Beyond ‘greening’ and ‘browning’: trends in grassland ground cover fractions across Eurasia that account for spatial and temporal autocorrelation
Data files
May 15, 2023 version files 1.26 GB
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Lewinska_etal_2023_GCB_Dataset.7z
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README.md
Abstract
Grassland ecosystems cover up to 40% of the global land area and provide many ecosystem services directly supporting the livelihoods of over 1 billion people. Monitoring long‑term changes in grasslands is crucial for food security, biodiversity conservation, achieving Land Degradation Neutrality goals, and modelling the global carbon budget. Although long-term grassland monitoring using remote sensing is extensive, it is typically based on a single vegetation index and does not account for temporal and spatial autocorrelation, which means that some trends are falsely identified while others are missed. Our goal was to analyze trends in grasslands in Eurasia, the largest continuous grassland ecosystems on Earth. To do so, we calculated Cumulative Endmember Fractions (annual sums of monthly ground cover fractions) derived from MODIS 2002–2020 time series and applied a new statistical approach PARTS that explicitly accounts for temporal and spatial autocorrelation in trends. We examined trends in green vegetation, non-photosynthetic vegetation, and soil ground cover fractions considering their independent change trajectories and relations among fractions over time. We derived temporally-uncorrelated pixel-based trend maps and statistically tested whether observed trends could be explained by elevation, land cover, SPEI3, climate, country, and their combinations, all while accounting for spatial autocorrelation. We found no statistical evidence for a decrease in vegetation cover in grasslands in Eurasia. Instead, there was a significant map-level increase in non‑photosynthetic vegetation across the region and local increases in green vegetation with a concomitant decrease in soil fraction. Independent environmental variables affected trends significantly, but effects varied by region. Overall, our analyses show in a statistically robust manner that Eurasian grasslands have changed considerably over the past two decades. Our approach enhances remote‑sensing‑based monitoring of trends in grasslands so that underlying processes can be discerned.
Methods
Complete methodology description available in the paper featuring the data: (Lewinska et al. 2023).
Usage notes
The complete dataset comprises six GeoTIFF files in ZSTD compression with three bands each describing 2002-2020 trends in grassland ground cover fractions:
[1] AR trend,
[2] P-value of the AR trend,
[3] strength of temporal autocorrelation.
Scale factor for each band is 10000
- GV: 2002-2020 trends in green vegetation ground cover fraction
- NPV: 2002-2020 trends in non-photosynthetic vegetation ground cover fraction
- SOIL: 2002-2020 trends in soil ground cover fraction
- GV_over_NPV: 2002-2020 trends in a ratio of green vegetation ground cover fraction over non-photosynthetic vegetation fraction
- GV_over_SOIL: 2002-2020 trends in a ratio of green vegetation ground cover fraction over a soil fraction
- GVNPV_over_SOIL: 2002-2020 trends in a ratio of a sum of green vegetation and non-photosynthetic vegetation fractions over soil ground cover fraction
`METADATA:
Driver: GTiff/GeoTIFF (ZSTD compression)
Size is 22596, 5101
Coordinate System is:
GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433],
AUTHORITY["EPSG","4326"]]
Origin = (26.239789449000000,57.065478423000002)
Pixel Size = (0.004491576420605,-0.004491576420506)
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
COMPRESSION=ZSTD
INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left ( 26.2397894, 57.0654784) ( 26d14'23.24"E, 57d 3'55.72"N)
Lower Left ( 26.2397894, 34.1539471) ( 26d14'23.24"E, 34d 9'14.21"N)
Upper Right ( 127.7314502, 57.0654784) (127d43'53.22"E, 57d 3'55.72"N)
Lower Right ( 127.7314502, 34.1539471) (127d43'53.22"E, 34d 9'14.21"N)
Center ( 76.9856198, 45.6097128) ( 76d59' 8.23"E, 45d36'34.97"N)