Tree planting is often mentioned in scientific studies as an important way to tackle climate change. The idea is simple: As trees grow they absorb and store carbon dioxide, thereby reducing its concentration in the atmosphere. But the benefits from trees don’t stop there, as shown by Danijel Belušić and colleagues from the Rossby Centre at SMHI in a paper published in Environmental Research Letters.
Long-term effects of changing forest cover
Extratropical cyclones cause up to 80 percent of precipitation extremes in some regions of Europe with a large societal and economic impact. The study focuses on the long-term effects of changing forest cover on extratropical cyclones over Europe and consequently on local climate. Using a regional climate model and a cyclone-tracking algorithm, Rossby Centre’s researchers investigated long-term changes in the number and intensity of cyclones, and their effect on precipitation, under conditions of deforestation and complete afforestation.
Changes of forest cover considerably and consistently affect the number and intensity of cyclones over land, the study finds. Afforestation reduces the number and intensity of cyclones everywhere over Europe compared to experiments with smaller forest cover.
“The increased roughness due to forests spins down a cyclone and reduces its intensity,” says Danijel. The reduction generally increases from west to east over the continental area, ranging from less than 20 percent to 80 percent. This is because cyclones predominantly travel eastward and are thus longer exposed to land cover effects further east.
With weaker and fewer cyclones, extreme precipitation in winter is found to decrease up to 25 percent for afforestation compared to deforestation. At the same time the winter weak and moderate precipitation increases sufficiently to balance the precipitation loss from the decrease in extremes. Additionally, in southern and eastern Europe there is an increase in precipitation predominantly in summer for the afforestation scenario:
“Due to the increased evapotranspiration, the atmosphere receives more moisture from the surface which can be converted into clouds and precipitation”, clarifies Danijel.
Afforestation reduces extreme precipitation events
In light of the recent studies showing the changing nature of cyclones over Europe, where intensely precipitating cyclones could triple by the end of the century, afforestation could provide an efﬁcient way of reducing the intensity and frequency of extreme precipitation events. At the same time, the widely-documented decrease of summer precipitation in the Mediterranean region in a warmer climate could be mitigated by the increase in precipitation with afforestation.
This study has attracted the attention of the international media, being featured in The Guardian, Physics Today and IPS.