27/03/2024
39 views
0 likes
When it comes to predicting what our climate will be like in the future, vegetation matters. Plants and trees exert a powerful influence over both the energy cycle and the water cycle. And, crucially, it is estimated that vegetation draws down well over three billion tonnes of carbon from the atmosphere each year – this is equivalent to a third of greenhouse-gas emissions from human activity.
Accounting for vegetation growth is clearly important in the complex climate puzzle – and the release of a new satellite dataset is set to help climate modellers with the challenge of evaluating the impacts of climate change.
Climate modellers rely on satellite data to assess the health and growth of the world’s vegetation. ESA’s Climate Change Initiative’s latest data release provides a consistent time series to meet modellers’ needs. This new dataset comprises information on Leaf Area Index (LAI), which describes the amount of leaf area in the canopy, and the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), which describes how much solar radiation is being absorbed by the leaves.
Both are key to describing the pattern and rate of vegetation growth and sit alongside 53 other recognised Essential Climate Variables that are used by science and policy circles to monitor the climate.
Spanning the years 2000–2020, the new dataset incorporates observations from multiple sensors such as those carried on the French SPOT series of satellites and ESA’s Proba-V mission.
The dataset is available at 1 km grid resolution over five-day intervals – sufficient for use in global carbon and climate models. Critically, the dataset provides full uncertainty estimates, in other words – a measure of confidence, and traceable validation using global in-situ measurements.
“Climate modellers place great emphasis on the quality of the input data they use. The more precisely they can quantify the accuracy of this information, the more confidence they can have in their forward-looking projections,” explains Christiaan van der Tol of Twente University in the Netherlands and science leader of the Climate Change Initiative Vegetation Parameters project.
This first version of the dataset covers a north–south transect from Finland to South Africa. It provides an opportunity for users to familiarise themselves with the data and features in preparation of switching to a global product, which is the next step in the project’s development effort.
The images in the slider above show the difference in FAPAR over western Europe between July 2010 and July 2018.
The images in the slider below show the difference in LAI over part of central Africa for the same periods.
Dr van der Tol adds, “We have satisfied the target requirements defined by the Global Climate Observing System in this first release and provide a five-day time step compared to the eight-to-10-day time of existing datasets.
“Now, we are working to extend the data globally and incorporating observations from additional sensors such as the Ocean Land Colour Instrument carried on Copernicus Sentinel-3 and the Advanced Very-High Resolution Radiometers carried on the family of US Polar-orbiting Operational Environmental Satellites and Europe’s MetOp satellites.”
ESA’s Clement Albergel noted, “In a third development cycle we will also focus on a feasibility study to include solar-induced chlorophyll fluorescence products such as from ESA’s FLEX Earth Explorer mission when it is in orbit, which will provide valuable information on vegetation stress.”
The current phase of the project runs to the end of 2026 with algorithm and processing systems sufficiently mature that the global product could be used and extended in an operational context.
The current version also has some interesting experimental features. The data are unsmoothed, so while being ‘noisier’ than some other datasets, this may be useful to detect and investigate sudden events, such as disturbance from fire or harvest.
The dataset is produced by the ESA Climate Change Initiative’s Vegetation Parameters project, one of 27 R&D projects dedicated to developing robust satellite climate data records that provide the observed evidence to understand the climate and underpin the tools and decisions used to tackle the negative consequences of a changing climate.