• Energy Research

Although shallow groundwater (<50 mbgl) sustains the vast majority of improved drinking-water supplies in rural Africa, there is little information on how resilient this resource may be to future changes in climate. This study presents results of a groundwater survey using stable isotopes, CFCs, SF6, and 3H across different climatic zones (annual rainfall 400–2,000 mm/year) in West Africa. The purpose was to quantify the residence times of shallow groundwaters in sedimentary and basement aquifers, and investigate the relationship between groundwater resources and climate. Stable-isotope results indicate that most shallow groundwaters are recharged rapidly following rainfall, showing little evidence of evaporation prior to recharge. Chloride mass-balance results indicate that within the arid areas (<400 mm annual rainfall) there is recharge of up to 20 mm/year. Age tracers show that most groundwaters have mean residence times (MRTs) of 32–65 years, with comparable MRTs in the different climate zones. Similar MRTs measured in both the sedimentary and basement aquifers suggest similar hydraulic diffusivity and significant groundwater storage within the shallow basement. This suggests there is considerable resilience to short-term inter-annual variation in rainfall and recharge, and rural groundwater resources are likely to sustain diffuse, low volume abstraction.

AbstractClimate change and urbanization can increase pressures on groundwater resources, but little is known about how groundwater quality will change. Here, we use a global synthesis (n = 9,404) to reveal the drivers of dissolved organic carbon (DOC), which is an important component of water chemistry and substrate for microorganisms that control biogeochemical reactions. Dissolved inorganic chemistry, local climate and land use explained ~ 31% of observed variability in groundwater DOC, whilst aquifer age explained an additional 16%. We identify a 19% increase in DOC associated with urban land cover. We predict major groundwater DOC increases following changes in precipitation and temperature in key areas relying on groundwater. Climate change and conversion of natural or agricultural areas to urban areas will decrease groundwater quality and increase water treatment costs, compounding existing constraints on groundwater resources.

Groundwater is a critical resource enabling adaptation due to land use change, population growth, environmental degradation, and climate change. It can be a driver of change and adaptation, as well as effectively mitigate impacts brought about by a range of human activities. Groundwater quality is key to assessing groundwater resources and we need to improve our understanding and coverage of groundwater quality threats if we are to use groundwater sustainably to not further burden future generations by limiting resources and/or increasing treatment or abstraction costs. Good groundwater quality is key to progress on a range of Sustainable Development Goals, but achievement of those goals most affected by groundwater contamination is often hindered by of a lack of resources to enable adaptation. A range of threats to groundwater quality exist, both natural and anthropogenic, which may constrain groundwater use. However, groundwater often provides good quality water for a range of purposes and is the most important water resource in many settings. This special issue explores some of the key groundwater quality challenges we face today as well as the opportunities good groundwater quality and treatment solutions bring to enhance safe groundwater use. Legacy anthropogenic contaminants and geogenic contaminants may be well documented in certain places, such as N America, Europe and parts of Asia. However, there is a real issue of data accessibility in some regions, even for more common contaminants. This paucity of information can restrict our understanding and ability to manage and protect groundwater sources. Compared to surface water quality, large scale assessments for groundwater quality are still scarce and often rely on inadequate data sets. Better access to existing data sets and more research is needed on many groundwater quality threats. Identification and quantification of these threats will support the wise use and protection of this subsurface resource, allow society to adequately address future challenges, and help communities realise the full potential of groundwater.

