A global map of rainfed cropland areas (GMRCA) at the end of last millennium using remote sensing |
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| Authors: | Chandrashekhar M Biradar Prasad S Thenkabail Praveen Noojipady Yuanjie Li Venkateswarlu Dheeravath Hugh Turral Manohar Velpuri Murali K Gumma Obi Reddy P Gangalakunta Xueliang L Cai Xiangming Xiao Mitchell A Schull Ranjith D Alankara Sarath Gunasinghe Sadir Mohideen |
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| Institution: | 1. Center for Spatial Analysis, University of Oklahoma, Norman, OK, USA;2. U.S. Geological Survey (USGS), Flagstaff, Arizona, USA. Formerly, IWMI, Colombo, Sri Lanka;3. Department of Geography, University of Maryland, College Park, MD, USA;4. International Water Management Institute, Colombo, Sri Lanka;5. On the Street Productions, North Carlton, Melbourne 3054, Australia;6. GIS Center of Excellence, South Dakota State University, Brookings, SD, USA;g National Bureau of Soil Survey and Land Use Planning, Indian Council for Agricultural Research, India;h College of Water Resources and Hydropower, Wuhan University, Wuhan, China;i Department of Geography and Environment, Boston University, Boston, MA, USA |
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| Abstract: | The overarching goal of this study was to produce a global map of rainfed cropland areas (GMRCA) and calculate country-by-country rainfed area statistics using remote sensing data. A suite of spatial datasets, methods and protocols for mapping GMRCA were described. These consist of: (a) data fusion and composition of multi-resolution time-series mega-file data-cube (MFDC), (b) image segmentation based on precipitation, temperature, and elevation zones, (c) spectral correlation similarity (SCS), (d) protocols for class identification and labeling through uses of SCS R2-values, bi-spectral plots, space-time spiral curves (ST-SCs), rich source of field-plot data, and zoom-in-views of Google Earth (GE), and (e) techniques for resolving mixed classes by decision tree algorithms, and spatial modeling. The outcome was a 9-class GMRCA from which country-by-country rainfed area statistics were computed for the end of the last millennium. The global rainfed cropland area estimate from the GMRCA 9-class map was 1.13 billion hectares (Bha). The total global cropland areas (rainfed plus irrigated) was 1.53 Bha which was close to national statistics compiled by FAOSTAT (1.51 Bha). The accuracies and errors of GMRCA were assessed using field-plot and Google Earth data points. The accuracy varied between 92 and 98% with kappa value of about 0.76, errors of omission of 2–8%, and the errors of commission of 19–36%. |
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| Keywords: | Global mapping GMRCA Rainfed and irrigated croplands Remote sensing Sub-pixel areas |
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