Deforestation may hurt U.S. agriculture, affect monsoon cycle

Unchecked deforestation will have far-reaching impacts on temperature, rainfall, and monsoon cycles in regions well outside the tropics, affecting agriculture and water availability, warns a new report published by Greenpeace International.

The report, titled An Impending Storm: Impacts of deforestation on weather patterns and agriculture, is a synthesis of dozens of recent scientific papers that assess the effects of forest cover loss on weather patterns, local climate, and agricultural productivity.

While noting that there remains a great deal of uncertainty on how deforestation affects weather and climate, the report says “many models show wide scientific consensus that deforestation has the potential to disrupt weather and climate systems on a local, regional and global scale.”

Transpiration above the rainforest canopy in Malaysian Borneo

An Impending Storm cites examples from the Amazon, West Africa, Southeast Asia, and the world’s boreal forests.

“Modeling suggests that loss of forests in areas such as Amazonia and Central Africa can severely reduce rainfall in the US Midwest at times when water is crucial for agricultural productivity in these regions,” states the report, which goes on to summarize several potential indirect impacts of deforestation at regional scales, including worsened air pollution, reduced coastal production, increased temperatures, and altered monsoon cycles.

Rainforest in Malaysian Borneo

Greenpeace concludes with a call to embrace the precautionary principle by protecting forests and the services they afford humanity.

“Employing the precautionary principle and conserving existing forest ecosystems under a ‘Zero Deforestation’ footprint is the only way to ensure that forests continue to regulate our weather and climate, minimize the indirect effects of deforestation and conserve biodiversity.”

Predicted impacts of deforestation on weather patterns and crop yields around the world: results from computer modeling studies (Figure from the Greenpeace report).

Summary of potential regional impacts of deforestation from the Greenpeace report
Excerpted from the report

Indirect impacts of Asian deforestation

Rainfall: Southeast Asia is modeled to have a 1mm/day decrease in rainfall throughout
the year if forest cover loss is complete (Werth & Avissar, 2005a), with southern China
and Vietnam undergoing a 20-30% decrease in rainfall (Sen et al., 2010).
Temperature: Models indicate a regional increase in air temperature of 1°C after complete
deforestation (Schneck & Mosbrugger, 2011).
Monsoons: It was suggested that the East Asian monsoon flow would weaken over
eastern China and the South China Sea, but become enhanced over mainland
Southeast Asia after complete deforestation (Sen et al., 2004; Sen et al., 2010).
Oceans: Surface temperatures could reduce by up to 1.25°C in the Southern and
South Indian Oceans, but increase by 0.75°C in the South Pacific Ocean after complete
deforestation, impacting ocean circulation (Schneck & Mosbrugger, 2011).
Coastal protection: Removal of mangrove forests increases community exposure to ocean
and tidal influences such as cyclones and tsunamis (Kathiresan & Rajendran, 2005)
Human health: Smoke from fires associated with deforestation, particularly of peat
forests, adds considerably to existing urban air pollution in Southeast Asia, especially in
El Niño years (Johnston et al., 2012; Marlier et al., 2013). This can affect people’s health,
not only in the immediate vicinity, but also in urban centers near forest burning.
Teleconnections: A 20-25% decrease in rainfall in western Turkey (Avissar & Werth,
2005), enhanced storm track activity over Scandinavia (Snyder, 2010), changes to
European storm track locations (Snyder, 2010), cooling in Siberia of 1°C, and increased
temperatures in Canada and central Africa, are all suggested as consequences of
complete Asian deforestation (Schneck & Mosbrugger, 2011).

Indirect impacts of African deforestation

Rainfall: Modeling suggests widespread reductions in rainfall of 1mm/day locally (Werth
& Avissar, 2005b), with a 2-3mm/day decrease in the dry season (Semazzi & Song, 2001)
after complete tropical African deforestation. These models showed regional patterns;
Mozambique would experience reduced rainfall, while Botswana, Zambia and the
southern Democratic Republic of Congo would experience increased rainfall.
Temperature: Land surface temperatures were indicated to increase locally between 1.2-
2.4°C following complete deforestation of South Sudan (Salih et al., 2012).
Monsoons: The West African monsoon weakens due to reduced northward moisture
transport after modeled loss of West African forests (Abiodun et al., 2008).
Agriculture: Western Kenyan agriculture production was expected to reduce following
decreased rainfall linked to local forest loss (Otieno & Anyah, 2012).
Teleconnections: Models of complete forest loss in central Africa suggest a 5-35% rainfall
decrease in the US midwest (Avissar & Werth, 2005), which could impact crop harvests
and global food supply. The Arabian Peninsula was expected to have a 15-30% increase
in rainfall (Avissar & Werth, 2005).

Indirect impacts of Amazon deforestation

Rainfall: Annual rainfall is modeled to decrease by 10-20% across the entire basin after
total Amazon deforestation (Moore et al., 2007), but there are some regional differences.
The northwest of the basin is predicted to become drier by up to 2mm/day, while the
southeast may become wetter by up to 1.5mm/day (Medvigy et al., 2011).
Flood risk: Annual discharges into a river in the southeast of the Amazon have increased
by 25% following land use change (forests to agriculture) over the past 40 years (Costa et
al., 2003), and flood risks are considered to have increased (Davidson et al., 2012).
Temperature: Modeling complete conversion of Amazonian forest to agriculture
suggests significant temperature increases locally of around 2°C (Feddema et al., 2005).
The frequency of extreme cold events is indicated to triple in the south and west of South
America, which would impact agriculture (Medvigy et al., 2012).
Agriculture: Reductions in rainfall and increased extreme cold events would negatively
impact crops such as coffee, maize, soybean and wheat (Medvigy et al., 2012).
Teleconnections: With complete deforestation of the Amazon, rainfall is suggested to
decrease by 25% in Texas, but increase by 45% in the Arabian Peninsula (Avissar &
Werth, 2005). At the same time, Northern Europe would also experience increased
annual rainfall (Feddema et al., 2005).