- A new study shows concerning links between deforestation and reduced precipitation in tropical regions, which can in turn lead to reduced agricultural yields and food security issues.
- Now, researchers are concerned about the potential for another El Niño, which typically brings hotter, drier conditions to tropical regions, particularly in Southeast Asia, and can compound the effects of deforestation and reduced rainfall.
- The 2015-16 El Niño triggered crop losses, disease outbreaks, malnutrition and food insecurity, livestock deaths and other hardships that affected 60 million people globally; researchers say these trends signal the need for greater climate resilience in local communities.
It’s been seven years since the last significant El Niño — one of the strongest on record. It triggered disease outbreaks, caused changes in weather conditions that affected fisheries and agricultural production, killed livestock and led to malnutrition and food insecurity. This extreme phenomenon affected more than 60 million people across the globe. And now, climate scientists say, we’re potentially on the cusp of another El Niño. What’s more, new research shows that these El Niño effects could be coupled with another phenomenon happening simultaneously: the reduction of precipitation due to forest loss, which can have profound impacts on agriculture.
This is particularly concerning In Southeast Asian countries where deforestation has been accelerating rapidly in recent years to support agriculture and food production, particularly in Indonesia, where the most rampant deforestation in the region has been recorded. Meanwhile, in 2016, extreme temperatures in Southeast Asia caused by El Niño resulted in peak energy consumption, disrupted crop production and caused severe human discomfort, a 2017 study notes. And now, researchers and aid workers alike are bracing for the coming months of potentially damaging weather.
In the recent study, published in the journal Nature in March, researchers from the University of Leeds in the U.K. analyzed the impact of forest loss on rainfall using satellite data sets of forest cover change from 2003 to 2017, with a focus on forests of the Amazon, Congo and Southeast Asia. They found that the effect of deforestation on precipitation intensified at scales larger than 50 kilometers (31 miles), with the greatest decline in precipitation occurring at 200 km (124 mi), which is the largest scale explored by the study.
Callum Smith, the lead study author, notes that different things happen at different scales of forest loss. At small scales, the researchers think forest loss could actually contribute to an increase in precipitation. He says when forests are chopped down, the land becomes warmer and reflects more heat so it can drive cloud formations, pushing moist air upward and forming clouds. However, at large scales, there is a reduction in rainfall. The researchers point to reduction in evapotranspiration, the process of water evaporating from the soil and transpiring from a plant’s body, as the main driver of this decrease in precipitation.
“Trees transpire and evaporate moisture from their leaves. It pumps up moisture into the air. And when that moisture source is lost, you get reduction in the formation of clouds above these larger forests,” Smith says.
According to Smith, other studies have found that forest loss can exacerbate the impacts of El Niño through reduced precipitation. Included in their analysis period is the 2015-16 El Niño, in which they found a stronger reduction in rainfall over regions with forest loss in the Amazon and Southeast Asia.
“We [found] a small potential link between El Niño and reduced precipitation due to forest loss,” Smith says. “We also note that precipitation is particularly sensitive in drought years, when there is less background moisture available in the atmosphere.”
Broadly speaking, El Niño years bring warm and dry conditions to the Amazon and Southeast Asia. “This drying can act to increase the amount of water that plants and trees ‘breathe’ out or transpire,” Smith says. “This is broadly due to increased evaporative demand — the plants need more moisture to evaporate from their leaves to maintain their cool environment when the background temperatures increase. So we hypothesize that decreases [in rainfall] in the El Nino years are slightly stronger because of this ‘missing’ inflated effect.”
According to the study, the higher transpiration rates observed in tropical forests during those El Niño years is one probable reason for the strong precipitation response to forest loss in regions and periods impacted by El Niño.
Wilhelmina Pelegrina, Greenpeace Southeast Asia’s regional campaigner for ecological agriculture, says that deforestation-induced precipitation reduction coupled with El Niño will possibly lead to more forest fires, pronounced transboundary haze, crop failures and negative social impacts such as indebtedness, school dropouts and health impacts.
“We have seen this in 2015, where peat forests were engulfed with fires, destroying habitats and affecting the health, livelihoods and homes of communities,” Pelegrina says.
She also mentions that with reduced precipitation, crop growth and harvests will be affected due to expected longer dry months. In the 2015-16 El Niño in the Philippines, her organization produced a documentary on how Filipino farmers were coping.
“We have documented and [bore] witness to community stories on impacts of El Nino — maize farmers and Indigenous communities thrown into a cycle of indebtedness as they cannot recover from crop losses, season after season. Along with the drought, they also experienced rat infestation, which decimated their crops,” she says.
According to Pelegrina, her organization was also able to talk to communities that had to move from their ancestral lands to cities — living in temporary shacks while trying to find work — to secure their food and water needs. This resulted in children being forced to stop school to help find work because it was simply not practical to send them to school; there was no water for them to drink, cook food and prepare them for school, she says.
In northern Thailand, they were also able to hear stories of farmers and community conflicts over water, drying river waters and losses on fruit farms or orchards and rice farms.
