Modelling Lake Titicaca's daily and monthly evaporation

Ramiro Pillco Zolá,Frederic Satgé,Luis Mollericon,Lars Bengtsson,José Pasapera,Franck Timouk,Marie-Paule Bonnet,Cesar Gamarra,Belen Martí-Cardona,Ronny Berndtsson

doi:10.5194/hess-23-657-2019

Abstract

Abstract. 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−1. 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−1, 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.

Highlights

Lake Titicaca, the largest freshwater lake in South America, is located in the endorheic Andean mountain range plateau Altiplano, straddling the border between Peru and Bolivia (Fig. 1)
Pillco Zolá et al.: Modelling Lake Titicaca’s daily and monthly evaporation challenge of managing water resources in the Altiplano Basin is further exacerbated by climate conditions; annual rainfall is highly variable (Garreaud et al, 2003), while warming in this region exceeds the average global trend (López-Moreno et al, 2015), which is expected to intensify the evaporation from the lake surface and the evapotranspiration losses from the whole basin
Since convection from the surface layer is intense during nights, resulting in a well-mixed top layer every morning, it is possible to determine the change of heat storage from the measured morning surface temperature

Summary

Introduction

Lake Titicaca, the largest freshwater lake in South America, is located in the endorheic Andean mountain range plateau Altiplano, straddling the border between Peru and Bolivia (Fig. 1). Pillco Zolá et al.: Modelling Lake Titicaca’s daily and monthly evaporation challenge of managing water resources in the Altiplano Basin is further exacerbated by climate conditions; annual rainfall is highly variable (Garreaud et al, 2003), while warming in this region exceeds the average global trend (López-Moreno et al, 2015), which is expected to intensify the evaporation from the lake surface and the evapotranspiration losses from the whole basin. The combined impact of these pressures becomes evident at the downstream end of the system, where Lake Poopó is situated In recent years this lake suffered extreme water shortages, including its complete drying out in December 2015 (Satgé et al, 2017)

Methods

Results

Conclusion