Long-term global vegetation and climate index datasets

NDVI Data Set (1. NDVI.nc)

• Global Vegetation Greenness (NDVI) from AVHRR GIMMS-3G+, 1981-2022
• Variable: Normalized Difference Vegetation Index (NDVI)
• Area: Global (60°S ~ 70°N, -180°W ~ 180°E)
• Period: 1982-01-01 ~ 2022-12-31
• Horizontal resolution: 0.25° × 0.25° (Regridded from original 0.0833° × 0.0833°)
• Temporal resolution: Bi-monthly (1st–15th and 16th–end of each month)
• Source: https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=2187

Meteorological Data Set (2.Temperature.nc, ... , 6.Cloud_cover.nc)

• Agrometeorological indicators from 1979 to present derived from reanalysis, Copernicus Climate Change Service
• Variable: Normalized Difference Vegetation Index (NDVI)
• Area: Global (60°S ~ 70°N, -180°W ~ 180°E)
• Period: 1982-01-01 ~ 2022-12-31
• Horizontal resolution: 0.25° × 0.25° (Regridded from original 0.1° × 0.1°)
• Temporal resolution: Bi-monthly (1st–15th and 16th–end of each month) 
• The meteorological data were converted from daily values to bi-monthly average values.
• Variables: 2m temperature (K), 2m relative humidity (%), 10m wind speed (m s⁻¹), Precipitation flux (mm day⁻¹), Solar radiation flux (J m⁻² day⁻¹), Cloud cover (dimensionless)
• Source: https://cds.climate.copernicus.eu/datasets/sis-agrometeorological-indicators?tab=overview

Pre-processing code (Set_data_1~3)

• Set_data_1 : Combining raw data for NDVI and checking for missing values in the original data
• Set_data_2 : Combining annual data, calculating semi-monthly averages, and setting the latitude and longitude ranges for meteorological data.
• Set_data_3 : Synchronization of latitude, longitude, and resolution between NDVI and meteorological data.

Analysis code (code1~5)

• code_1 : This script processes climate data for variables by calculating their seasonal anomalies and time-averaged values. It performs the following steps: 
  
  • Monthly Mean Calculation: The script first calculates the monthly mean for each variable over a period of 41 years.
  • Semi-Monthly Mean Calculation: It then computes the semi-monthly mean by combining the monthly mean data.
  • Anomaly Calculation: The script calculates the anomaly by subtracting the semi-monthly mean from the original data.
  • Time Mean Calculation: Finally, the time-mean for the entire time period is calculated for each variable.

• code_2 : This script calculates the linear regression slope, intercept, correlation coefficient (r-value), p-value, and standard error for a given climate variable (in this case, temperature anomaly) over time at each latitude and longitude point. The steps involved are:
  • Load Data: The script loads the input NetCDF file and extracts the time and temperature anomaly (or other climate data) values.
  • Linear Regression: For each spatial point (latitude, longitude), the script performs a linear regression between time and the corresponding climate data to determine the slope, intercept, r-value, p-value, and standard error.
  • Save Results: The regression results are saved into a new NetCDF file with variables for slope, intercept, r-value, p-value, and standard error for each latitude and longitude point.

• code_3 : This script processes NDVI (Normalized Difference Vegetation Index) data by performing the following steps:
  
  • Prepare Heatmap Data: It reshapes the NDVI data into a 4D array of the shape (latitude, longitude, years, 24 months), where each year contains 24 months of data.
  • Compute NDVI Histograms: It computes histograms of the NDVI data for each latitude, longitude, and year, adjusting the NDVI values into 20 bins for analysis.
  • Save Histogram Data: The histogram data is then saved to a .npy file, which stores the data for further analysis.

• code_4 : This script performs k-means clustering on NDVI data, based on histograms of NDVI values:
  1. Load Data: It loads NDVI data and histogram data (NDVI values in bins) from files.
  2. Filter Data: It filters out regions with zero values to focus on areas of interest.
  3. Reshape Data: The data is reshaped into a 2D format to prepare for clustering.
  4. K-Means Clustering: The script applies k-means clustering to the reshaped histogram data.
  5. Mean NDVI Calculation: It calculates the mean NDVI value for each cluster by extracting values from the NDVI data.
  6. Reordering Clusters: The clusters are reordered based on their mean NDVI values.
  7. Save Results: Finally, the script saves the cluster labels and non-zero indices into separate files.

• code_5 : This script processes NDVI (Normalized Difference Vegetation Index) data by clustering and saving the data for each cluster.
  
  • Load Data
    
    • Loads NDVI slope data (slope) from a NetCDF file.
    • Loads precomputed cluster labels (cluster_labels_8.npy) and valid data locations (non_zero_indices_8.npy).
  • Save NDVI Data by Cluster
    
    • Categorizes NDVI data based on clusters.
    • Creates a 2D array for each cluster and assigns NDVI data to the corresponding cluster coordinates.
    • Saves the clustered NDVI data as  .npy files for further analysis.
  • Create Directory and Execute
    
    • Creates the output directory (if it does not exist).
    • Runs the main function to save the clustered NDVI data.

Acknowledgments

This work was also supported by Global - Learning & Academic research institution for Master’s·PhD students, and Postdocs (LAMP) Program of the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (No. RS-2023-00301914).