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

虽然最近的研究表明，包括撒哈拉以南非洲地区在内的干旱地区的地下水资源补给只发生在极端降雨事件期间，但这些情况也与污染物进入地表水和含水层有关。清洁地表水的匮乏已经给干旱发展中国家的水资源带来了巨大压力。对人口增长和更为明显的气候极端情况的预测表明，迫切需要对水资源采取可持续的办法，但在了解暴雨导致储水量(地表和地面)补给和受到污染的机制和时间方面存在关键不足，以及储水量增加和水质可能变差之间的相关权衡。博茨瓦纳目前正在进行的异常雨季为研究暴雨对干旱国家水资源的影响提供了一个紧迫的机会。上一次暴雨发生在近20年前，异常潮湿的条件激活了渗滤液从垃圾场向地下水和地表水的潜在迁移路线。这种点源污染为在干旱环境中大规模追踪径流和污染物路径提供了理想的机会条件。拟议的工作旨在利用这一独特的前景来监测暴雨和洪水对水资源的直接影响及其向枯水期的过渡水文调整，并阐明这些事件是否支持资源补充和污染。人口稠密的哈博罗内水库集水区特别令人感兴趣，因为水资源需求和污染源很高，而裂隙基岩中优先的流动路径会导致地下水快速补给和污染。浅层土壤侵蚀影响沉积物和污染物的运移，以及反过来影响补给模式的地貌条件。我们将利用独特的机会，通过将水文监测、时间地球物理成像、地貌测绘和自然示踪实验(渗滤液和稳定水同位素)与模拟相结合的综合方法，评估水量和水质之间的关键联系。实验将跨越正在进行的雨季和向下一个旱季的过渡。水的监测和采样将侧重于整个集水区的现有地面和地表水点，以及不同空间和时间尺度上的大坝和潜在污染源。将数据集整合到模型框架中，将允许表征和量化极端降雨事件对水资源补充和污染的贡献。项目团队由英国和非洲科学家组成，他们在水文地质学、地表水水文学、地球物理和沉积学以及水治理利益攸关方方面具有专业知识。研究将受益于水文监测到位和实物样品收集，这些将在项目期间进行。总体研究成果将是1/1对干旱发展中地区洪水引发的水资源补充和污染的关键过程有更多的了解，2/2水资源利益攸关方提高了适应可预见的水文极端事件增加的管理和政策的能力。产生的新科学将影响对新方法感兴趣的学术界和关于变化下的水文过程的知识，干旱(撒哈拉以南)地区的治理部门需要适应性的水管理战略，能够应对气候变化的短期和长期影响。学生和项目合作伙伴将接受培训，早期职业研究人员将建立他们的研究组合。

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.