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.

Meltwater from glaciers in the Peruvian Andes provides an important and reliable water supply for local and downstream communities for domestic purposes, hydropower, subsistence and commercial agriculture, and industry; and to support rare, high-elevation wetlands and wider ecosystem functioning. However, this long-term, reliable water supply is threatened by increasing temperatures and changing precipitation patterns in the mountainous areas, resulting in shrinking of glaciers and changes in the amount and seasonality of meltwater runoff. A warming climate is also associated with an increasing frequency of extreme hydrological events, such as floods and droughts. Coupled with the stresses of Peru's rapid urbanisation and economic development, these changes are expected to lead to significant water scarcity, with the potential to inhibit economic growth and degrade vulnerable ecosystems (and the services they provide), which in turn will increase social vulnerability, adversely affect the equitable sharing of resources, increase social conflicts, and destabilise Peruvian societies (from local communities to the large coastal urban centres). Peru GROWS aims to increase the resilience of Peruvian communities and ecosystems to hydrological changes arising from shrinking glaciers in the Andes. Working in the Rio Santa catchment - the most glacierised catchment of Peru - we will map the current socio-ecological system to identify where, and how, different communities and ecosystems are exposed to risks from water availability. We will then integrate field measurements and remote-sensing data into physically-based glacier and hydrological models, to simulate the past, present, and possible future changes (to the end of the twenty-first century) to the climate, the glaciers, and to river flows (including amounts, seasonality, and inter-annual variability). In close partnership with local stakeholders, we will exploit this new knowledge to explore the direct and indirect impacts of projected change in glacier behaviour on different communities in the catchment, with a focus on food security, aquatic and terrestrial ecosystems, and energy production. We will provide information on the current state of the water balance and hotspots of potential water scarcity/trade-offs that can be easily understood by key stakeholders and will provide the basis for adaptation planning at local and regional level. Key stakeholders and end-users have been closely involved in the design of Peru GROWS and will co-deliver the research. Two key NGOs, with a long history of work in this region (CARE and the Mountain Institute) as well as social scientists at the National Glacier and Mountainous Ecosystems Research Institute and the Pontifical Catholic University of Peru, will act as an interface with the local stakeholders, especially vulnerable rural communities. Together, they will have a key role in co-designing appropriate adaptation strategies for water resources management and agriculture that will create lasting positive impact. With this, we lay a firm foundation from which multiple impacts can emerge during and after the project.

Glaciers in Peru are undergoing rapid recession in response to climate change and this has helped produce numerous large glacial lakes, many of which are dammed by moraines and are likely to drain catastrophically if the moraine dams fail or are overtopped. A major trigger of lake drainage is rock slides and debris flows into lakes from recently-exposed valley walls and unstable moraines. Glacial Lake Outburst Floods (GLOFs) from these lakes pose a significant hazard to communities and infrastructure and also impact water supplies in the region. In Peru, outburst floods from glacial lakes have caused ~ 32,000 deaths in the 20th century, as well as destroying vital economic infrastructure, settlements and valuable arable land. Despite the importance of these lakes, there are many unanswered questions concerning their future behaviour and the future risk of GLOFs. For instance, we do not know how many glacial lakes there are in Peru, nor whether these are growing in size, nor whether they are becoming more or less vulnerable to rapid drainage caused by rock slides and debris flows. We therefore do not know which lakes might cause GLOFs, nor whether the risk of GLOFs is increasing or decreasing. As a result, this project will answer questions concerning the past, present and future development of glacial lakes and glacier hazards in Peruvian mountains. We will produce the first complete inventory of glacial lakes in all the glaciated mountain regions of Peru, assess their changes in size over time in response to past and future glacier recession and assess changes in their vulnerability to sudden drainage. We will investigate the changing magnitude, frequency, and distribution of GLOFs under current and future global climate change; produce the first complete inventory of historical GLOFs in Peru and identify sites that have the potential to develop glacial hazards in the future. We will, for the first time, assess the risk of landslides into glacial lakes now and into the future. We will use physically-based numerical models to simulate GLOFs at sites identified as posing a high hazard and use these simulations to make hazard and flood risk predictions that can inform decision-makers in Peru. To do this we will focus on five main issues: 1. Glacial lake development and GLOF inventories in the past and present Using literature, remote-sensing and fieldwork, we will compile an inventory of all glacial lakes and past GLOF sites in the glaciated regions of Peru. 2. Climate modelling Use the latest generation of climate models to assess mountain areas of Peru at most risk of future warming and precipitation change. This will enable us to identify areas of future lake drainage risk and we will develop a ranking of mountain areas for future risk of lake drainage. 3. Assessment of lake vulnerability We will identify current and likely future glacier hazards focusing on the developing landslide and debris flow risk as glaciers recede; establish the locations of potential future vulnerable lakes and potential GLOF sites. 4. Model GLOFs. We will (a) establish the physical processes that govern GLOF behaviour; (b) analyse flood hydrographs of selected former GLOFs to establish downstream impacts. 5. Assess the socio-economic effects of GLOFs in Peru and GLOF prediction: We will (a) identify potential GLOF sites across Peru and assess potential socio-economic vulnerability; (b) reconstruct former GLOFs and their impacts; (c) conduct numerical simulations of downstream impacts for potential GLOF sites. This proposal is ODA compliant as it will promote the economic development of Peru by providing improved risk reduction methods that can be applied to hydropower projects and high-altitude mines as well as to local communities through relevant government agencies. The GLOF risk protocols developed in this project can be applied to other DAC-listed countries where GLOF hazards exist (e.g. Argentina)

