Deforestation of Amazon warms local climate

The loss of forest cover in the Amazon has a significant impact on the local climate in Brazil, according to a new study by LEAF scientists in the School of Earth and Environment.

Using satellite data, Dr Jess Baker and Professor Dominick Spracklen explored the impact of deforestation in the Amazon between 2001 and 2013. Looking at key climatic indicators, they found that deforestation causes the local climate to warm – and that the warming intensified as the severity of deforestation increased.

“The recent Amazon wildfires have reminded us all of the important role that forests play in our global systems. But it cannot be overlooked that intact Amazon forests are also crucially important for Brazil’s own local climate.” said study lead author Dr Jess Baker.

Forests control the exchange of moisture and energy between the land surface and the atmosphere above them. The Earth’s surface absorbs energy from the Sun; this energy can be used to help water at the surface evaporate (i.e., evapotranspiration or latent heat) or, it will warm the air directly (i.e., sensible heat). The presence of trees and other vegetation draws moisture from the soil, allowing the Sun’s energy to be used for evapotranspiration. When forests are removed or degraded, the balance between these fluxes is disturbed and the local air warms (see video below for more on water cycles above forests and the impact of deforestation).

“Deforestation decreases the amount of water emitted to the atmosphere from the forest through a process called evapotranspiration.” said study co-author Dominick Spracklen, Professor of Biosphere-Atmosphere Interactions. “Evapotranspiration can be thought of as the forest ‘sweating’; when the moisture emitted by the forests evaporates it cools the local climate. Deforestation reduces evapotranspiration, taking away this cooling function and causing local temperatures to rise. As temperatures rise this increases drought stress and makes forests more susceptible to burning.” he added.

Clear relationships between the amount of disturbance experienced by a forest, and changes to local climatic variables were observed in the new study. Forests that experienced less than 5% canopy loss over the decade analysed (called “intact” forests) were found to have the most stable climates, showing only small increases in temperature. Areas that had tree cover reduced to below 70% warmed almost half a degree Celsius more than the neighbouring intact forests during the study period.

The differences between intact and disturbed forests were most pronounced during the driest part of the year, when temperature increases of up to 1.5°C were observed in areas affected by severe deforestation. This increase is additional to global temperature rises driven by climate change.

“A healthy intact Amazon forest helps regulate the local climate and can even act as a buffer to the warming effects of climate change, compared with disturbed forests.” added Dr Baker.

Read the full study here.