Saltwater intrusion into Mozambique’s Zambezi Delta: impacts on agriculture, fisheries and health

Abstract

Saltwater intrusion, intensified by climate change, threatens coastal and estuarine ecosystems and human livelihoods. This study estimated salt intrusion dynamics in the Zambezi Delta, Mozambique, focusing on impacts to surface water, groundwater, soil salinisation, agriculture, fisheries and public health. Using a predictive model for salt intrusion into estuaries and the Ghyben–Herzberg empirical relation, we applied hydrological data from 1990 and 2020, and made a projection for 2070 that incorporated a 33% river discharge reduction and 65 mm year^-1 sea-level rise. Furthermore, we applied sensitivity analyses to account for uncertainties in physical and climatic factors to make long-term projections for 2020 to 2070. Surface-water salt intrusion at the 1 ppt threshold advanced into the delta from 19.0 km in 1990 to 20.0 km in 2020, and was projected to reach 22.3 km by 2070. The groundwater salinity in all 20 sampled wells in the town of Chinde (near the mouth of the Zambezi Delta) exceeded the 0.25 ppt threshold set for potable water, with projections of up to 0.7 ppt by 2070. Semi-structured interviews with 50 farmers in Chinde in 2020, along with secondary data from local agricultural reports, indicated that soil salinisation has reduced rice yields by ∼20–40%. Preliminary catch data from Mozambique’s fisheries department suggested a shift towards marine species. Finally, health-sector data indicated that brackish-water-borne diseases (particularly Vibrio infections) pose a growing health risk. Adaptive strategies like saline-tolerant crops and water treatment will be critical to mitigate the impacts of salt intrusion into the Zambezi Delta.