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Abstract. The hydrologic cycle behaviour in the Bolivian Altiplano and how it interacts with human activity are still not fully understood. The hydraulic cycle is examined in a novel way in this work by considering extended time series of associated hydrologic and climatic data. Results show that human exploitation and losses from the sewage and water supply networks in the urban areas might cause an hydraulic imbalance in the region. These anthropogenic incomes, at the same time, increase concentrations of different pollutants. Water isotopic analysis reinforces the conceptual model showing that the groundwater sampled are mainly from precipitation. Workshops with local municipalities supported and defined the most relevant anthropic pressures in the basin. This information supports a vulnerability analysis in collaboration among them. The decision-making process for government entities might be strengthened by this study, which would help to develop long-term strategies to prevent and mitigate the issues found in the evaluation of water vulnerability in the region.

<p>The Katari Basin and Minor Lake of Titicaca (Bolivia) is one of the most populated and under pressure basins in the country where approximately 10% of the population lives at the national level (one million inhabitants). Urban development in the basin is rapid and is characterized by poor territorial planning and socio-productive patterns without appropriation in terms of caring for the urban, peri-urban, rural and aquatic environment, which has led, among others, to an accelerated and severe deterioration of water quality throughout the basin. It is for this reason that it is necessary to integrate the management of the productive aspects of the exploitation of its water resources with various environmental and socio-economic aspects of the area.</p><p>This study is within the framework of the "Lake Titicaca Sanitation Program" financed by the Inter-American Development Bank (IDB). The main objective of this program is to contribute to the decontamination of the Katari River basin and MinorTiticaca Lake and generate the necessary conditions to improve the quality of life of the population in this region, which is included in the different actions for the development and implementation of the Katari Basin Master Plan. The Katari Basin Management Unit (UGCK) will be the main beneficiary, which depends directly on the Ministry of Environment and Water (MMAyA) of Bolivia.</p><p>The implementation of a hydrological and hydrogeological model of the Basin would allow us to understand its operation; as well as quantify the general water balance of the Katari Basin and Minor Titicaca Lake. The specific objectives are: (i) Validate the conceptual hydrological model of the Katari basin and minor Titicaca lake; (ii) Update the existing spatial database for later use in the application of the hydrogeological conceptual model of the Katari basin and Minor Titicaca Lake; and (iii) Systematize the conceptual hydrogeological model of the Katari River basin for its integration with the validated surface hydrological model.</p><p>This study has allowed us to analyze the operation model of the Katari aquifers, where all hypotheses and data obtained are justified by consistent calculations. Although the hydrogeological model is considered correct, the information gaps found during the conceptualization process, as well as the results obtained through numerical modeling have shown that it is necessary to go deeper into certain aspects (sampling points inventory, improve hydrochemical monitoring, know the geology in depth in greater detail, among others).</p><p>This conceptual and numerical model, integrating the information available in a single platform, has made it possible to define the evaluation of risks or environmental impacts of the area and provide a frame of reference for other studies or more detailed models.</p>