• Problem/issue being addressed
Global climate change, caused by increasing greenhouse gas emissions (e.g. CO2), is occurring at rates much faster than anticipated and its effects are clearly felt worldwide, which poses major challenges for the sustainable development of human society as a whole and particularly those in the developing countries like Africa. Global terrestrial vegetation is a major CO2 pool with large spatial and temporal variations, but also large uncertainties due to our lack of knowledge on the underlying interaction between vegetation and climate. The poor understanding of vegetation-climate interaction limits the projection of further climate change, thereby our action to it. The impacts are especially severe in Africa as people’s livelihoods are strongly dependent on local ecosystem services, such as grazing, agriculture, firewood, and construction timber. In addition, the rapidly increasing African human population and fast-changing socio-economic conditions put more pressure on existing ecosystem services. From the remote sensing sector, the new advances in passive microwave technology, for example, the Soil Moisture Ocean Salinity (SMOS) mission, provides new perspectives for monitoring vegetation changes compared to the traditionally used greenness-driven approaches. This project is addressing the issue of how to make use of the novel satellite passive microwave technology to improve our understanding of vegetation changes at global and continental scales, with particular focus on Africa.
• The importance of society
The United Nations has identified 17 key Sustainable Development Goals (SDGs), which are an urgent call for action by all countries. This project is directly related to two of the 17 SDGs, which are climate action and life on land. The results and insights gained on global vegetation are beneficial for 1) improving the modeling of vegetation-climate interaction and thus more accurately projecting future scenarios of climate change and 2) for protecting and sustainably managing the vegetation resources, with particular importance for Africa.
• Overall objectives
The overall objective of this project is to accurately quantify vegetation spatial and temporal changes in terms of water and carbon. Specific scientific questions answered are:
1. How does the global plant water storage vary over the season and how they related to the seasonality in the canopy greenness?
2. How has the phenology of vegetation water content and greenness changed, respectively, during the last decades in the tropics and what are the main drivers behind the phonological changes?
3. What are the main environmental drivers of vegetation phenology (particularly the dry season greening) in Africa?
• Conclusions
This project has produced 2 peer-reviewed papers on top journals, including Nature Ecology & Evolution and Remote Sensing of Environment and 1 manuscript, answering the questions listed above. The results highlight that 1) the African Miombo woodlands exhibit a unique behavior regarding the seasonal coupling of water and greenness (i.e. large time lag between the two), which is different from the boreal and temperate forests, 2) satellite passive microwave can contribute to reveal a full picture of the land surface phenological changes in the tropics, with about 25% more areas as compared to only using optical remote sensing, and 3) groundwater interannual variability was the major driver of dry season greening in the African dry tropics.
