European Rainfall Will Be Boosted By Planting More Trees, Study Finds

The researchers believe extra rain could combat the rise in dry conditions—a side effect of climate change.

Heavy rain in the mountains

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A new study published in Nature has highlighted the impacts planting new trees across Europe will bring to rainfall in the continent.

The study used empirical statistical analysis to take a look at the impact of reforestation or afforestation on agricultural land. It shows that planting more trees will have profound impacts on rainfall across the region. 

More rainfall may seem like an unambiguously good thing. But as the researchers note, this increased rainfall could bring both positive and negative effects for different regions across Europe. In some areas, increased rainfall will be most welcome. In other areas, however, it may not be quite as much of a boon.

Taking a look at this study can help us understand why tree planting can be a complex business, with impacts that should be carefully considered before broader decisions are taken about how and where tree planting takes place. Looking deeply into the role trees play in the world's water cycle and precipitation will be vital as we seek to mitigate the effects of, and adapt to, our climate crisis. 

Increased Rainfall

Researchers found that a uniform 20% increase in forest across Europe would boost local rainfall. Greater impact, according to their models, would be felt in coastal areas. 

This study found there was a local increase in precipitation following forestation, in particular in winter. 

Not only does planting trees impact the immediate area. It also has profound implications for rainfall figures far downwind of the new forests. Forests are estimated to increase downwind precipitation in most regions during summer. By contrast, the downwind effect in winter is positive in coastal areas but near neutral and negative in Continental and Northern Europe, respectively.

Combining the estimations for local and downwind rainfall, the researchers found that converting farmland to forest would increase summer rainfall by, on average, 7.6%. 

Reasons for the Increased Rainfall

The turbulence over forested land, which has greater roughness than agricultural land, and increased evaporation and transpiration are believed to be factors in the role of forests in increasing rainfall across a region. Forests typically sustain higher evapotranspiration than agricultural land, especially during the summer season. 

Forestation also warms the land surface during winter but cools it during summer, which researchers believe also helps to account for the seasonal cycles. Warmer temperatures at the land surface destabilize the planetary boundary layer, thereby favoring the creation of rainfall. 

Positive and Negative Impacts

This study highlights an important factor in reforestation and afforestation efforts. Since planting more trees can bring more rainfall, even far from the planting site and even in neighboring countries, all the impacts of potential schemes must be considered on a broad scale. And the location for new tree planting must always be carefully considered. 

In areas of Southern Europe, around the Mediterranean in particular, increased precipitation will be most welcome. It will be important as these regions seek to adapt to the hotter, drier summers that climate change will bring. Though it should be noted that effects may not be uniform even across this region, and some areas may even experience greater water stress as a result of reforestation schemes. 

It is important to note that increased rainfall following tree planting could also bring negative impacts in areas where extreme rain events are becoming more of a threat due to climate change. Boosting rainfall patterns may not be a good thing in Atlantic regions that have already experienced flooding events due to global warming. 

This shows that combatting climate change with trees is not as simple as some people make out. Careful consideration of land use is key, with joined up thinking across broader bioregions to maximize positive impacts and minimize negative results. 

Forestation can bring a huge range of benefits in climate change mitigation and adaptation, of course. But joined-up thinking is essential. And it is important to look at all the potential impacts, locally and in the broader region, of any reforestation or afforestation scheme. 

It is also important to note that the climate crisis needs more of a response than just tree planting. We need to consider not only how to sequester carbon and mitigate negative environmental effects, but also to halt ongoing emissions, and keep fossil fuels in the ground. 

View Article Sources
  1. Meier, Ronny, et al. "Empirical Estimate of Forestation-Induced Precipitation Changes in Europe." Nature Geoscience, vol. 14, no. 7, 2021, pp. 473-478., doi:10.1038/s41561-021-00773-6