Indiscriminate human activities around lakes deplete groundwater more than climate change impact does, says a study done by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).
Through a modelling study of the Himayat Sagar lake in Hyderabad, it showed that the extensive and haphazard cultivation of water-intensive crops in the catchment areas is leading to diminishing precious rainwater harvesting efforts through the excessive use of groundwater.
The study reported that nearly 50 per cent of the water harvested by hydrological structures helped increase groundwater recharge. However, crop area expansion using groundwater for irrigation 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, ICRISAT Development Centre (IDC).
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.
They also 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 (rainfall and temperature) in the future.
“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, IDC.
Researchers at the IDC studied historical data on climate, land use, watershed structures and groundwater levels available with the Telangana government organizations 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 analysed 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.
The ICRISAT 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.
Under the ‘Mission Kakatiya Program,’ village tanks were desilted, rejuvenated and interlinked with the drainage network. According to model predictions, this mitigation strategy captures excess runoff, enhances groundwater recharge for upstream users and helps control flood damage to downstream users during high-intensity rainfall events.
“It is also necessary to have a better water resource governing policy for the administration of village tanks, especially during the dry years, for the benefit of downstream users,” said Dr Rajesh Nune.
ICRISAT’s modelling has been designed to inform better public policy leading to improved natural resource management and enhanced farming productivity.
“The analytical framework employed will help policymakers 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 Nune.