Acceleration of glacial melt has severe implications for water-food-energy security and inter-connected livelihoods of vulnerable populations in river basins fed by glaciers. For example, in the Ancash Region of Peru, glacial melt from the Andean Mountains provides up to 67% of dry season water supply going up to 91% during extreme drought (annual average 19%). Rapid retreat of glaciers in the Cordillera Blanca has already had notable impact on that supply, with evidence to suggest the majority of rivers now exhibit decreasing dry-season discharge i.e. have reached and passed 'peak water'. Challenges associated with a reduced supply of water to downstream agriculture, industry and hydropower generation are exacerbated by enhanced sediment and contaminant flux in extreme wet season floods.

Climate change impacts compromise ecosystem service provision at times of both augmented low and high flow. While low flows and water supply are being increasingly impacted by the huge loss of water storage in shrinking glaciers, ENSO-related extreme events are leading to catastrophic delivery of excess water and sediment during high flows which compromise water and environmental quality downstream. Climate change is driving a hydrological regime of extremes with no advantage at either end: from supply and quality issues at low flow to more water than the system can handle at high flow, compromising water and soil quality downstream. Understanding the changing dynamics of glacial melt, hydrology and regional climate change is crucial in order for the design of infrastructure solutions and planning to be effective and resilient.

Responsible, efficient and sustainable water use is necessary in national and transboundary watersheds, to ensure adequate supply and mitigate emerging quality problems. In order to achieve this consultancies and advisory organisations require high quality robust scientific evidence to underpin their design decisions for watershed management. This entails moving from (inefficient) sectorial management of water to a more integrated and holistic approach that takes into account the need for conserving ecosystems services. Indeed, while the Peruvian Congress passed a historic Ecosystem Services law in 2014 to take a holistic approach to tackling these challenges, implementation of integrated action to achieve Sustainable Development Goals has been hampered by a lack of evidence of glacial-fed watershed processes and function. While studies to date have been conducted in the Cordillera Blanca in relation to dynamics of glacial retreat, associated natural disaster risk, hydrology and past glaciations we do not have a sufficiently holistic and integrated knowledge of the wider impacts of glacial melt on current and future ecosystem service provision which is hampered by complexity of human-environment feedbacks, a knowledge base essential for mitigation of future uncertainty and risks.

We propose that a basin-wide understanding of water, sediment and contaminant budgets within Peruvian glacial-fed basins is required to bring policy change for socio-economic benefits through (a) offsetting storage lost from shrinking glaciers through augmentation of mountain ecosystem service provision for landscape water retention and (b) providing the foundation for adaptive management strategies to support and enhance livelihoods under threat from high flows and downstream environmental quality consequences. This research is essential for the design of large-scale energy infrastructure, such as hydropower in glacier-fed regions. Likewise, bringing back and maintaining a balance between sustainable livelihoods and the environment is critical to build community resilience to environmental change.

Potential Impact:
While NGOs and international institutions have begun work on mitigation activities in the Santa Basin and wider glacial-fed basins in Peru, to date their impact has been point-specific, reactive and isolated. The fragmented nature of interventions means potential benefit and improvement to ecosystems and fresh water resource provision are unknown. This underpins the need for the basin-wide approach proposed by this study to catalyse integrated development of adaption policies. Key policy questions remain unanswered; e.g. does transitioning of land use affect water balance and how are these changes augmented/affected by glacier hydrological processes and retreat. These critical scientific-technical gaps are made worse by the lack of tools or strategy to integrate scientific evidence of spatial and temporal dynamics of basin changing basin processes with ecosystem service provision in the water-food-energy security nexus. We aim to close these gaps and bring real change in policy through a combination of stakeholder engagement, training and knowledge exchange activities.

The Pathways to Impact strategy encompasses four key stakeholder groups: (1) national and regional agencies with responsibility for water resource and ecosystem management policy; (2) the water and hydropower industry; (3) third sector NGOs and commercial practitioner companies (e.g. Mott MacDonald) who provide technical, contractual and financial assistance; and (4) Peruvian and UK citizens and taxpayers.

1. National agencies and the management community: MERESE (the Mechanisms for Payments for Ecosystem Services Programme within the Ministry of the Environment) will be able to use the water balance models generated to underpin cases for mountain ecosystems protection and restoration to increase water storage capacity. SERNAMP (the Natural Protected Areas Institute within the Ministry of Agriculture with responsibility for land management policy will benefit in turn through wider ecosystem service provision of such protected and restored landscapes. The Peruvian National Water Authority (ANA) will benefit from water balance models for future resource policy planning, especially within their glaciology unit who are working on impact of retreat on long-term supply.

2. The water and hydropower industry: The Peruvian team have connections into key companies (Chavimochic, Chinecas, Urban Water and Sanitation Services in Huaraz, Chimbote and Trujillo) all of who will benefit from water resource monitoring and modelling data to support future business models and adaption to potential shortage challenges. They are key partners in the co-design and development of a Payment for Ecosystem services model. Hydropower companies are also key stakeholders (e.g. Orazul Energy) in the same way with clear interest in water supply but also siltation behind dams.

3. Third sector NGOs and commercial practitioner companies: have responsibility for implementation of on-the-ground interventions to promote environmental sustainability and associated UN SDGs. They will benefit both from research evidence bases to build local cases for specific intervention and also the channels to discuss and co-design wider policy and PES concept development with the above governmental and industrial partners within project workshops. Similarly, international consultancies and advisory organisations such as Mott MacDonald require high quality, robust scientific evidence to underpin their design decisions for watershed management.

4. The Peruvian and UK public are important stakeholders in the research and also beneficiaries in terms of enrichment of views on environmental management and ecosystem services that this programme will bring. Wider benefits will be achieved through science communication initiatives (e.g. through photojournalism projects and schools liaison).