‘Rainbow water’ – new evidence on the impacts of land evaporation on regional climate

During the UNFCCC technical meeting in Bon, Germany, ASB Partnership and World Agroforestry Centre (ICRAF) scientists organized a side event held in Zentrum für Entwicklungsforschung (ZEF), University of Bonn where they introduced a new dimension to evidence on climate change science known as ‘rainbow water’. This is actually an acronym that stands for Recycled Atmospheric Inputs Now Benefitting Our Water Supply.

Land evaporation has significant impacts on regional climate patternsLand evaporation has significant impacts on regional climate patternsThe concept of rainbow water, the scientists explain, is an approach to identify the effects and influence of trees and forests on ‘the rainfall, temperature, humidity and windspeed in which humans, crops and livestock live (the ‘micro-climate’) and on the landscape and regional patterns of rainfall (‘meso-climate’)’.

The scientists argue that the focus of international discussions has been on climate change effects on macro-level climate aspects that focus on carbon emission reduction and that the impact at micro-climate and meso-climate levels have largely been ignored. The ‘rainbow water’ concept helps to bridge this gap by identifying regional land use and land use change activities as having a major impact on these lower climate levels.

“Studies on which the rainbow water dimension is derived indicate that a high percentage of rainfall (40%) over land in one region originates from land moisture evaporation from another region. For example, maps depicting atmospheric moisture transport suggest that virtually most water transpired by trees in East Africa will come back as rainfall in West Africa,” explains Meine vanNoordwijk, Chief Scientist at ICRAF.

As such, activities on land use and land use changes in East Africa should be of interest to their counterparts in West Africa because they have a significant impact on the latter’s rainfall patterns.  If East Africa for example experiences a high deforestation rate, it means less moisture from land and in turn, less rainfall for West Africa -especially in the Congo Basin, which in turn supplies moisture for rainfall to the Sahel region. The same applies to China where a significant percentage of its water resources come from moisture evaporated from the Eurasian continent.  

According to Dr. Peter Minang’ ASB Global Coordinator, these new insights on regional level dynamics of rainbow water come with potential implications for current climate policy including moving away from ‘carbon centric’ land use discussions in the UNFCCC to a more balanced discussion recognizing the need for synergies between mitigation and adaptation, given that rainbow water is neither completely mitigation nor adaptation.

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