Understanding the impact of climate-induced sea level rise on groundwater inundation in a low-lying coastal area: A numerical simulation in Southeast India

Abstract

Global warming has led to rising sea levels, severely threatening coastal areas, particularly in low-elevation coastal zones. The groundwater in coastal aquifers of lower elevation is susceptible to groundwater inundation (GWI), an emerging hidden long-term hazard earlier to marine inundation. The inundation is mainly due to the hydraulic connection between sea level and shallow unconfined aquifers, resulting in groundwater upsurging towards the ground surface. To understand the potential impact of sea level rise (SLR) induced GWI on low-lying coasts, a transient state model was simulated and predicted in the Cuddalore regions of South India under 0.3 m, 0.6 m, and 1 m SLR scenarios. The simulation reveals that the aerial extent of groundwater rise (GWR) was 331.9 km2, 566.2 km2, and 650.8 km2 for 0.3 m, 0.6 m, and 1 m SLR scenarios, respectively. About 50% of the response was observed in the northern and central parts of the study area within a 5 km buffer, which is attributed to the deeper groundwater table. In contrast, the southern region exhibited a 10% decline in response due to shallow groundwater discharge to drainage, which dampened the shoaling effect. The present-day shallow groundwater tables in the southern region are more vulnerable to GWI from rising sea levels. Specifically, a 0.3 m SLR could inundate 14.9 km2. In comparison, a 1 m SLR could inundate 40.5 km2 of the area, including the Pichavaram mangrove forest, agricultural land, municipal structures, and the other regions that flooding could threaten. These inundations could have potential impacts, such as wetland loss, agricultural flooding, deteriorating water quality, and infrastructural damage. The present study provides valuable insights into the subsurface hydrodynamic and exposure impacts of sea rise-induced inundations. This can aid coastal engineers, policymakers, and decision-makers to plan appropriate mitigation measures.