Untangling the effects of climate variability and irrigation management on water levels in Lakes Titicaca and Poopó

Many lakes around the world have experienced a reduction in their water levels with consequences for the loss of the ecosystem services they provide locally and regionally such as fisheries, water regulation, biodiversity, drinking water, nutrient and sediment processing, and recreation. In addition, land-use change modifies the regulatory capacity of the contributing areas of lakes. The effects of climate change could worsen this with further reductions in inflows, changes in the temporal regime of precipitation, and increased evaporation due to higher temperatures.

In the central Andes of South America, Lakes Titicaca and Poopó have experienced extreme water level fluctuations. These fluctuations have primarily been attributed to climate variability where repeated El Niño events led to a dramatic reduction in water levels. In the last three decades, Lake Poopó dried up for a few months in 1994, 1995, and 2015. However, uncertainty remains as to the specific causes of fluctuating levels in both lakes.

SEI researchers aimed to quantify the distinct role that irrigation and climate variability have had in the observed range of fluctuation in water levels in Lakes Titicaca and Poopó. To achieve this main objective, they formulated the following research questions:

1. At the basin scale, what are the potential magnitudes and temporal patterns of irrigation withdrawals?
2. What is the impact of withdrawals on the temporal regime of contributing river flows to the lakes?
3. What is the relative contribution of irrigation and climate to the fluctuation of water levels?

The approach used for this study is based on hydrological modeling for the historical period from 1980–2015 with a monthly time step.