Riverbank filtration schemes form a significant component of public water treatment processes on a global level. Understanding the resilience and water quality recovery of these systems following severe flooding is critical for effective water resources management under potential future climate change. This paper assesses the impact of floodplain inundation on the water quality of a shallow aquifer riverbank filtration system and how water quality recovers following an extreme (1 in 17 year, duration >70 days, 7 day inundation) flood event. During the inundation event, riverbank filtrate water quality is dominated by rapid direct recharge and floodwater infiltration (high fraction of surface water, dissolved organic carbon (DOC) >140% baseline values, >1 log increase in micro-organic contaminants, microbial detects and turbidity, low specific electrical conductivity (SEC) 400% baseline). A rapid recovery is observed in water quality with most floodwater impacts only observed for 2-3 weeks after the flooding event and a return to normal groundwater conditions within 6 weeks (lower fraction of surface water, higher SEC, lower DOC, organic and microbial detects, DO). Recovery rates are constrained by the hydrogeological site setting, the abstraction regime and the water quality trends at site boundary conditions. In this case, increased abstraction rates and a high transmissivity aquifer facilitate rapid water quality recoveries, with longer term trends controlled by background river and groundwater qualities. Temporary reductions in abstraction rates appear to slow water quality recoveries. Flexible operating regimes such as the one implemented at this study site are likely to be required if shallow aquifer riverbank filtration systems are to be resilient to future inundation events. Development of a conceptual understanding of hydrochemical boundaries and site hydrogeology through monitoring is required to assess the suitability of a prospective riverbank filtration site.

