Groundwater modelling assessment of a coastal agriculture climate change adaptation strategy incorporating green infrastructure: An Indus Delta case study

In many parts of the world, agricultural productivity is being undermined by soil salinisation. For the semi-arid to arid coastal areas of the Indus Basin in Sindh, Pakistan, salt transport into the crop root zones is enhanced by high evapotranspiration rates and the prevalence of shallow watertables. Surface water supply at this downstream end of the basin is insufficient to flush out salt build-up and the use of groundwater of marginal quality contributes to salinity accumulation. Seawater intrusion is further exacerbating these salinisation trends. To improve understanding of how these inter-related trends are impacting groundwater, we developed a MODFLOW 2005 model for a case study area in Sindh encompassing the Pinyari Canal Command Area (CCA) and coastal district of Sujawal. The SSP2-4.5 and SSP5-8.5 climate change scenarios were simulated to understand possible future outcomes from rising sea levels and reduced canal water supplies and their consequential impacts up to 2100. We then simulated a mix of adaptation strategies, including transforming cropping systems towards water efficient crops, and use of green infrastructure as a nature-based solution to build resilience by mitigating impacts from climate change along the coastal belt. However, even with these adaptations, our assessment suggested that waterlogging and salinity will only be marginally reduced, while salinity mobilisation under climate change will accelerate. The looming threats from climate change will thus require water and land managers to bolster green infrastructure with other mitigation strategies that rely on grey infrastructure, and to modify how they implement this mix of adaptation and mitigation strategies to ensure they are co-developed with coastal communities affected. Such a co-development approach is needed to ensure communities who continue to live in such semi-arid to arid coastal areas are engaged in ways that build their resilience and ongoing livelihood sustainability.