Spatial evaluation of crop maps by spatial production allocation model in China

Abstract

Spatial Production Allocation Model (SPAM), developed by International Food Policy Research Institute (IFPRI), is one of broadest spatial models that applied a cross-entropy method to downscale the area and yield for each crop with a resolution of 5 arc minute globally for the year 2000 and 2005.To evaluate the accuracy of three staple crops (rice, wheat and maize) in China allocated by SPAM, we compared these crop maps with remote sensed cropland derived from national land cover datasets. This is done through a comparison scheme that accounts for spatial difference at the pixel level. Four types (no-existing, mis-allocated, over-estimated and reasonable) were formulated in this scheme that was used to evaluate the per-pixel area accuracy of each of the three crops on national and provincial scales. Overall, the map of maize has the highest area accuracy with a 64% percentage of reasonable pixels that covers 96% of the total maize area, in contrast, 57% (90%) and 44% (81%) for the wheat and rice map respectively. Further, crop area consistency in rain-fed cropland is better than that in irrigated cropland. Through the evaluations, we can provide decision makers with information on the SPAM products exist as well as the strengths and weaknesses. Meanwhile, some recommendations can be concluded on priorities for further work on the improvement of the reliability, utility and periodic repeatability of crop distribution products.

Assessing the Response of Satellite Solar-Induced Chlorophyll Fluorescence and NDVI to Impacts of Heat Waves on Winter Wheat in the North China Plain

“…Using a classic cross-entropy approach, the SPAM makes plausible allocations of crop production in geopolitical units (country or state) into individual pixels through judicious interpretation of all accessible evidence such as production statistics, farming systems, satellite images, crop biophysical suitability, crop prices, local market access, and prior knowledge. e 5-by-5-minute resolution maps obtained with the SPAM for major crops agreed well with validated groundbased results [44][45][46]. e MODIS land cover data includes 17 land cover types: 11 natural vegetation classes, 3 developed and mosaicked land types, and 3 nonvegetated land types [47].…”

Mapping Export-Oriented Crop Production

“…MapSPAM data is extensively evaluated by several institutions for plausibility (see You et al 2014b), yet these evaluations were mainly qualitative or semi-quantitative in nature. We are only aware of one independent and quantitative assessment of the MapSPAM data by Tan et al (2014), who compared the accuracy of the crop maps with empirical case study results for China and found a satisfactory agreement. Regarding the FAO trade data, we rely on the data from Kastner et al (2014) that circumvents the common problem of bilateral trade data by tracing the primary origin of imported agricultural produce, linking crops to their actual places of consumption.…”