WateR security And climate cHange adaptation in PerUvian glacier-fed river basins (RAHU) 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. The Newton Fund builds research and innovation partnerships with developing countries across the world to promote the economic development and social welfare of the partner countries.