\n<\/strong>Through the process of evapotranspiration, forests help recycle moisture that has blown in from seas and fallen as rain. Trees<\/a> pump moisture from the soil back to the atmosphere, where it then condenses again and falls as rain, hundreds or even thousands of kilometers downwind.\u00a0Water<\/a> vapor\u00a0released by forests can travel as far as 2,000 km away in the tropics and as far as 5,000 km in the temperate zone. In parts of the\u00a0Western Amazon Basin, up to 50% of annual precipitation originates from the forest itself; up to 70% late in the\u00a0dry season.<\/strong><\/p>\n
Given the important role forests have in recycling rainfall, removing them can disrupt rainfall patterns within and across national boundaries. In\u00a0Borneo, watersheds that had lost more than 15% of their forests<\/a> between 1973 and 2007 had a greater than 15% reduction in rainfall during that time. A model of deforestation in the Amazon predicted that if\u00a0deforestation\u00a0continues on its current trajectory, average annual rainfall by 2050 would drop by 8.1% across the region.<\/p>\n Can Forest Restoration Restore Rainfall? One recent study showed that following the Chinese government\u2019s<\/a> massive\u00a0Green for Grain\u00a0program \u2014 the largest afforestation program in the world, where trees were planted on retired farmlands to reduce flooding and soil erosion \u2014 precipitation increased by 58%, or an average 54.62 mm per year over the afforested area. After trees were planted, atmospheric moisture entering the region decreased, but the amount of moisture falling as rain increased, as did the proportion of fallen rainfall that was recycled into future rainfall over the region.<\/p>\n In addition, several models predict that increasing tree cover would also increase precipitation. For example, models show that restoring\u00a0Australia\u2019s\u00a0savanna ecosystems (which include trees) would increase rainfall by almost 10%, while increasing forest cover in\u00a0Europe\u00a0would increase average downwind precipitation by 7.6% during the summer months.<\/p>\n For the tropics, models predict that reforestation over the\u00a0Sahel\u00a0region could increase rainfall locally and downwind, increasing the intensity of heavy rain events, shortening the length of the dry season, and\u00a0reversing\u00a0the Niger River Basin\u2019s overall drying trend. Contributors to the\u00a0Science Panel for the Amazon, a leading authority on scientific, economic and moral issues related to conservation of the Amazon, anticipate that \u201cforest restoration<\/a> could help the Amazon maintain its hydrological integrity, with evapotranspiration from restored forests contributing to the east-west transfer of moisture.\u201d<\/p>\n The Relationship Between Forests and Local Temperatures In the Brazilian Amazon and Cerrado, researchers have detected the effects of deforestation on increased daily temperatures up to 50 km away from\u00a0deforested\u00a0areas.<\/p>\n Forests are especially effective at moderating temperature extremes during drier periods, improving local resilience to global warming. Reduced cloud coverage during dry spells increases solar radiation, causing trees to photosynthesize more and therefore pump more moisture from deep in the soil to the atmosphere, cooling the air.<\/p>\n Forest cover in the tropics<\/a> provides the greatest cooling benefits. The combined biophysical cooling effects of tropical forests<\/a> are so significant that, when combined with the effects of global emissions-related warming, their loss can\u00a0double\u00a0the local warming caused by global emissions alone. At the global scale, tropical forest loss<\/a> effectively\u00a0amplifies\u00a0the warming effects of deforestation-related emissions by about 50%.<\/p>\n Can Forest Restoration Also Restore Cooler Temperatures? One study found that reforestation and afforestation in the tropics and temperate regions from 2000-2010\u00a0reduced\u00a0the warming effects of deforestation by 0.2 degrees C (0.3 degrees F). Increasing tree cover in the boreal region had no effect, likely because snow-covered ground reflects more heat away from the earth\u2019s surface than a forest. Models show that\u00a0increasing\u00a0tree cover\u00a0in the\u00a0Sahel\u00a0could reduce local temperatures in some areas and increase them in others. In\u00a0urban heat islands\u00a0\u2014 areas of higher temperatures within\u00a0cities\u00a0\u2014 large trees planted<\/a> for shade can mitigate the most intense heat by shielding the sun and cooling via evapotranspiration.<\/p>\n Adding trees to agricultural landscapes (where ecologically appropriate) can also mitigate local temperature extremes and boost yields.\u00a0Livestock\u00a0are vulnerable to heat stress, which can negatively affect growth, meat and milk production, reproduction and disease. One study comparing\u00a0tropical savannas\u00a0where livestock grazing occurs found that the cooling benefits of trees increased linearly with the amount of carbon stored in trees: each additional 10 metric tons of carbon stored per hectare were associated with cooler local temperatures of 0.83 degrees C (1.5 degrees F) in Africa and 1.1 degrees C (2.0 degrees F) in the Americas.<\/p>\n While such findings do not prove that adding trees to degraded landscapes results in cooling, recent research based on historical data suggests that it can: Trees planted<\/a> during the 1930s\u00a0Great Plains Shelterbelt initiative, which spanned from Northern Texas to the U.S.-Canada border, lowered regional temperature averages by 1.7-2.1%, reduced the number of extreme heat days by 12.9%, and increased precipitation by 4.4-8.0%. Ultimately, these changes increased corn yields by 54.3% and influenced farmer decisions about which crops to grow.<\/p>\n In the tropics, there is evidence that increased temperatures due to tree cover loss can decrease crop yields, while adding trees to farms \u2014 a practice known as agroforestry \u2014 can protect<\/a> crops from heat stress. In\u00a0Brazil, land conversion and forest<\/a> losses from 1985-2021 decreased soy productivity by 6-12%, equivalent to lost profits of $158 per hectare. Meanwhile, agroforestry systems in Ethiopia\u00a0have been modeled\u00a0to increase national maize yields under future climate<\/a> conditions by 3.1 \u2013 7.5% compared to maize farms without trees.