The anticipated impacts of climate-change induced glacier shrinkage on the water security of mountains and downstream lowlands is a major global concern. However, the connections between climate change, glacier shrinkage, water security and local adaptive capacity are multi-dimensional and non-linear. In many regions of the world including Peru, the physical and human processes that govern them are poorly understood. Therefore, understanding these process, their impacts and implementing adequate science-based adaptation strategies requires an interdisciplinary approach. This approach should combine advancing the state-of-the-art of glaciological and hydrological process understanding, with new insights in current and future levels of water security, human vulnerability, and adaptive capacity. We propose to address this challenge by developing an integrated glacier - water security assessment model to transform our understanding of the impact of glacier shrinkage on water security and to inform policy practices in Peru. We identify the lack of glaciological, hydro-climatological, and water resources data as a major bottleneck to achieve this. Therefore, we propose participatory water resources monitoring as a radically new approach to transform our knowledge of physical processes, constraining water resources models, and supporting evidence-based policy-making. We have assembled a world-leading consortium that combines high-level expertise in field monitoring and computer simulation of glaciers and water resources in Peru, with pioneers of participatory data collection for sustainable development and policy-support. This consortium is ideally placed to generate a breakthrough in data availability on the link between glacier reduction and current and future water security. This is needed to build the next generation of glaciological and hydrological models that can support the design and implementation of adequate climate adaptation strategies. We will use the Vilcanota-Urubamba Basin in southern Peru as our case study. This basin hosts the largest tropical ice cap (Quelccaya) and it is characterised by a very complex water management context and high data scarcity. Our project will follow a "source to tap" paradigm, in which we will deliver the first fully integrated water resources vulnerability assessment framework for glacier-fed basins, comprising state-of-the-art glaciology, hydrology, water demand characterisation, and water security assessment. We will design targeted glacio-hydrological and water resources monitoring campaigns, to complemented existing monitoring efforts of our project partners and collaborators, and new remotely sensed data sets. This campaign will be implemented using the principles and tools of participatory monitoring and knowledge co-creation that our team has pioneered in the tropical Andes. The datasets produced by this approach, combined with existing monitoring implemented by our team and collaborators, will allow us to build an integrated water supply-demand-vulnerability assessment model for glacierized basins, and to use this to evaluate adaptation strategies at the local scale. For the latter, we have engaged with a set of policy stakeholders in Peru that play a key role in the implementation of recent transformative legislation on Peruvian water resources management, and in particular in the new law on the implementation of water funds to invest in catchment interventions (Law 30215). Working directly with these stakeholders will ensure that our approach focuses on locally relevant adaptation strategies, including novel approaches such as the use of nature-based solutions and the restoration of ancestral water "seeding and harvesting practices", thus providing both the scientific basis and the operational tools that support the implementation of this legal framework.

Life on land depends upon freshwater. Mountains act as water towers, producing water by lifting moist air, and by providing temporary surface and below-ground storage of water for later release into rivers. These stores are particularly important in regions that experience seasonal droughts, as snow and ice melt can counteract reduced rainfall during dry spells. Two main natural depots of frozen water exist. Snow is a short-term store, delaying the release of water after snowfall on daily to seasonal timescales. Ice melt also releases water seasonally. However, glacier ice is a longer-term reservoir, storing water for decades to centuries. A similar behaviour can be observed in the non-frozen part of a mountain catchment. Stores such as wetlands, ponds and shallow below-ground flow provide short-term storage, while lakes and deeper groundwater show long-term release characteristics. The combination of these different processes determines the magnitude and behaviour of a mountain range's water tower function for the surrounding area. This is particularly important in the Andes, where some of the most important water towers of the globe are found. The human population in regions neighbouring the Andes depend on mountain water resources for drinking, food production and hydropower, as do animals and plant life. Unfortunately, human-induced climate change is altering the stores of water held in the Andes water towers. Greenhouse gas emissions mean that snow-bearing weather conditions are becoming less frequent, depleting the stocks of snow held in the mountains. The lack of replenishing snow, and increasing temperatures, are causing glaciers to lose the ice they store, retreating to the higher and colder portions of the mountains. In combination with climate change impacts on the rest of the catchment, this is contributing to water shortages across the Andes. Ongoing droughts are hitting high-population cities, where the concentration of people increases the demand for water. For example, the cities of Lima and Huaraz (Peru), La Paz (Bolivia) and Santiago (Chile), are all situated in catchments where snow and ice melt contribute to river flow. However, upstream rural areas, which are less adaptable to climate change, are often even more directly reliant upon snow and ice meltwater. This impacts irrigation for agriculture, stressing the food security of the region. To help manage these changes to water supplies, this project aims to achieve two things. The first is to provide better monitoring. The high altitudes of the Andes are poorly instrumented. To work out where and how fast conditions are changing, we will install more scientific instruments to measure snow, weather and river discharge. To contextualise the changes we can measure now, we need longer observational records extending back in time. Many glaciers have been retreating since 1850, leaving behind an imprint in the landscape which we will map. Using satellite imagery, we can track the retreat of these glaciers from the 1970s to their present position. We will also utilise records of past climate conditions, recorded by sailors in ships-log books and stored in the landscape in sediments. Our second goal is to project future changes, which requires computer models of climate, glacier and river processes. Such projections are required for policy makers, who need to be reliably informed of potential future change. We will combine state-of-the-art models, to simulate the changing water resources in ten Andean catchments. To assess the skill of our models at making predictions, we will test them against our observations of past conditions and current changes. Models that perform well at replicating observed conditions will be used to project a range of possible future climate scenarios. By combining these observational and model-based approaches, we will improve the approach to projecting water resource change, and help to inform water management plans.