Posts by Dirk Hoffmann

A Lake in Bolivia Dries Up

Posted by on Feb 25, 2016 in Adaptation, All Posts, Communities, Featured Posts, News | 0 comments

A Lake in Bolivia Dries Up

Spread the News:ShareIn December 2015, while the world’s eyes were on the UN Climate Conference in Paris, Bolivia’s Lake Poopó—once the country’s second-largest lake, with an area of 2700 square kilometers–dried up completely. This event was first recognized by the regional government, located in Oruro, and soon drew national and international concern. This attention has opened a discussion on the causes of this event and on the troubling possibility that the lake may never return to its earlier size. Some people, like Bolivian President Evo Morales, were quick to attribute the drying of Lake Poopó to natural cycles, pointing out that the lake had previously dried out, but always recovered. But others claim that climate change has played a role that will continue into the future, and also note the negative impact of human activities–irrigation schemes and mining activities–which are very unlikely to end.   Based on available documentation and a field visit earlier this month,  we are now in a position to share some preliminary conclusions on what happened to Lake Poopó, as well as to the perspectives for its recovery. The current sharp decline is due most immediately to the strong El Niño event of 2015-16, which has greatly reduced rainfall in the November-March wet season, now reaching its final weeks. But the problem is rooted in long-term processes, which will not be reversed when the current El Niño event ends, most likely later this year. The Physical Environment of Lake Poopó Lake Poopó, like all other lakes, can be characterized by what limnologists–fresh-water ecologists–call a “water balance,” the relation between the water that enters the lake, and the water that leaves it. If unimpeded, a negative water balance will lead to the drying up of a lake. The water balance of Lake Poopó is influenced by its location in a semi-arid area (the average annual precipitation is about 370 mm) and its shallowness (the greatest depth is only 2.4 m). Historically, Lake Poopó receives around two thirds of its water from a sole source, the Río Desaguadero; the remaining third comes from smaller rivers that flow directly into the lake and from rainfall onto the lake’s surface. The Río Desaguadero originates in Lake Titicaca, a large lake that straddles the border between Bolivia and Peru. As this river flows towards Poopó, it receives water from other tributaries, particularly the Río Mauri, an international river whose sources lie in Peru and Chile. Lake Titicaca and the other tributaries of Río Desaguadero receive water from rainfall, snowmelt and runoff from the glaciers on the cordilleras that ring the entire Titicaca-Poopó basin. These sources provide Lake Poopó with water inputs that fluctuate from year to year, reflecting variations in the precipitation that the region receives. A set of locks that were constructed on Lake Titicaca in 2001 could permit the Binational Commission charged with managing the lake to release more water to the Río Desaguadero in dry years, but this possibility has never been realized and, given the water scarcity on the Peruvian side of the Titicaca basin, it seems very unlikely.      Local residents report a decrease in rainfall over the last 10-15 years, a pattern that is confirmed by data from weather stations for the last few decades and by tree-ring records that track rainfall over several centuries. Moreover, glacier retreat has diminished the contribution of meltwater to the lake–a valuable component of the water budget, since it historically compensated in part for the scanty rainfall in dry years. Bolivia has lost about half of its glacier area in the last 40 years, with particularly rapid retreat...

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