scenario the tank storage could attain 200–400% more water than the estimated agricultural water demand. It was concluded that if the cascade tanks were managed appropriately, they could have positive impacts by reducing floods and providing water for drought seasons.
Highlights
In order to meet the targets of Sustainable Development Goal 6 (SDG 6), it is essential to overcome the challenges for attaining surface and groundwater security and sustaining adequate water supply, especially in the countries that are under-developed or developing (Chinnasamy and Prathapar, 2016; Benson et al, 2020; Chinnasamy et al, 2021)
The tank cascade system is integral to agricultural livelihood in rural areas and mostly groundwater percolation sources in urban areas
Though the usage of tanks differed from region to region, they were commonly observed serving for drinking, protective irrigation, and natural hazard mitigation purposes
Summary
In order to meet the targets of Sustainable Development Goal 6 (SDG 6), it is essential to overcome the challenges for attaining surface and groundwater security and sustaining adequate water supply, especially in the countries that are under-developed or developing (Chinnasamy and Prathapar, 2016; Benson et al, 2020; Chinnasamy et al, 2021). Besides enabling water security provisions by considering the water demand-supply factors, the climate is yet another crucial factor impacting the water balance, thereby water supply potential of the watershed or catchment (Mehran et al, 2017; Erfani et al, 2018) Hydrological phenomena such as evaporation and evapotranspiration undergo drastic changes as a result of the rise in temperature mostly attributed to global warming. Studies have predicted that by 2050, the global population might attain a magnitude of 10 billion (United Nations, 2005) and that the GDP will increase 4fold as compared to the ongoing decade (OECD, 2012) This demographic explosion will increase the food demand by 70% which will markedly increase the agricultural water demand by several folds (FAO, 2009). Attempts to formulating water supply-demand schemes with existing water infrastructures require further attention toward improvisation in meeting unmet (deficit) water demand considering sustainability, efficiency, and security in supply facets
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