Mapping long-term evapotranspiration losses in the catchment of the shrinking Lake Poopó

Abstract. Lake Poopó is located in the Andean Mountain Range Plateau or Altiplano. A generalised decline in the lake water level has been observed since 2001, coinciding roughly with an intensification of agriculture exploitations such as quinoa crops. Several factors have been blamed for the lake recession, including climate change, increased farming, mining abstractions and population growth. Being an endorheic catchment, evapotranspiration (ET) losses are expected to be the main water output mechanism. This study used a time series of more than 1000 satellite data based products to map ET and vegetation index trends in the Poopó catchment between 2001 and 2014. The aim was to explore the links between ET, vegetation, land use and the lake recession. The years 2015 and 2016 were excluded of the analysis due to the strong impact of El Niño phenomenon over the study area, which could have masked long term temporal trends related to land use.

We quantified the ET losses and vegetation indices for the main cover types in the Poopó catchment and their temporal trends in the study period. It became obvious that cultivated areas were the ones which had experienced the largest increase in water consumption, although they were not in all instances the land covers with the largest losses. This quantification provides essential information for the sustainable planning of water resources and land uses in the catchment.

We also collected on-site and satellite precipitation data. When integrated over the entire catchment, the overall ET losses showed a sustained increasing trend at an average rate of 3.2 mm yr⁻¹. Rainfall water inputs followed a similar trend, with a slightly higher increasing rate of 5.2 mm yr⁻¹. Based on these results and from the point of view of the catchment water balance, the ET loss intensification derived from crop expansion has been compensated by the increase in precipitation. Consequently, this study found no clear link between the agriculture intensification and the Lake Poopó recession in the analysed period.