La nécessité d'élaborer des stratégies d'adaptation au changement climatique en Afrique devient critique. Par exemple, les infrastructures à longue durée de vie doivent maintenant être conçues ou adaptées pour tenir compte d'un climat futur qui sera différent du passé ou du présent. Il est de plus en plus nécessaire que les informations climatiques utilisées dans la prise de décision passent des mesures traditionnelles axées sur la science aux mesures axées sur la décision. Cela est particulièrement pertinent en Afrique de l'Est, où l'adaptation et les capacités socio-économiques limitées rendent cette région extrêmement vulnérable au changement climatique. Ici, nous utilisons un processus de consultation interdisciplinaire pour définir et analyser un certain nombre de ces mesures orientées vers la décision. Ces indicateurs adoptent une approche holistique, abordant les principaux secteurs d'Afrique de l'Est de l'agriculture, de l'approvisionnement en eau, de la pêche, de la gestion des inondations, des infrastructures urbaines et de la santé urbaine. Une analyse multiforme des projections climatiques multimodèles fournit ensuite un référentiel d'informations axées sur l'utilisateur sur le changement climatique et ses incertitudes, pour toutes les métriques et saisons et deux horizons temporels futurs. Le caractère spatial et la grande incertitude intermodulaire des changements dans les mesures de température et de précipitations sont décrits, ainsi que ceux d'autres mesures pertinentes telles que l'évaporation et le rayonnement solaire. Les relations intermodales entre les métriques sont également explorées, avec deux groupes clairs se formant autour des métriques de pluie et de température. Cette dernière analyse détermine dans quelle mesure les pondérations du modèle pourraient ou ne pourraient pas être appliquées à plusieurs mesures climatiques. Les travaux ultérieurs doivent maintenant se concentrer sur la maximisation de l'utilité des projections du modèle et sur le développement de stratégies de communication adaptées basées sur les risques. La necesidad de desarrollar estrategias de adaptación al cambio climático en África se está volviendo crítica. Por ejemplo, las infraestructuras con una larga vida útil ahora deben diseñarse o adaptarse para tener en cuenta un clima futuro que será diferente del pasado o del presente. Existe una necesidad creciente de que la información climática utilizada en la toma de decisiones cambie de las métricas tradicionales impulsadas por la ciencia a las métricas impulsadas por la decisión. Esto es particularmente relevante en África Oriental, donde la adaptación y la capacidad socioeconómica limitadas hacen que esta región sea muy vulnerable al cambio climático. Aquí, empleamos un proceso de consulta interdisciplinario para definir y analizar una serie de métricas orientadas a la toma de decisiones. Estas métricas adoptan un enfoque holístico, abordando los sectores clave de África Oriental de la agricultura, el suministro de agua, la pesca, la gestión de inundaciones, la infraestructura urbana y la salud urbana. Un análisis multifacético de las proyecciones climáticas multimodales proporciona un repositorio de información centrada en el usuario sobre el cambio climático y sus incertidumbres, para todas las métricas y estaciones y dos horizontes temporales futuros. Se describe el carácter espacial y la gran incertidumbre intermodal de los cambios en las métricas de temperatura y precipitación, así como las de otras métricas relevantes como la evaporación y la radiación solar. También se exploran las relaciones intermodales entre las métricas, con dos grupos claros que se forman alrededor de las métricas de lluvia y temperatura. Este último análisis determina la medida en que las ponderaciones del modelo podrían, o no, aplicarse a través de múltiples métricas climáticas. El trabajo adicional ahora debe centrarse en maximizar la utilidad de las proyecciones de modelos y desarrollar estrategias de comunicación basadas en el riesgo a medida. The need for the development of adaptation strategies for climate change in Africa is becoming critical. For example, infrastructure with a long lifespan now needs to be designed or adapted to account for a future climate that will be different from the past or present. There is a growing necessity for the climate information used in decision making to change from traditional science-driven metrics to decision-driven metrics. This is particularly relevant in East Africa, where limited adaptation and socio-economic capacity make this region acutely vulnerable to climate change. Here, we employ an interdisciplinary consultation process to define and analyse a number of such decision-oriented metrics. These metrics take a holistic approach, addressing the key East African sectors of agriculture, water supply, fisheries, flood management, urban infrastructure and urban health. A multifaceted analysis of multimodel climate projections then provides a repository of user-focused information on climate change and its uncertainties, for all metrics and seasons and two future time horizons. The spatial character and large intermodel uncertainty of changes in temperature and rainfall metrics are described, as well as those of other relevant metrics such as evaporation and solar radiation. Intermodel relationships amongst metrics are also explored, with two clear clusters forming around rainfall and temperature metrics. This latter analysis determines the extent to which model weights could, or could not, be applied across multiple climate metrics. Further work must now focus on maximising the utility of model projections, and developing tailored risk-based communication strategies. أصبحت الحاجة إلى وضع استراتيجيات للتكيف مع تغير المناخ في أفريقيا ملحة. على سبيل المثال، تحتاج البنية التحتية ذات العمر الطويل الآن إلى تصميمها أو تكييفها لمراعاة المناخ المستقبلي الذي سيكون مختلفًا عن الماضي أو الحاضر. هناك ضرورة متزايدة لتغيير المعلومات المناخية المستخدمة في صنع القرار من المقاييس التقليدية القائمة على العلم إلى المقاييس القائمة على القرار. وهذا مهم بشكل خاص في شرق أفريقيا، حيث يجعل التكيف المحدود والقدرة الاجتماعية والاقتصادية هذه المنطقة عرضة بشدة لتغير المناخ. هنا، نستخدم عملية تشاور متعددة التخصصات لتحديد وتحليل عدد من هذه المقاييس الموجهة نحو اتخاذ القرار. تتخذ هذه المقاييس نهجًا شاملاً، حيث تتناول القطاعات الرئيسية في شرق إفريقيا وهي الزراعة وإمدادات المياه ومصايد الأسماك وإدارة الفيضانات والبنية التحتية الحضرية والصحة الحضرية. ثم يوفر تحليل متعدد الأوجه للتوقعات المناخية متعددة النماذج مستودعًا للمعلومات التي تركز على المستخدم بشأن تغير المناخ وشكوكه، لجميع المقاييس والمواسم واثنين من الآفاق الزمنية المستقبلية. يتم وصف الطابع المكاني وعدم اليقين الكبير بين النماذج للتغيرات في مقاييس درجة الحرارة وهطول الأمطار، بالإضافة إلى المقاييس الأخرى ذات الصلة مثل التبخر والإشعاع الشمسي. كما يتم استكشاف العلاقات بين النماذج بين المقاييس، مع تشكيل مجموعتين واضحتين حول مقاييس هطول الأمطار ودرجة الحرارة. يحدد هذا التحليل الأخير مدى إمكانية أو عدم إمكانية تطبيق أوزان النموذج عبر مقاييس مناخية متعددة. يجب أن يركز المزيد من العمل الآن على تعظيم فائدة إسقاطات النموذج، وتطوير استراتيجيات اتصال مخصصة قائمة على المخاطر.