The deforestation of tropical rainforests reduces the amount of rain in the respective regions. British researchers conclude this from analyzes of satellite data on the Amazon region, the Congo Basin and Southeast Asia. The resulting lack of rainfall not only affects biodiversity, but also reduces agricultural yields and the supply of energy from hydropower.
As the team led by Callum Smith from the University of Leeds reports in the journal "Nature": "Our results offer a compelling argument for the preservation of tropical forests to support regional resilience to climate change".
The team writes that tropical forests moderate the local, regional and global climate through their influence on the water and carbon cycles. Of particular importance for the regional climate is the moisture that evaporates from the leaves of the vegetation: the so-called evapotranspiration. This contributes up to 41 percent of the precipitation in the Amazon Basin, and even up to 50 percent in the Congo Basin.
The current deforestation of tropical forests is changing the balance - in the cleared areas, for example, the decaying plants are increasing carbon dioxide emissions and thus directly climate change. On the other hand, the effects of deforestation on regional precipitation have been less researched.
The team analyzed satellite land-use data for three tropical regions: the Amazon, Congo Basin and Southeast Asia. For the period from 2003 to 2017, it compared the precipitation amounts of deforested areas with those of neighboring intact areas on grids of different sizes, ranging from 5 to 200 kilometers.
In all three regions, increased deforestation was associated with less rainfall, particularly over longer distances. At a distance of 200 kilometers, a reduction in the forest by one percentage point was accompanied by a 0.25 millimeter lower rainfall per month. In Southeast Asia it was 0.48 millimeters per month, in the Amazon region 0.23 millimeters and in the Congo Basin 0.21 millimeters. The team found declines for both the rainy and dry seasons. However, the absolute reductions in precipitation were greatest in the rainy season.
"Climate change is likely to result in increased drought in many tropical regions," the group writes. "This can be further exacerbated by ongoing deforestation." In the Congo Basin, the second largest rainforest on earth after the Amazon region, the loss of forest by 40 percent by the year 2100 could lead to an 8 to 10 percent reduction by the end of the century Rainfalls. The team emphasizes that this is still a very conservative estimate, since tipping points were left out of their calculations, as were the consequences of climate change.
Accordingly, lower precipitation would also affect agricultural production. This could exacerbate the consequences of climate change and periods of drought. In addition, drought can lead to further forest loss and worsen the risk of fire.
And the researchers mention another important point: Their analyzes only cover areas up to a maximum of 200 kilometers away. However, the moisture rising from the forests is transported over far greater distances of up to 2000 kilometers. Therefore, deforestation also has consequences for areas that are several hundred kilometers downwind. These distances were not examined in the study due to a lack of good data, the team points out: "Our analysis probably underestimates the full impact of deforestation on rainfall."
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