Trend Identification in Groundwater Levels and Exploring Linkages with Rainfall and Irrigated Areas in Arid Region of Rajasthan, India

Aquifers underlying the arid lands of Rajasthan are under stress due to expansion in groundwater-irrigated areas. This study investigated trends in the long-term groundwater level and explored linkages of groundwater with rainfall and irrigated area in 12 districts of the arid region of Rajasthan, India using 64-year (1957-2020) rainfall data of 62 stations and 36-year (1984-2019) groundwater-level data of 4042 sites for pre-monsoon and post-monsoon seasons. Box-whisker plots of the district-wise average annual rainfalls were drawn. Trends in groundwater levels were identified by employing Mann-Kendall test and their magnitudes were quantified using Sen’s slope estimator test. Furthermore, linkages of groundwater levels with rainfall and groundwater-irrigated areas were evaluated through correlation and linear regression analysis. Results indicated that annual rainfall increased at a rate of 18 mm year^-1 over the last 2 decades. Also, annual rainfall crossed an amount of 400 mm in 7 of recent 10 years. The declining trends (p<0.05) of groundwater levels were identified at more than 50% sites mainly located in Jalor, Jhunjhunu, Pali, Sikar, Nagaur and Jodhpur districts. In contrast, rising trends in Sriganganagar, Hanumangarh and Bikaner districts were attributed to excessive canal-irrigation and poor-quality groundwater. Declining groundwater levels were more prominent in Jalor, Jhunjhunu, Nagaur and Sikar districts in post-monsoon (>0.60 m year^-1) as compared to pre-monsoon (0.40-0.50 m year^-1) season. Groundwater levels revealed poor response to rainfall as evidenced from weak linear relationship with low correlation coefficients (r) values. On the contrary, groundwater-level revealed moderate to strong linkages with irrigated areas based on r ranging from 0.58 to 0.94 and 0.68 to 0.96 during pre-monsoon and post-monsoon season, respectively. Findings of this study suggest need for adopting good strategies like harvesting surplus rain/runoff water and utilizing the harvested water judiciously for irrigation or groundwater recharge. However, this will require developing incentive-based policies to encourage farmers and other stakeholders to adopt water harvesting and help curtail excessive groundwater extraction for irrigation. In addition, reducing subsidies on electricity and promoting less water-requiring crops and adoption of water-saving technologies can be part of the policy framework.