Landsat-based wheat mapping in the heterogeneous cropping system of Punjab, Pakistan

Wheat is a staple food of Pakistan's population of more than 180 million. The average annual harvest of 24 million tonnes places Pakistan eighth in the world in wheat production. Roughly, 76% of wheat is produced by Punjab province, the breadbasket of Pakistan. The current wheat area and yield reporting system operated by the Punjab Crop Reporting Service (CRS) delivers estimates several months after harvest. The delayed production data cannot contribute to in-season decision support system, such as timely production estimation. However, freely available satellite imagery at medium spatial resolution offers a data source for addressing this limitation. Using Landsat data from the 2013 to 2014 winter wheat growing season and a supervised bagged classification tree approach, we estimated the area of wheat cultivated in Punjab. Validation consisted of a two-stage probability-based cluster field sample. Field data from 110 sample points distributed among twelve 20 km x 20 km blocks were collected. Overall accuracy of the Landsat-based wheat map was 76% with wheat commission error of 38% and wheat omission error of 30%. The Landsat-based map totalled 6.13 Mha of wheat area, and the field-based sample estimate 6.96 +/- 2.15 Mha. Both figures are comparable to the official Punjab CRS figure of 6.77 Mha. The study presents a robust approach for early wheat area estimation providing information relevant to decision support systems concerning food production and trade.