Lake Titicaca is a crucial water resource in the central part of the Andean mountain range, and it is one of the lakes most affected by climate warming. Since surface evaporation explains most of the lake's water losses, reliable estimates are paramount to the prediction of global warming impacts on Lake Titicaca and to the region's water resource planning and adaptation to climate change. Evaporation estimates were done in the past at monthly time steps and using the four methods as follows: water balance, heat balance, and the mass transfer and Penman's equations. The obtained annual evaporation values showed significant dispersion. This study used new, daily frequency hydro-meteorological measurements. Evaporation losses were calculated following the mentioned methods using both daily records and their monthly averages to assess the impact of higher temporal resolution data in the evaporation estimates. Changes in the lake heat storage needed for the heat balance method were estimated based on the morning water surface temperature, because convection during nights results in a well-mixed top layer every morning over a constant temperature depth. We found that the most reliable method for determining the annual lake evaporation was the heat balance approach, although the Penman equation allows for an easier implementation based on generally available meteorological parameters. The mean annual lake evaporation was found to be 1700 mm year<span classCombining double low line"inline-formula'1</span>. This value is considered an upper limit of the annual evaporation, since the main study period was abnormally warm. The obtained upper limit lowers by 200 mm year<span classCombining double low line"inline-formula">ĝ'1</span>, the highest evaporation estimation obtained previously, thus reducing the uncertainty in the actual value. Regarding the evaporation estimates using daily and monthly averages, these resulted in minor differences for all methodologies.
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Acknowledgements. We would like to express our sincere appreciation to the HASM, Research Programme – Hydrology of Altiplano from Space to Modeling at GET-IRD and IHH-UMSA (Instituto de Hidráulica e Hidrología, UMSA, Bolivia), financed by the TOSCA-CNES (Centre National d’Etudes Spatiales). We would like to thank SENAMHI-Bolivia (Servicio Nacional de Hidrometeorología de Bolivia) for providing long-term climatic data. Thanks also to the IMARPE-Perú (Instituto para el Mar del Perú/Puno) for providing additional hydrological data as well as surface water temperatures of Lake Titicaca. In addition, our acknowledgment is directed to the project Fortalecimiento de Planes Locales de Intervención y Adaptación al Cambio Climático en el Altiplano Boliviano at Agua Sustentable-Bolivia for providing the Lake Titicaca discharge data. Finally, we thank the programme BABEL Erasmus EU for providing economic assistance and completing this work in Sweden.
© Author(s) 2019.