[PULA Project] Extreme rainfall and floods in arid regions: replenishment or contamination of water resources?

While recent research suggests that recharge of groundwater resources in arid regions, including Sub-Saharan Africa, only occurs during extreme rainfall events, these conditions are also associated with the mobilisation of contaminants into surface water and aquifers. Scarcity of clean surface water has already put tremendous pressures on water resources in arid developing countries. Projections of growing populations and more pronounced climatic extremes suggest that sustainable approaches to water resources are urgently needed, but there are key deficiencies in understanding of 1/the mechanisms and timing by which water stores (surface and ground) recharge and get contaminated as a result of heavy rainfall and 2/the associated trade-off between increasing water storage but also potentially of poorer water quality.

The current exceptional ongoing rainy season in Botswana provides an urgent opportunity to study the effects of heavy rainfall on water resources in arid countries. The last heavy rainfall occurred nearly two decades ago and the exceptionally wet conditions have activated potential migratory routes for leachate from dumpsites to ground and surface water. Such point source pollution provides ideal opportunistic conditions for large-scale tracing of flow and contaminant pathways in arid environments.

The proposed work aims to take advantage of this unique prospect to monitor the immediate effect of heavy rainfall and floods on water resources and their transitional hydrologic readjustment towards the dry period, and elucidate whether these events support either or both resources replenishment and contamination. The densely populated Gaborone reservoir catchment is of particular interest because water demand and pollution sources are high and preferential flow pathways in the fractured bedrock result in fast groundwater recharge and contamination. Erosion of shallow soils affects sediment and contaminant transport, as well as geomorphological conditions which in turn impact on recharge patterns.

We will utilise the unique opportunity to evaluate the crucial link between water quantity and quality, often investigated separately, through an integrated approach that combines hydrologic monitoring, temporal geophysical imaging, geomorphological mapping and natural tracer experiments (leachate and stable water isotopes) with modelling. Experiments will span the ongoing wet season and its transition to the following dry season. Water monitoring and sampling will focus on existing ground and surface water points across the catchment as well as dams and potential pollution sources at different spatial and temporal scales. Integrating the datasets into the modelling framework will allow for characterising and quantifying the contribution of extreme rainfall events to water resources replenishment and contamination.

The project team is composed of UK and African scientists with specialisations in hydrogeology, surface water hydrology, geophysics and sedimentology and water governance stakeholders. Research will benefit from a hydrometric monitoring in place and in-kind sample collection pre-award, which will be expended during the project.

The overall research outcomes will be 1/a greater understanding of the key processes governing flood-induced water resources replenishment and contamination in arid developing regions and 2/an increased ability of water resources stakeholders to adapt management and policy to the foreseeable increase in hydrological extreme events.

The new science generated will impact both the academic community interested in new methods and knowledge with regards to hydrological processes under changes, and the governance sector in arid (sub-Saharan) regions in need of adaptive water management strategies able to cope with both short and long term effects of climate change. Students and project partners will receive training and early career researchers will build their research portfolio.

This project will have various academic and socio-economic impacts on four groups of beneficiaries:

1.Inhabitants of Botswana and African arid regions: A significant proportion of the population of Botswana, and of the wider arid part of sub-Saharan Africa is dependent on vulnerable water resources in low-storage fractured basement rocks that are exposed to increased frequency of extreme rainfall events. On the short term, the project will impact the local people through enhanced awareness of the issues surrounding water resources from direct interactions in the field and from participation of representatives of local community water associations to the project stakeholder workshop. On the mid to long-term, the outcome of the research will have wider impact on people from arid regions by contributing to increased knowledge of climate impact on water resource therefore a more sustainable provision of safe water, hence improving their well-being.

2.Local and regional authorities (governance): The project will contribute to improve water governance and policy through provision of evidence-base for (i) revision/upgrade of the DWA groundwater monitoring network from identification of catchment areas most sensitive to flood-induced recharge and contamination; (ii) proposition/prioritization for reclaim of major contaminated sites; (iii) development of a specific system for monitoring anthropogenic contamination around point source pollution risk areas. The new knowledge on the timescale of response of water resources to extreme rainfall and floods will be useful to the decision-makers and environmental manager to adapt their response/mitigation capacity to hydrological disasters. The impact on the Botswana water governance sector will be achieved through (i) early involvement of the Department of Water Affair (DWA, project partner) in the design of the field surveys and sampling routines as well as selection and instrumentation of new relevant water monitoring points and (ii) participation national and regional representatives of DWA to the final workshop delivered.

3.General public in the UK, Africa and beyond: We aim to raise public awareness on how important and fragile the water resources are in arid regions and how they are related to climate variability and extremes. Throughout the project we will work with the Public Engagement with Research Unit at UoA, which coordinate and deliver a range of public facing events. We plan to hold an event at the 2018 British Science week, which takes place annually in March. In particular, we will target both adults and children, with presentations based on photos and videos acquired during the fieldwork. In addition, a webpage will be created on the University of Aberdeen's website with information and news updates and we will approach UK and Botswana media for coverage of major discoveries.

4.Academic communities: The international academic community will learn from the findings that will provide light on key processes that determine water sustainability in developing arid countries subject to increasing frequency and magnitude of climate extremes. The impact will be achieved through an international conference presentation, open-access, high-impact journal publications, and storage of the project data in the RCUK Data Centres. Our Partner IMWI will provide synergies with parallel ongoing water research initiatives in Botswana and Southern Africa that they are leading, which will contribute to increase the regional impact beyond the strict project team and studied area. In addition, the research will contribute to train and inspire five students (BSc and MSc) from the partner BIUST, who will be involved in all fieldwork activities and data analysis, and will complete their dissertations/thesis as part of the project. The early career researchers through coordination of workpackages and tasks will develop their leadership skills and portfolio, hence their career development.