Seasonal dynamics of submarine groundwater discharge zones along the Southeastern Arabian Sea coastline.

The study aimed to identify and monitor potential submarine groundwater discharge (SGD) zones by integrating thermal infrared (TIR) remote sensing with groundwater dynamics, particularly groundwater level and electrical conductivity along the Southeastern Arabian Sea (SeAS) coastline. Sea surface temperature anomalies were detected in pre- and post-monsoon seasons using TIR imagery to identify SGD sites along a ~ 600-km stretch of SeAS. Coastal rivers and streams were delineated to identify sea surface temperature anomalies from surface runoff. Groundwater level and electrical conductivity of coastal aquifers were analyzed from 2017 to 2022 to characterize potential SGD zones. The results show varying cold-water anomalies linked to SGD of colder groundwater into the ocean, with notably higher anomalies post-monsoon due to increased groundwater recharge from monsoonal rainfall. Some anomalies are linked to direct surface water discharge from coastal rivers/streams. Groundwater level analysis shows that about 240 km of coastline shows groundwater levels reaching up to 50 m above mean sea level (msl) seasonally, leading to significant SGD during pre- and post-monsoon periods. Some areas with low groundwater levels in both seasons experience seawater intrusion, putting about 250 km of coastline at risk of SGD extinction due to groundwater levels near msl. The electrical conductivity of groundwater shows that 86.4% of the coastline has fresh SGD, while 12.9% and 0.6% have brackish and saline SGD zones, respectively. Overall, the study reveals spatiotemporal variation in SGD along the SeAS, with findings useful for coastal groundwater management and ecosystem protection.