What is the cause of the water shortage in Bogotá? The Amazon, a key factor

In Colombia, all municipalities are at some risk of being affected by climate change. But for Bogotá, the situation is more complex, since it is not only the most populous city in the country, but also the second most threatened, according to the "Analysis of vulnerability and risk due to climate change for the municipalities of Colombia", a report presented by Ideam and the United Nations Development Program (UNDP).

As Mayor Carlos Fernando Galán announced this week, the city will have to return to weekly water rationing because the rains have been lower than expected and the Chingaza system has not been filled to the predicted levels, so that at the current rate of consumption it would not be enough to meet the needs of the more than 10 million people it serves until next April (when the rains return). This system of reservoirs has a peculiarity: although it supplies a city located in the Andes, it depends on the rains that fall in the Orinoquia, and this hydrological regime is undoubtedly changing.

Bogotá's water depends to a large extent on the existence of two types of ecosystem: the páramos, which act like sponges, collecting and managing rainfall, retaining more water when there is a surplus and slowly releasing it when there is a drought; and the Amazon jungle, which, through evapotranspiration, creates the so-called 'flying rivers', huge clouds laden with rain that move from the south of the country and cross the entire continent, leaving water, lots of water, in their wake.

Research by the Universidad Escuela Colombiana de Ingeniería Julio Garavito and the Empresa de Acueducto y Alcantarillado de Bogotá has found that 93 per cent of the humidity that reaches Chingaza comes from neighbouring regions, of which the Amazon provides 23.7 per cent, mainly between June and August, and the Orinoquia 25.2 per cent, mainly from January to April. The rest of the moisture comes from different regions, albeit in smaller proportions. The researchers also discovered something that many scientists have been warning about for years: the high rate of deforestation.

The study also found that the situation is complicated when phenomena such as El Niño and La Niña occur, exacerbating droughts in some areas of the country and increasing rainfall in others. This year, for example, a weak Niña is expected to begin in October, which will increase rainfall in the Andes and the Caribbean, but have the opposite effect in the Orinoquia, where much of Bogotá's water is collected.

But the lack of rainfall is not the only threat Bogotá will face if its green forests continue to be destroyed. The climate crisis will also bring other complications to the city, such as more intense floods or more frequent forest fires, the creation of urban heat islands, and less productive agriculture. And the situation will become even more critical in times when the country experiences El Niño or La Niña phenomena, as it did this year.

According to Benjamín Quesada, climatologist and director of the Earth System Science program at the Universidad del Rosario, the equation is not only simple, but has been studied for more than ten years: every time we cut down a forest, we reduce rainfall not only in Bogotá, but throughout the country and the region. "In fact, deforestation has a much greater impact on the water cycle than on temperature. Every time we cut down a forest, we reduce rainfall," says Quesada.

The expert emphasizes that not only are we depriving the forests of their natural capacity to evapotranspire, that is, to exchange water with the atmosphere through their leaves, but it has also been discovered that when the trees are cut down, the remaining ecosystem absorbs less energy because it reflects the solar radiation it receives, which means it has less capacity to do its job of regulating the flow of water.

Meanwhile, according to Carlos Devia, Doctor of Engineering and Professor at the Faculty of Environmental and Rural Studies of the Javeriana University, in addition to the loss of forests, there are other factors that aggravate the situation of serious rainfall deficit in the country's capital, such as the global increase in temperatures and the change in regional atmospheric dynamics; All this, added to the fact that we have less and less swamps to retain water and less rainforest to evapotranspire, generate the perfect cocktail for the climatic situation to become more critical, to such an extent that predicting the behavior of the climate has become more difficult.

"Predicting the effects of climate change at this point in time is the least accurate, and it is best to prepare for the worst. The closest evidence is the prediction of La Niña, which has not arrived, and the current rainfall is below the expected average. In other words, we must consider not depending on rainfall for our water supply, which should not overshadow our responsibility to reduce greenhouse gases. The city must become carbon neutral as soon as possible, and a fee should be included in the bills to restore the tree cover lost in the Colombian Amazon. In Bogotá we have been living on water that we have not paid for, it is time to pay for its production, and this is happening in the forested areas of the Andes and the Amazon," the researcher emphasizes.

For him, it is urgent that the city and the country take measures to restore and protect the forests that we have cut down and to protect those that remain, actions that go beyond istrative borders. "We must effectively protect the remaining forests and ensure that they are not lost due to social and even environmental conditions. The social ones are related to logging to turn them into pastures, and the environmental ones are related to climate change, which causes the death of these trees and favors forest fires. In other words, if we stop logging, these forests will be lost because the "environment" is leading them to this situation, and this is where we have to act. At the same time, we must guarantee the recovery of the lost tree cover, that is, the areas that used to be forests and are now pasture or crops, must be converted into areas with trees," says Devia.

Diego Restrepo, a consultant in water sciences and adaptation to climate change, agrees, adding that the great risk today is that the Amazon will cross the so-called "tipping point" and become a savanna, which would undoubtedly completely change the rainfall and climate regime of the entire planet. This risk, moreover, is very imminent.

"The big concern about the Amazon turning into a savanna and crossing that tipping point is that no matter how much we reforest, it will be impossible for it to return to its former state. What the scientific studies say is that this transition from Amazon forest to savanna would occur if the planet warmed by an average of 3°C to 5°C, but that is if the Amazon were completely healthy and complete. There are studies that indicate that if the Amazon is deforested by between 20% and 25%, this tipping point temperature would be reduced to between 1.5°C and 2°C. In other words, if we deforest 20-25% of the Amazon and the global temperature rises 1.5°C to 2°C, the rainforest would turn into savannah. Today we are at 1.2°C of warming and 17% of deforestation. In other words, we are very, very close to the tipping point," he says.

Restrepo emphasizes that it is not only the ecosystems of the Amazon and the Andes that must be protected, but there is a group of key points for the climate regulation of the planet that would also change the rainfall of the country and the planet in case of reaching a tipping point like the one that the Amazon is currently facing. These include, for example, the glaciers of Argentina, the Atlantic Meridional Current, and the Arctic ice.

“For example, the Atlantic Ocean current is weakening, and if that current weakens, the climate changes completely in Europe, which would become much colder despite the fact that the entire planet is warming, because what that current does is to recirculate heat throughout the year on the planet, and that is also connected with the Amazon, with the areas of Siberia, with the poles. There are some key ecosystems that, if affected, completely change the planet. What this shows is that everything is connected and we have to think a lot about planetary stability beyond the local level, because at the planetary level we depend on the rest of the ecosystems”, concludes the expert.

EDWIN CAICEDO

Periodista de Medioambiente y Salud

@CaicedoUcros