Agricultural management impacts on groundwater: simulations of existing and alternative management options in Peninsular India.

Understanding the principal causes and possible solutions for groundwater depletion in India is important for its water security, especially as it relates to agriculture. A study was conducted in an agricultural watershed in Andhra Pradesh, India to assess the impacts on groundwater of current and alternative agricultural management. Hydrological simulations were used as follows: (1) to evaluate the recharge benefits of water-harvesting tillage through a modified Soil and Water Assessment Tool (SWAT) model and (2) to predict the groundwater response to changing extent and irrigation management of rice growing areas. The Green-Ampt infiltration routine was modified in SWAT was modified to represent water-harvesting tillage using maximum depression storage parameter. Water-harvesting tillage in rainfed croplands was shown to increase basin-scale groundwater recharge by 3% and decrease run-off by 43% compared with existing conventional tillage. The groundwater balance (recharge minus irrigation withdrawals), negative 11 mm/year under existing management changed to positive (18-45 mm/year) when rice growing areas or irrigation depths were reduced. Groundwater balance was sensitive to changes in rice cropland management, meaning even small changes in rice cropland management had large impacts on groundwater availability. The modified SWAT was capable of representing tillage management of varying maximum depression storage, and tillage for water-harvesting was shown to be a potentially important strategy for producers to enhance infiltration and groundwater recharge, especially in semi-arid regions where rainfall may be becoming increasingly variable. This enhanced SWAT could be used to evaluate the landscape-scale impacts of alternative tillage management in other regions that are working to develop strategies for reducing groundwater depletion. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]