Impacts of the Congo basin deforestation on the African monsoon patterns

The Congo Basin is located in Central Africa spanning across six countries. It is one of the three main rainforests worldwide and plays a key role in regulating monsoon patterns across much of Africa. There are about 10,000 species of tropical plants in the Congo Basin and approximately 30% are endemic to the area. Additionally many endangered animals call the Congo home from mountain gorilla, chimpanzees and forest elephants. The Congo rainforest has been inhabited by humans for over 50,000 years and is key to providing them with shelter, food and freshwater. Increasing rates of deforestation is threatening this fragile ecosystem and not only is the biodiversity within under threat, but the entire hydrological cycle of Africa as well. 

Picture courtesy of: Planet.com representing the Congo Basin in green

The Congo basin is highly dependent on precipitation as there are few low intensity aquifers in the region to sustain farming and human activity. Much of the economic activities relies on rain-fed agriculture and hydroelectric power and thus, makes this region vulnerable to climate change. The Congo Basin has two annual rainy season following the passage of the Intertropical Convergence Zone. March to May and September to November mark the months with the most precipitation while June-August are the driest months. Deforestation has drastic impacts on these rainfall patterns and this blog post is going to explore how. 

Nogherotto et al, 2013 investigated the relationship between land cover change in Central Africa due to deforestation and the African monsoon patterns. According to the UN Food and Agriculture Organization (FAO), Central Africa had an annual deforestation rate of 0.23% between 2000-2010. However, an increased to 0.3-0.5% is expected by 2020-2030. Deforestation causes an increase of land surface albedo, a decrease in surface roughness and a shift in the evapotranspiration of the surface. These changes in surface properties have been predicted to not only have an effect on local climate but also global patterns as the tropical areas of Africa have been recognised as a global region where land surface conditions have a greater impact on regional climate. Generally, increasing deforestation has been linked to a decrease in precipitation and an increase in temperature over the deforested area. Deforestation of the Congo may have a greater impact through the shift of monsoon patterns across Africa, which would be detrimental to communities who rely on rainwater as their freshwater source. 

Compared to tropical forest, short grass growth following deforestation has a lower leaf area index, lower roughness and higher albedo. Additionally, the relationship between soil moisture and evaporation changes as a result of deforestation. Both soil moisture and evapotranspiration decrease and deforested regions face a greater challenge of extracting and using soil moisture than forested areas. The ratio of evapotranspiration over soil moisture in the root zone was calculated and the results found a 7.7% decrease in the ratio in the dry season and a 4.5% decrease during the October-February monsoon. This suggests that communities in deforested regions will be prone to additional water stress as a result of the decreasing ability to extract water from the soil. 

Figure 2 below shows up to 50% reduction in the precipitation of the deforested area (panel c&d) that can be correlated to a surface increase of up to 4°C over the same area (Figure 3). However, deforestation not only has local drying impacts over the Congo Basin but also remote effects on precipitation patterns in other areas of Africa. 

Figure 2: Panels a&b showing mean precipitation (mm) for the June-September season (a) and October-February (b) with the deforested area highlighted in red 

  Panels c&d showing precipitation difference (%) for June-September (c) and October-February (d)

Image courtesy of Nogherotto et al, 2013

Figure 2: Change in surface temperature (degree C) between 200-2007 for June-September season (a) and October-February (b) 

Image courtesy of Nogherotto et al, 2013

In figure 2 and 3, it can be observed that there is an increase in precipitation In the Sahel Desert extending up towards Ethiopia between June-August with a shift in surface temperature. Between October and February in the Namibian desert and across much of Southern Africa, there is a significant increase in precipitation with a drop in surface temperature. Furthermore, there is evidence that in June-August, the West African monsoon intensifies and causes a Northerly shift in the monsoon rain bands resulting in an increase in precipitation over the Sahel and decrease over the Guinea coast. In December-February, the South-Equatorial African monsoon strengthens causing a significant increase in precipitation over Southern Africa. Thus, deforestation in the Congo Basin not only results in a local shift of evapotranspiration and soil moisture levels but has the capability of shifting entire monsoon patterns across the African continent. 

If deforestation continues at this rate, the hydrological patterns across Africa could face drastic changes and have detrimental effects on communities who rely on stable rainfall patterns for freshwater. This study was one of the firsts of its kind and despite being a few years old, it has made it clear that African monsoon patterns are directly correlated to anthropogenic pressure from deforestation and land-use change. Thus, it is important to understand the link between the Congo Basin the rest of Africa to reduce the impacts of deforestation on freshwater access for African communities.