Assessing impacts of agricultural water interventions in the Kothapally watershed, Southern India

The impacts of various soil and water management interventions in the watershed are compared to no-intervention during a 30-year simulation period by application of the calibrated and validated ARCSWAT 2005 (Version 2.1.4a) modelling tool.

Kothapally receives, on average, 800 mm rainfall in the monsoon period; 72% of total rainfall is converted as evaporation and transpiration (ET), 20% is stored by groundwater aquifer, and 8% exported as outflow from the watershed boundary in current water interventions. ET, groundwater recharge and outflow under no-intervention conditions are found to be 64, 9, and 19%, respectively.

Check dams helped in storing water for groundwater recharge, which can be used for irrigation, as well minimising soil loss. In situ water management practices improved the infiltration capacity and water holding capacity of the soil, which resulted in increased water availability by 10–30% and better crop yields compared to no-intervention. Water outflows from the developed watershed were more than halved compared to no-intervention, indicating potentially large negative downstream impacts if these systems were to be implemented on a larger scale. On the other hand, in the watershed development program, sediment loads to the streams were less than one-tenth.

It can be concluded that the hydrological impacts of large-scale implementation of agricultural water interventions are significant. They result in improved rain-fed agriculture and improved productivity and livelihood of farmers in upland areas while also addressing the issues of poverty, equity, and gender in watersheds. However, there is a need for case-specific studies of such hydrological impacts along with other impacts in terms of equity, gender, sustainability, and development at the mesoscale.

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