Human activity around lakes depletes groundwater more than climate change: ICRISAT study

Hyderabad: Indiscriminate cultivation of water-intensive crops in the catchment area of Himayat Sagar is diminishing precious rainwater harvesting efforts through excessive use of groundwater, anICRISAT modeling study has revealed.

The findings point to a need for improved governance of water resource sustainability which remains a critical challenge, particularly in semi-arid regions where despite an increase or no change in rainfall, there is a steady decline in the stream flow of catchments.

"We observed that nearly 50 per cent of the water harvested by hydrological structures helps to increase groundwater recharge. However, crop area expansion using groundwater for irrigation has depleted stream flow and groundwater storage in the Himayat Sagar catchment. The annual groundwater recharge in the catchment is able to fully meet the irrigation requirement during high rainfall years, 50 per cent during dry years and 30 per cent during normal years," said Dr Rajesh Nune, Hydrologist at ICRISAT Development Center (IDC).

Researchers at the IDC studied historical data on climate, land use, watershed structures, and groundwater levels available with the Telangana government organisations and conducted field surveys to gather data on groundwater utilization for different cropping systems during the rainy (Kharif) and post- rainy (Rabi) seasons.

The data was analyzed using an integrated hydrological model called 'Modified Soil and Water Assessment Tool (SWAT).' The approach combines SWAT's rainfall-runoff model with a groundwater model for each of the 19 sub-catchments in Himayat Sagar. The model is structured to capture dynamic changes in climate variability, land use, and watershed development structures in the catchment.

Adaptation to climate variability in the future

The ICRISAT-led study also explored the future impact of potential climate and catchment changes on stream flow and groundwater storage in the Himayat Sagar catchment. The model explored factors such as expanding groundwater irrigated areas, watershed structures, and rejuvenation of existing tanks under the Telangana Government's 'Mission Kakatiya' in the future. Notably, the State is expected to witness the highest rainfall in September instead of August by the end of this century in light of rising temperatures and climate change.

ICRISAT's findings reveal that despite the increase in average rainfall, a decline in stream flow is expected, considering variations in seasonal rainfall in the months of May and November. Critically, the study observed that catchment changes would have a more significant impact than climate change in the future.

Efficient planning of cropping systems based on available resources ICRISAT's modeling has been designed to inform better public policy leading to improved natural resource management and enhanced farming productivity.

"The analytical framework ICRISAT has employed will help policymakers to take appropriate measures to monitor the cultivation of water-intensive crops (paddy, sugarcane, maize, etc.) and guide farmers to diversify their crops while ensuring efficient use of water resources in their region," said Dr Rajesh Nune.

"Understanding the impact of climate variability on stream flow and groundwater recharge along with land use change will help water resource managers adopt better landscape management practices in the catchments for current and future water requirements," concluded Dr Sreenath Dixit, Head of IDC.