National Stable Isotope Baseline for Precipitation in Malawi to Underpin Integrated Water Resources Management

Abstract

With the resurgence of water-isotope tracing applications for Integrated Water Resource Management in developing countries, establishing a stable isotopic baseline is necessary. Developing countries, including Malawi, continue to struggle with the generation of consistent and long-term isotopic datasets due to non-existent or inadequate in-country water-isotope capacity. Malawi has made significant advances in its quest to establish a stable isotopic baseline through the establishment of the Malawi Network of Isotope in Precipitation. This study provides the first results for the isotopic characterization of precipitation in Malawi with a view to reinforcing understanding of the country’s hydrological cycle. Error-in-variables regression defined a Local Meteoric Water Line as δ2H = 8.0 (±0.3) δ18O + 13.0 (±2.0) using stable isotopic records of 37 monthly samples from 5 stations between 2014 and 2019. Local precipitation (isotopic composition) is consistent with global precipitation expectations, its condensation-forming process occurring under equilibrium conditions and a higher intercept (d-excess) above the 10‰ for Global Meteoric Water Line, implying that air moisture recycling significantly influences local precipitation. Wider variations observed in local precipitation isotopic signatures are largely attributed to different moisture-bearing systems and diverse geographic factors across the country. Additional stations are recommended to improve spatial coverage that, together with longer temporal records, may help understanding and resolving uncertainties such as the altitude effect. This pioneering study is expected to facilitate Malawi’s ambition to achieve integrated use and improved protection of its surface water and groundwater resources in response to mounting climate change, growing population and land-development concerns.