As the UN-Intergovernmental Panel on Climate Change (UN-IPCC) develops a ‘Special Report on Climate Change and Cities’, Stephen Foster, Michael Eichholz, Ricardo Hirata, and Julia Gathu provide insights into what will be required if groundwater is to improve resilience in the face of climate change.
The UN-Intergovernmental Panel on Climate Change (UN-IPCC) is currently developing a ‘Special Report on Climate Change and Cities’ as part of its 7th Assessment Cycle, scheduled for publication in March 2027. It is our view that the recently released technical outline of this document fails to draw attention to the critical importance of groundwater resources for securing urban water supplies within overall climate change adaptation.
Groundwater resources have always displayed excellent drought resilience, and the presence of aquifers (with their large volumes of stored water) offers a ‘natural solution’ for climate change adaptation. The factors that determine the potential role of an aquifer for climate change adaptation are the following:
- Availability of storage – in most aquifers (except karst) this is exceptionally high
- Water supply productivity – water well yields will vary widely with aquifer type
- Water quality – most aquifers contain potable water
- Pollution vulnerability – generally low compared to surface waterbodies.
Resilient water supply planning
There are numerous examples around the world of resilient water supply planning based on the use of groundwater.
Hannover, Germany
The water utility of Hannover (Enercity) provides drinking water to the population of one of the largest metropolitan areas of Germany, with supplies coming mainly from three large wellfields 30 km north of the city in a catchment largely consisting of forest and agricultural land. The aquifer is an unconfined sandy Quaternary deposit with a thickness of around 30 m lying over Cretaceous claystones. The wellfield catchment area of about 300 km2 forms the largest contiguous drinking water protection zone in northern Germany. The water utility has been engaged in proactive groundwater management for many years and has signed cooperative agreements with farmers to reduce fertiliser applications, which have successfully reduced groundwater nitrate concentrations. In addition, groundwater recharge has been enhanced by the conversion of more than 100 km2 of the catchment to mixed forest, resulting in a major increase in recharge rates. A channel has been constructed to divert water from a small river to lower-lying forest areas, where water can infiltrate to the aquifer, and during the winter of 2023/2024 about 2.8 ML was brought to the infiltration area, stabilising local groundwater levels.
Lima, Peru
Lima has considerable water security achieved through rational conjunctive use of river water and groundwater. Despite its hyper-arid location, fast-growing population of more than 8 million, and excessive suspended solids that makes use of its river intake impossible for some months each year, the water utility (SEDAPAL), acting on behalf of national government, has greatly improved water distribution across the city. Groundwater abstraction has been reduced and surface water resources have been improved through a supplementary basin transfer and enhanced riverbed infiltration to groundwater over a 6 km length of the River Rimac.
Bangkok, Thailand
Bangkok has a long history of struggling with the overexploitation of its underlying alluvial aquifers, which from 1980-95 caused land subsidence of almost 1 m. In response, the national groundwater resource agency was granted increased authority to designate critical areas where waterwell drilling would be banned, to close and seal wells in areas where piped water was available, and to implement waterwell licensing and abstraction charging. These measures have reduced groundwater abstraction from 2.3 to 0.8 Mm3/d since 2010, slowed land subsidence, and reduced the risk of seawater flooding.
Enhancing groundwater security
If groundwater systems are to play a role in climate change adaptation, they will need appropriate management, with groundwater resource management requiring strategic rethinking to ensure water supply reliability.
Critical management elements include:
- Improved distribution networks
- Actions to enhance groundwater recharge enhancement
- Actions to ensure that groundwater abstractions consider the need to conserve environmental discharge.
Water resource agencies and community organisations will need to align licensed water well abstraction with climate change pressures and aquifer management measures, including protection strategies and network monitoring that will require increased financial investment. Groundwater resources will also need to be more effectively protected against pollution and salinisation, noting that some anthropogenic pressures are likely to become greater under various climate change scenarios. Significant challenges that need to be confronted at local level include: the control of agricultural practices to reduce excessive leaching of plant nutrients and pesticides; more effective wastewater collection and treatment in areas of rapid urbanisation and industrialisation; and better protection in areas impacted by mining enterprises.
Effective groundwater governance across sectors and administrative boundaries is crucial. All water resource agencies and their corresponding utilities should develop comprehensive future water supply plans, taking into consideration climatic factors and establishing criteria for the reliability of supplies.
Understanding climate change impacts
Considerable uncertainty remains over the long-term effects that climate change will have on groundwater recharge in different climatic regions. More intense rainfall events could increase groundwater recharge in many hydrogeological settings, despite higher temperatures leading to larger soil moisture deficits. However, reduced recharge could impact the reserves of some low storage shallow aquifers in some climatic settings. Climate change is also expected to impact groundwater recharge quality, with recharge after extended dry periods having higher total dissolved solids (TDS), with the converse likely to apply during persistent wet periods. Perhaps the greatest climate change related impact on groundwater will be increased demand for irrigation, which would exert greater pressure to increase groundwater abstraction. Given the current lack of data, more studies need to be undertaken on the long-term effects of climate change on rainfall and the impact on groundwater recharge.
Further reading:
Taylor, R. G. et al.; Ground water and climate change. Nature Climate Change (2013) 3: 322-329.
The authors: Stephen Foster is Visiting Professor, Groundwater Science, at University College London, UK, and IWA Groundwater Management Group Chair; Michael Eichholz is expert for sustainable water management, Enercity, Hannover, Germany, and is a member of IWA’s Groundwater Management Group Steering Committee; Ricardo Hirata is Full Professor at the Institute of Geosciences, Universidade de Sao Paulo, Brazil, and is a member of IWA’s Groundwater Management Group Steering Committee; and Julia Gathu is operations manager at Drilling for Life, Nairobi, Kenya, and is IWA Groundwater Management Group Secretary.
