Emerging water scarcity risks in tropical Andean glacier-fed river basins

In the tropical Andes and adjacent lowlands, human and natural systems often rely on high-mountain water resources. Glaciated headwaters play an essential role in safeguarding water security for downstream water use. However, there is mounting concern particularly about long-term water supply as the timing and magnitude of glacier meltwater contribution to river streamflow become less reliable with rapid glacier shrinkage. This concern matches an increase in water demand from growing irrigation, population and hydropower capacity in combination with high social-ecological vulnerabilities threatening sustained water security. Despite important progress in assessing the impacts of glacier shrinkage and consequences for meltwater availability, little is known about the associated hydrological risks and how they propagate downstream. Therefore, integrated approaches are needed that combine a detailed picture of the meltwater propagation through the terrestrial water cycle with human vulnerabilities and exposure to water scarcity. However, the complex topographic and sociocultural setting including scarce data, limited local capacities and frequent water conflicts hamper a more thorough process understanding and water security assessment at a basin scale.

Under high complexity and uncertainty, we propose a coupled risk framework combining water scarcity hazards, exposed people and multiple human vulnerabilities to address these limitations. An important aspect of the framework is the recognition of knowledge from indigenous and rural communities that can potentially be integrated into current scientific baselines and innovative adaptation debates. Our framework interlinks a broad set of hydroclimatic, socioeconomic and water management variables at unprecedented detail. We put particular emphasis on the quantification and understanding of multidimensional vulnerabilities as a key element for evaluating the enabling effects of these impacts in social-environmental systems. However, the assessment of corresponding vulnerabilities might not be relevant if the degree of the systems’ exposure is not sufficiently addressed. Therefore, we further analyse the interplay of the diverse variables and critical system thresholds that determine the dimensions and spatiotemporal patterns which enable meaningful assessments of cascading processes and interconnected risks to water scarcity.

Our risk framework provides a thorough baseline to support assessments of future water availability for guiding climate change adaptation, water management, and governance in rapidly changing mountain basins. Nonetheless, remaining uncertainties and limited understanding relate to the availability of local data and highlight the need for additional data collection. Lastly, we identify specific opportunities to explore the use of nature-based solutions, such as source water and wetland protection, in combination with a strong engagement of local communities and policy makers as an efficient pathway to cope with emerging risks to water scarcity in glacier-fed river basins.