Impacts of climate change on groundwater quality in Coimbatore smart city areas of Tamil Nadu, India

The impact of climate change is ubiquitous on all earth systems, including groundwater resources. The present study investigated the impact of climatic factors such as temperature and rainfall on groundwater resources in the Coimbatore smart city areas of Tamil Nadu, India, for 30 years (1990-2019). The study results revealed that the mean annual temperature (MAT) and mean minimum temperature (MMinT) in Coimbatore smart city areas had a significant annual increase in temperature by 0.24 degrees C and 0.48 degrees C per decade, respectively, which was evident during the northeast monsoon than the summer season. The region's annual total rainfall (TRF) declined by about 22 mm/decade. In contrast, the depth of the water table increased by 3 m in both the northeast monsoon and summer seasons might be due to the development of artificial recharge structures. The groundwater in the study area predominantly contained Ca-Cl (49%), Ca-HCO3 (35%), and mixed Ca-Mg-Cl (17%) might attribute due to the lower groundwater table. It was found that the groundwater quality index during the recent decade was poor. The levels of groundwater quality parameters were significantly increased over a decade during the northeast monsoon: EC, TDS, Cl-, HCO3-, total hardness, Na+, SO42-, NO3-, K+ and CO32- and summer season: EC, TDS, Cl, K+ and NO3-, respectively. An increase of 1 degrees C MMinT has increased the groundwater concentrations of EC (176 mu S/cm), TDS (105 mg/l), Cl- (43 mg/l), Na+ (24 mg/l), K+ (7 mg/l) and CO32- (- 2.7 mg/l) during northeast monsoon season; and Cl- (65 mg/l), K+ (7 mg/l), NO3- (10 mg/l) and CO32- (- 4 mg/l) during the summer season. Temperature attributed to the change in the groundwater quality parameters by 20% (TDS), 22% (EC), 31% (Na+), 30% (K+), 29% (Cl-), 33% (CO32-) in northeast monsoon and 54% (K+), 40% (Cl-), 95% (CO32-), 111% (NO3-). The impact of summer temperature is higher compared to the northeast monsoon season. Even though the impact rate of 1 degrees C MMinT on groundwater quality was numerically low, the average concentrations of NO3- and EC exceeded the permissible limit of drinking water standards, and Cl- exceeded the acceptable limit. As the trend increases, these impact rates will further increase. This trend will make groundwater unsuitable for drinking as the change in groundwater quality with respect to the temperature increases by 13-332%. Thus, sustainable groundwater management practices should be adopted. Groundwater policy should emphasise any pre-emptive actions to make groundwater resilient to thrive under uncertain future climatic scenarios.