Beyond carbon storage: the Congo Basin forest as rainmaker
文 / Denis Sonwa (世界森林研究中心, Center for International Forestry Research, CIFOR)
譯 / 人禾環境倫理發展基金會
氣候變遷的因應，常常會被分成兩個主要議題：減量(減少溫室氣體排放)與適應(調整生計跟生活方式來影響氣候變遷)。其中適應的策略包括，以生態系為基礎的調適(ecosystem-based adaptation, EBA)，這是一個透過對利用自然資源跟生物多樣性的促進，來協助脆弱的社區發展適應性策略的途徑。在這樣的考量下，剛果盆地的森林在關於調節降雨的研究中，扮演著有亮眼的角色。
Responses to climate change are grouped into two main categories: mitigation (reducing greenhouse gas emissions responsible for climate change) and adaptation (adjusting livelihoods and life styles due to the influences of climate change). Amongst adaptation strategies, ecosystem-based adaptation (EBA) is an approach that promotes ways to use natural resources and biodiversity to help develop adaptation strategies for vulnerable communities. In this context, recent studies highlight the role that the Congo Basin forests play in generating rainfall, both regionally and in the continent as a whole.
Rainfall in an ecosystem originates from three main sources: moisture that is already in the atmosphere, moisture from outside the region, and evapotranspiration from surfaces within the ecosystem (forests and other land uses). Pokam et al. studied how the climate of the Congo Basin is primarily a result of moisture from the Atlantic Ocean and the recycling process of evapotranspiration. Previous studies had established that tropical forests such as the Congo Basin can evaporate up to 1 to 2 meters of water per year. In addition, research by Makarieva et al. suggests that forest cover in the region acts like a pump, moving oceanic moisture towards the continent to eventually become rainfall in that region.
With this role of forests as rainmakers in mind, Nogherotto et al. explored the impacts of deforestation in the Congo Basin on regional hydrological cycles, including the effects on the African monsoon. They modeled scenarios where the Congo Basin is forested versus those in which it is deforested (that is, modeling a situation where forest cover is transformed to short grass cover). Their findings indicate that deforestation in the Congo Basin would lead to modifications in rain behavior in the Sahel and over southern equatorial Africa.
Taken together, these three studies show how the Congo Basin acts as a mechanism for pumping water from the Atlantic Ocean, from underground sources, and from the soil. These sources then mix with atmospheric water, leading to the generation of rainfall both locally and on a sub-continental scale. Without the extensive forests of the Congo Basin, this process would be severely disrupted. In addition, these studies help highlight other important functions of the Congo Basin forests beyond biodiversity conservation and climate change mitigation.
With the growing scientific evidence of the multiple roles that the Congo Basin forests play at regional, continental and global scales, the case for forest conservation, for good forest management, and for multiple income streams to support the forests’ multiple roles becomes stronger. Given their rainmaker role, sustaining the Congo Basin forests might be one of the foundations for EBA to climate change for much of Africa.