Combining global and local models and data for sector-specific water scarcity risk assessments in mega-cities

An increasing number of mega-cities, such as Cape Town and São Paulo, are confronted with increasing droughts as well as an increase in water demand. Inevitably, this leads to an increasing pressure on the available water resources and associated risks and economic impact for the water dependent sectors, such as drinking water supply, industry, energy production, agriculture, and nature.

Here, we present the WaterLOUPE approach (https://deltares.nl/waterloupe) to estimating water scarcity risk for mega-cities and their surrounding catchment that combines the global model PCR-GLOBWB and global datasets (e.g. Shared Socioeconomic Pathways and OECD Economic Outlook) with local datasets and local expert knowledge. Data and models provide the required information to estimate the water scarcity hazard, level of exposure of the relevant sectors and their vulnerability. With our approach we estimate sector-specific risks at the spatial scale of sub-catchments or municipalities. Moreover, the water scarcity risk is provided both for the current situation and future climatic and socio-economic scenarios.

Our approach has been tested, both technically and through stakeholder workshops, in several case studies (São Paolo, Cape Town, Cali, and Tel Aviv-Yafo). The results of our sector-specific water scarcity risk calculations have shown to reflect the local situation of water users in mega-cities very well. As such, the outcomes of the approach have provided a useful knowledge base that enables stakeholders in the catchment to discuss water scarcity risk, which is a first step to collaboration on mitigation and adaptation strategies to decrease water scarcity risks in mega-cities.

Overall, it can be concluded that although climate change tends to decrease water availability, the main drivers of the water scarcity risk are socioeconomical and are related to the strong growth of water demand and the high vulnerability of specific water users. Generally, it was found that water scarcity risks for poor households, small scale farmers, local businesses and nature are relatively high, also under moderate drought conditions. On the other hand, the risks for industries and non-poor households are low to moderate even in more drought prone areas or periods. In most cases the level of water scarcity risk is expected to increase in the future, underlining the urgency for mega-cities to develop actionable and inclusive strategies to mitigate and adapt to the new normal of increasing water stress.