Reduction in agricultural yield
Smith says that the study’s findings on the changes in precipitation in the tropics won’t necessarily mirror what happens globally — but the effects will be felt worldwide, nonetheless. “So we can’t say there’ll be a [precipitation] reduction globally. But what we can say is this reduction will impact people living all around the world,” Smith says.
According to him, if forests are lost, rainfall in the area will reduce and will consequently mean reduced agricultural yield. “In most parts of the world, we depend on food that originates from the tropics. And if yields decline, then there’ll be less food available [for] the global community.”
As the study notes, reduction in precipitation induced by forest loss has important implications for society. For every percentage point reduction in rainfall, there is a 0.5% reduction in crop yields, and those forest loss-induced changes to annual precipitation could result in crop yield declines of 1.25% for each 10% loss of forest cover.
“If forests are lost, then rainfall in the area will reduce. And that means that agriculture yields will decrease because agriculture needs water. And if there’s less [water], the land will be less productive,” says Smith.
Moreover, Smith also mentions a possible compounding effect: “Because there’s a reduction in rainfall and the agriculture yields decline, more land is then deforested [for] agriculture to make up for the lost yield.”
Amelia Henry, senior scientist II from the International Rice Research Institute (IRRI), says reduced precipitation will cause reduced yield in rainfed agricultural systems. The U.N.’s World Water Development Report 2021 says that rainfed agriculture covers 80% of the world’s croplands and accounts for 60% of food production. “Rainfed farmers are the most vulnerable to drought because they have no option of irrigating, and their decisions on when and what to plant have a huge effect on their crop yield,” Henry says.
Moreover, Pelegrina says this reduction in crop yields is a threat to Southeast Asia’s food security and for crop-exporting countries, even a threat to livelihoods and local economies. According to her, a combination of El Niño and less precipitation spells less volume of rice produced, which will have implications for import-dependent countries such as the Philippines.
“In the past, we have documented how rice farmers in the Philippines suffered from El Nino and long dry spell — they had crop losses, their livelihoods were negatively impacted, even their own source of food. Depending on the intensity of El Nino, we’ve [witnessed] some farming families enduring hunger and loss of income,” she says in an email.
According to a 2017 U.N. report on climate resilience in Asia and the Pacific, the 2015-16 El Niño took its heaviest toll on food security and agriculture, destroying crops, killing livestock and drying up water sources in parts of Asia and the Pacific.
“The background climate conditions that El Nino produces are drying and warming in the Amazon and Southeast Asia. This could depress crops that are currently moisture limited, as there will be less rainfall in general in the coming El Nino period,” Smith writes in an email. “This is on top of the background climate change signal, which is also trending to warmer and drier, but with more extremes in temperature and precipitation. Conversely, crops that are limited by temperature could increase productivity in El Nino periods.”
The need to push for tropical forest conservation
The research by Smith and his colleagues demonstrates the need for tropical forest conservation to support climate resilience.
Smith says their study “highlights the impact of keeping forests for people that live there [because] if these forests remain, people who live there will benefit because the rainfall won’t be reduced.”
He adds that it is also important for policymakers in Brazil, Central African countries and Indonesia, for example, to put in place strict legislation to reduce forest loss so “the people who live in these countries have livelihoods that they can earn from [because] decreasing rainfall in those areas means they’re less likely to be able to make money from the land and live there.”
To address and combat the possible effects of reduced precipitation as well as the oncoming El Niño on agriculture and food security, Pelegrina calls on governments to channel resources to community innovations that address deforestation and climate change impacts, on communities to innovate and implement on-the-ground solutions, and on civil society groups to ensure that community voices are heard and are part of decision-making processes related to forest resources, food and agriculture.
Additionally, Pelegrina says Southeast Asian leaders must unite to end deforestation. “Act on illegal oil palm expansion in forests, make the corporations violating regulations and continually into deforestation held accountable and ordered to pay up for the different layers of damages brought to communities by their continued deforestation,” she says.
“Protecting our forests is clearly important for resilience not only to drought but also excessive rain, as we see here in the Philippines in terms of landslide and flooding risk,” says Henry of IRRI. “In terms of agriculture, we need to support research that develops new stress-tolerant varieties and especially the dissemination of seed of the new varieties to farmers who need them. Availability of those varieties will improve the climate resilience of rainfed farmers.”
Smith, C., Baker, J.C.A. & Spracklen, D.V. Tropical deforestation causes large reductions in observed precipitation. Nature 615, 270–275 (2023). https://doi.org/10.1038/s41586-022-05690-1
Thirumalai, K., DiNezio, P., Okumura, Y. et al. Extreme temperatures in Southeast Asia caused by El Niño and worsened by global warming. Nat Commun 8, 15531 (2017). https://doi.org/10.1038/ncomms15531
UNESCO World Water Assessment Programme. (2021). The United Nations world water development report: Valuing water. UNESCO Publishing.
Enhancing Resilience to Extreme Climate Events: Lessons from the 2015-2016 El Niño Event in Asia and the Pacific. (2017). Retrieved from UNDP website: https://www.unescap.org/sites/default/files/El%20Nino%20report-%20finalized%20ESCAP07082017.pdf