Sinking delta: Quantifying the impacts of saltwater intrusion in the Indus Delta of Pakistan

Abstract

This study focused on an integrated assessment of coastline change and its impacts on the deltaic sustainability of the Indus Delta, the world's fifth-largest delta. The increase in salinity and degradation of mangrove habitat was examined using multi-temporal Landsat satellite imagery from 1990 to 2020. The tasselled cap transformation indices, multi-statistical End Point Rate and Linear Regression were used to extract the shorelines rates. Mangrove cover area was estimated by applying the Random Forest clasification approach. Impacts of coastal erosion on mangroves and sea-water salinity were determined through the association between electrical conductivity and vegetation soil salinity index (VSSI). The accuracy of the analysis was evaluated using ground truth information obtained from field surveys and Fixed-Point Photography. Major findings of the analysis indicate that the North-West Karachi experienced accretion at an average rate of 7.28 ± 1.15 m/year, with medium salinity (VSSI<0.81) and increased mangrove cover, from 11.0 km2 area in 1990 to 14.5 km2 in 2020. However, the Western Delta has undergone massive erosion at a mean rate of −10.09 ± 1.61 m/year with obtrusive salinity (0.7 ≤ VSSI ≤ 1.2) and 70 km2 of mangrove cover loss. In the Middle West Delta and Middle East Delta erosion is observed at an average rate of −28.45 ± 0.55 m/year rate, with high obtrusive salinity (0.43 ≤ VSSI ≥ 1.32) and rapid mangroves cover loss (14 km2). The Eastern Delta was relatively stable and accelerating towards the sea with increasing mangrove cover (629 km2). Our analysis revealed that erosion, which occured due to reduced sediments flow linked to development of water infrastructures as well as climate change, have serious implications for the ecosystem. Future policy and action-plans should priotitise addressing vulnerabilities by integrate nature-based solutions for revival of the Delta.