<\/p>\n These studies demonstrate that, in some cases, the addition of trees to agricultural landscapes can help crops and animals adapt to stresses brought on by greenhouse gas-induced climate change<\/a>. Scientists contributing to the Science Panel for the Amazon concluded that increasing forest<\/a> cover could provide additional benefits for society beyond agricultural producers by\u00a0mitigating higher temperatures.<\/p>\n Why Do the Answers to These Questions Matter? Higher temperatures pose extreme risks to\u00a0human health. One model showed that by 2100, conversion of the Brazilian Amazon to savanna could expose an additional 11 million people\u00a0to heat stress. In\u00a0Indonesia, a study demonstrated that worker productivity declined by over 8% in deforested areas due to reduced work quality and workers needing to operate more slowly and take more frequent breaks.<\/p>\n The biophysical effects of restored forests on local climate could add up to significant benefits for regional economies and food production. For example, of the 29\u00a0megacities\u00a0in the world, 19 depend on rainfall recycled from land for greater than a third of their water supply. The potential for trees in agricultural landscapes to buffer yields are additional to other forms of\u00a0agricultural adaptation\u00a0to climate change<\/a>, such as reducing soil erosion and providing pollinator habitat.<\/p>\n Mitigating the local impacts of global climate change<\/a> is especially important for communities that are most vulnerable to such changes, such as\u00a0Indigenous Peoples and local communities\u00a0who are dependent on forest-based goods and services for meeting their basic needs, and others dependent on rain-fed agriculture in the tropics. The non-carbon benefits of forests for climate<\/a> stability may be more immediately relevant to local, national and regional constituencies than forests\u2019 carbon benefits, due to their ability to help humans adapt to warmer climates with more extreme weather.<\/p>\n Yet there is still much left to be learned about the degree to which forest restoration can help restore the non-carbon benefits of forests, thereby buffering local communities and national economies<\/a> from the adverse effects of global greenhouse warming.<\/p>\n What Are the Opportunities to Learn More About Restoration\u2019s Benefits? To continue to build widespread support for forest restoration across scales, the international restoration community must fully understand and communicate restoration\u2019s full climate benefits. This includes the extent to which restored forests can regulate temperature and precipitation through non-carbon pathways, which is far less understood than the GHG effects of trees removing carbon from the atmosphere as they grow.<\/p>\n Importantly, incorporating non-carbon benefits into restoration planning could create new constituencies for forest<\/a> restoration. While local communities and officials may feel powerless to affect the trajectory of global climate change<\/a>, restoring forests and planting trees to stabilize local climates is something they can dig into. Research into this topic may give us answers that could help make a stronger case for restoration\u2019s role in fighting climate change.<\/p>\n Several key questions to be answered through research include:<\/p>\n Large-scale restoration landscapes such as those in Brazil\u2019s Atlantic Forest and the African Sahel, and afforestation initiatives such as China\u2019s<\/a> Green for Grain program, are coming into maturity and could be the basis of future studies that help us understand restoration\u2019s full impacts on climate. Advances in remote sensing<\/a> offer opportunities to explore these questions through empirical data. A portion of the energy<\/a> and finance behind ongoing international initiatives can and should be channeled into supporting critical research.<\/p>\n
\n<\/strong>While few studies have successfully measured the impacts of large-scale restoration on rainfall \u2014 and those that have been done have mostly focused on temperate latitude \u2014 emerging evidence shows that restoring degraded lands can improve precipitation.<\/p>\n
\n<\/strong>Forests in temperate and tropical latitudes reduce local temperatures by directly blocking sunlight from reaching the ground. Additionally, through evapotranspiration and by creating wind turbulence, forests move moisture and latent heat higher into the atmosphere, cooling the earth\u2019s surface and moderating local and regional temperature extremes.\u00a0Surface temperatures\u00a0in the tropics are on average .2 \u2013 2.4 degrees C (.4 \u2013 4.3 degrees F) cooler in forests than in nearby cleared areas, but temperature differences as high as 8.3 degrees C (14.9 degrees F) have been measured during the\u00a0hottest\u00a0part of the day.<\/p>\n![\"\"](\"https:\/\/files.wri.org\/d8\/s3fs-public\/styles\/1260_wide\/s3\/2022-10\/tropical_forests_cooling.png?VersionId=gguNl733TanzFZN8X_wG2JpqBOwuJ.zy&itok=s1U1Ud39\")
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\n<\/strong>An increasing body of evidence shows that restoring tree cover can reverse the effects of deforestation on local temperatures. However, that effect can vary, depending on the latitude at which the\u00a0deforestation\u00a0occurs, among other factors.<\/p>\n
\n<\/strong>The dynamic between forest restoration and local cooling and precipitation has critical implications for people\u2019s health, economies, agriculture and climate resilience.<\/p>\n
\n<\/strong>There currently is unprecedented international interest in forest restoration. Initiatives such as the\u00a0Bonn Challenge,\u00a0AFR100\u00a0and\u00a0Initiative 20\u00d720\u00a0have set continental- to global-scale targets for\u00a0ecosystem restoration<\/a>. The UN declared 2021\u20132030 the\u00a0UN Decade on Ecosystem Restoration<\/a>. At the One Planet Summit in 2021, financial institutions committed\u00a0$19.6 billion\u00a0to restore degraded land and forests in Africa. And most recently, the\u00a0Kunming-Montreal Global Biodiversity Framework<\/a>, agreed at the Conventional on Biological Diversity COP15 in December 2022,\u00a0set the global target\u00a0of placing 30% of degraded ecosystems under restoration by 2030.<\/p>\n\n