Trends in surface moisture conditions of European peatlands in the last decades - a remote sensing approach

Representing the Earth’s most efficient terrestrial carbon store, intact peatlands play a key role in climate change mitigation strategies and provide multiple other ecosystem services such as flood prevention and refugia for rare species. The carbon sink function of peatlands is yet highly dependent on water saturation and vegetation composition. Nevertheless, drainage and peat extraction during the past centuries until today led to intense peatland degradation and turned more than half of all European peat soils and more than 90 percent of peat soils in Germany into a carbon source. Efforts have been increasingly made since the 1990s to restore peatlands, mainly by rewetting to recover peatland typical hydrological conditions. However, there is a lack of knowledge on restoration success for numerous sites, due to difficulties in funding long-term hydrological monitoring. Satellite remote sensing is an excellent method to address this deficiency, as it provides spatially continuous and temporally highly resolved information on the environment, including peatlands.

Making use of freely available data of the Landsat Mission, this study aims to analyze trends in surface moisture conditions of European peatlands over the last decades, a time frame in which many restoration measures have been implemented. We performed a pixel-wise trend analysis for European peatlands using the Normalized Difference Moisture Index as moisture indicator based on image time-series reaching back to 1984 and a spatial resolution of 30 x 30 m. Trend statistics using Mann-Kendall’s tau and Sen’s slope were calculated for each month separately to also enable analysis of changes in specific seasons, such as the growing season or shoulder seasons important for water recharge of the sites. Based on a random sample of peatland sites across all Europe, we show first results of european-wide trend patterns. For small-scale visualization and to facilitate a spatially explicit long-term monitoring of peatlands in active restoration management, we further present an open-source Google-Earth-Engine (GEE) application which additionally provides insights into changes in vegetation, as represented by the Normalized Difference Vegetation Index. 

Besides allowing the interpretation of changes in surface moisture conditions over the past decades, the GEE tool can also be used in the future to assess potential restoration sites or to improve our understanding concerning the resilience of peatlands in scenarios of a warming climate, where research is still in its infancy. The continental coverage of the analysis in combination with a temporal coverage of several decades on a monthly resolution offers exceptional possibilities for spatial planning and evaluation of European peatland restoration and can therefore contribute to a cost-effective implementation of climate change mitigation measures.