Is there any trend in groundwater level in South India? Case study from Telangana State, India.

Worldwide groundwater is under an increasing pressure, mainly for agricultural water uses. Among that, India is the first groundwater user. Indian agriculture has exceeded the total available groundwater resources, which in turn have put a serious concern on food security as well as aquifer health.  Therefore, trend indicator is commonly used in analysis of groundwater level time series, showing clear drop of water level in North west of India. Nevertheless, the trend analysis in South India does not appear obvious. This work intends to raise awareness about the strength but also the weakness of time series trend analysis of groundwater level. This work uses the Telangana state in south India as a case study. Indeed, the Central Groundwater Board, used one of the most dense piezometer system in the world to estimate the ratio of groundwater extraction to aquifer recharge. The state average is 65 % (Excluding Hyderabad, the main city, where it is 340 %). Over the last 20 years, the state groundwater level shows a gentle declining trend of 0.8 m per year. However, this trend hides local and temporal disparities that cannot be neglected.

Mann–Kendall and Sen’s slope tests were accomplished on monthly groundwater level data from 2007 to 2020 over more than 1000 monitoring borewells to investigate the annual and seasonal groundwater-level trends. The trend information was mapped at Telangana state scale (110 000 km2) and estimated for different periods depending on climate conditions (very rainy year or at the opposite in drought condition). These results allow us to identify the impact of irrigation practices changes considering the hydrogeological setting and the resilient behaviour of users.  Indeed, the spatial distribution and time period chosen can have a tremendous impact on the conclusion of trend analysis in South India. 

On a first hand, this work proposes to highlight the main misunderstanding that trend analysis could bring in this kind of groundwater system, and on another hand, to show the enhancement of knowledge that this technic allows. The trend analysis need to be adapted to the local context to raise alert and help the decision makers to improve groundwater management.