CropWatch: Global cropping intensity (GCI30, Global - annual – 30 m)

Cropping intensity, defined as the number of cropping cycle(s) per year, is an important indicator to measure arable land use intensity. Tracking the change in cropping intensity can help assess the past development of the food production system and inform future agro-policies. All available images of top-of-atmosphere (TOA) reflectance from Landsat-7 ETM+, Landsat-8 OLI, Sentinel-2 MSI and MODIS during 2016–2018 were used for cropping intensity mapping via the GEE platform. To overcome the multi-sensor mismatch issue, an inter-calibration approach was adopted, which converted Sentinel-2 MSI and Landsat-8 OLI TOA reflectance data to the Landsat-7 ETM+ standard. Then the calibrated images were used to composite the 16-day TOA reflectance time series based on maximum composition method. To ensure data continuity, the MODIS NDVI product was used to fill temporal gaps with the following steps. First, the 250-m MODIS NDVI product was re-sized to 30-m using the bicubic algorithm. Then, the Whittaker algorithm was applied to the gap filled NDVI time series to smooth the NDVI time series. Two phenology metrics were introduced, mid-greenup and mid-greendown, which were derived as the day of year (DOY) at the transition points in the greenup and greendown periods when the smoothed NDVI time series passes 50% of the NDVI amplitude. An interval starting from mid-greenup and ending at mid-greendown is defined as a growing phenophase, and an interval moving from mid-greendown to mid-greenup a non-growing phenophase. Based on this phenophase-based approach, the global cropping intensity at 30m resolution (GCI30) was mapped. The results were validated based on a large number of ground-based samples obtained using GVG (GPS, Video and GIS) smart phone application and other crowd-sourcing dataset. The global cropping intensity dataset at 30m includes two layers. The first layer indicates the average cropping intensity during the three years from 2016 to 2018 with noData value or masked areas assigned to -1. The valid values for the first layer are 1, 2, and 3 representing single cropping, double cropping or triple cropping. The second layer keeps the original total number of crop cycles from 2016 to 2018 with noData value or masked areas assigned to -1. Continuous cropping or number of crop cycles larger than 3 per year are indicated with value of 127. Detailed documentation on the methodology of GCI30 can be found at the following two published papers: https://www.sciencedirect.com/science/article/abs/pii/S0034425720304685 https://essd.copernicus.org/articles/13/4799/2021/