Climate change is rapidly altering the world's ecosystems, causing extreme weather conditions, such as droughts, to become increasingly frequent. Understanding the factors that contribute to ecosystem resilience to extreme events is vital to develop more effective strategies for climate adaptation and mitigation.

New research using data from ESA’s Soil Moisture and Ocean Salinity (SMOS) mission has provided some insights into how this can be achieved.

The contribution of space to climate action is being showcased this week as the Earth observation community gather at the first Global Space Conference on Climate Change (GLOC) by IAF.

GLOC 2023 is being held between 23 – 25 May in Oslo and aims to contribute to the global efforts to better understand and battle climate change, through the use of space-based services and applications.

The SMOS study is one such example of how remote sensing data empowers climate change research. The study, recently presented at EGU 2023, found that the way land is managed can influence ecosystems’ ability to resist the effects of drought and heat [1].

Researchers analysed global vegetation spanning from 2010 to 2020, using different satellite data, namely SMOS L-band Vegetation Optical Depth (L-VOD) as well as NASA MODIS kernel Normalized Difference Vegetation Index (kNDVI) and Enhanced Vegetation Index (EVI). The estimates of ecosystem resistance were then compared among them.

This comparison allowed the scientists to evaluate the advantages and limitations of each vegetation proxy and to better understand the relationship between vegetation structure, biomass, and ecosystem resilience [1].

The SMOS mission – launched in 2009 – uses a microwave L-band sensor to measure soil moisture levels. By analysing variations in Earth's radiation, it provides highly accurate information essential for understanding how ecosystems respond to stress events.

One of the key results of the study was that, for all three satellite datasets, ecosystems with higher forest cover show stronger resistance to droughts than cropland. However, only SMOS L-VOD detected that primary forests – forests undisturbed by humans – tend to be more resistant to these events than secondary ones.

Chenwei Xiao, doctoral researcher at the Max Plank Institute for Biogeochemistry and lead author of the study, said “Some studies reveal that SMOS’s L band VOD is better at penetrating the dense canopy of the forest compared to other VOD products. As a result, L-VOD better correlates with forest fraction and biomass.”

SMOS L-VOD’s accuracy has been documented before, demonstrating that the satellite is more sensitive to changes in forest biomass than other vegetation indices in temperate and tropical forests [2].

The study also suggests that old-growth trees in tropical evergreen broadleaf forests tend to be more drought-resistant than younger forests.

These findings suggest that SMOS data can be a valuable tool to help researchers better monitor ecosystems under climate change and assess the impact of land management alternatives.

For instance, the study shows that irrigation in water-limited regions can substantially improve the drought resistance of croplands.

Xiao added, “Humans have an effect on forest composition and structure through management, and we can detect its impact on forest resilience from satellites. This improved detection capacity has important implications for future ecosystem monitoring and management of the likely occurrence of extreme events”.

Learn more about SMOS Level-1 and Level-2 science data in this infographic.

References

1. Xiao et al., (Preprint) “Land-cover and management modulation of ecosystem resistance to drought stress.” EGUsphere. https://doi.org/10.5194/egusphere-2023-304.
2. Fan et al., (2019) “Satellite-observed pantropical carbon dynamics.” Nat. Plants. 5, 944–951.