This study investigated how sporadic river datasets could be used to quantify temporal variations in the base flow index (BFI). The BFI represents the baseflow component of river flow which is often used as a proxy indicator for groundwater discharge to a river. The Bua catchment in Malawi was used as a case study, whereby the smoothed minima method was applied to river flow data from six gauges (ranging from 1953 to 2009) and the Mann-Kendall (MK) statistical test was used to identify trends in BFI. The results showed that baseflow plays an important role within the catchment. Average annual BFIs > 0.74 were found for gauges in the lower reaches of the catchment, in contrast to lower BFIs < 0.54 which were found for gauges in the higher reaches. Minimal difference between annual and wet season BFI was observed, however dry season BFI was >0.94 across all gauges indicating the importance of baseflow in maintaining any dry season flows. Long term trends were identified in the annual and wet season BFI, but no evidence of a trend was found in the dry season BFI. Sustainable management of the investigated catchment should, therefore, account for the temporal variations in baseflow, with special regard to water resources allocation within the region and consideration in future scheme appraisals aimed at developing water resources. Further, this demonstration of how to work with sporadic river data to investigate baseflow serves as an important example for other catchments faced with similar challenges.

Developing countries such as Malawi require improved access to isotope tracer tools to better characterize and manage water resources threatened by land development, deforestation and climate change. This is the first published study to use an isotope facility developed in Malawi for this purpose, instead of relying upon sample analyses from abroad. Results from this new facility are used to evaluate an important Lake Malawi catchment in the Rift Valley. This work successfully established a stable-isotope baseline, hydrochemical signatures, and system conceptualization against which future policy change and management strategies may be measured. Precipitation isotopic composition was consistent with the Global Meteoric Water Line, but varied, confirming different precipitation systems nationally. Groundwater largely followed a Local Meteoric Water Line, with limited isotopic variation indicating predominant areal groundwater recharge, but with dry-season evaporative enrichment of groundwater near Lake Malawi. Surface-water isotopes widely varied with local precipitation, suggesting the latter accounted for wet-season river flows, but upstream dambo (complex wetlands occupying a shallow, seasonal waterlogged depression) helped sustain dry-season flows. Isotope capacity reinforced water-resource conceptualization and provenance in a hydrologically complex, but not atypical, Rift Valley system, exhibiting a noted complexity of groundwater–surface-water interactions. The latter, critical to integrated water resource management, requires more focused study, to which an expanded array of isotopes will contribute to tracking Sustainable Development Goal 6 targets. This study and future catchment studies should help underpin Malawian water-resource policy implementation on several identified fronts.