What is the purpose, usefulness and outcome of climatic simulations, particularly those of ecological LUC measures such as the Sahel afforestation ("Great Green Wall")?
How reliable are they and how can they have an impact on decision making? There are many simulations of the intended afforestation or restoration of the Sahel region, raising warning flags of heat waves and flooding since many years. However, we find that they are based on somewhat unrealistic, hydro-ecologically not feasible vegetational assumptions.
Article Sahel Afforestation and Simulated Risks of Heatwaves and Flo...
Now, after many years of simulations the most recent study (Camara et al, Atmosphere 2022, 13, 421) at least finds that reforestation should help to improve the climate over the reforested area. - Could scientific results have caused delays in starting badly needed restoration measures? Maybe even worse, as an indirect consequence have an affect on drought events?
About 25 years back, a presentation by Moshe Cohen talked of afforestation to a desert climate that in past history was cedars. There efforts of planting individual trees in constructed depressions to capture rain allowed the limited rainfall to grow trees, eventually replenish groundwater and change ephemeral channels to intermittent or perennial. But he was restoring a forest that once existed in his description. Careful determination of native vegetation and trees is important, and in his case, I think he added water to each seedling for a few years to get survival. Extra work or maintenance is sometimes needed in semi-arid conditions and also some other conditions where rainfall or weather patterns are not cooperating to support and achieve restoration. Afforestation when successful can improve soils, infiltration, benefits of transpiration with some cooling effects locally. But if you expect to affect regional climate by afforestation, this would be no small project, and perhaps many years in the development. Where water is limited, grass cover which uses less water in transpiration might be helpful in improving the soils. Gather expertise from botanists, ecologists, soil scientists and historians that might have access to land cover history information that might be useful. It seems harder to restore to a condition that never existed, than to one that has some history.
Dear William, thank you for the very interesting example! And totally agree - yes it seems very important to determine the native vegetation that would or could have been in place before. And as you say this may be long time ago, in case of the Sahara several thousands of years ago. Simulations are showing that, large-scale LUC such as afforestation can have a strong impact on the regional climate, and we may speculate that, if the region is large enough (like a partial continent), also the ww climate could be affected. We find that often these simulations are making generous assumptions of evergreen broadleafed forests to be created as a wide strip in (presently) semi-arid to arid climate zone. Due to ease of computing these dense large-scale afforestations assume a sharp plantation border to hyper-arid desert land over thousands of kilometers. => How realistic can we get with this, and do the results ever have an impact on decision making?
Dear Lorenz Hübner ,
Land related factors contributie to climate change include through carbon dioxide emissions from loss of tropical forest, from degradation of ecosystems and soil; nitrous oxide emissions from excess fertilizer applied in farming; methane emissions from ruminants, rice farming, biomass burning and landfills etc. Responding to climate change involves two possible approaches: reducing and stabilizing the levels of heat-trapping greenhouse gases in the atmosphere (“mitigation”) and/or adapting to the climate change already in the pipeline (“adaptation”).
Thank you Shuraik Kader! these are all important reasons of GHG which contribute to climate change. And there are also the direct effects of vegetation on the socalled "micro climate" - which, e.g. in their sum of large scale afforestation also can contribute to regional (or even global) climate. My question, how can we get to reliable, more realistic simulations of these effects? One way is to assess climatic parameters during a real life afforestation measure, then to extrapolate the observed changes to larger areas. Yet another challenge remaining - you need the original afforestation project to be hydro-ecologically sustainable over the next decades... if possible.
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