PHILIPPINES: Super Typhoon Haiyan Causes Marginal Food Crop Losses

The USDA has been conducting an ongoing assessment of damages in the central Philippines owing to super-typhoon Haiyan, and as a result it reduced its estimate of total 2013/14 milled rice production in December to 11.64 million tons - down 60,000 tons or 0.5 percent. Corn production in 2013/14 was also reduced to 7.32 million tons, down 35,000 tons or 0.5 percent owing to typhoon damage. The current national rice and corn area estimates are 4.67 and 2.57 million hectares respectively, down 80,000 and 30,000 hectares compared to last month. These extremely marginal reductions are largely in line with recent reports produced by the Philippine Department of Agriculture, which indicate approximately 80,000 hectares of immature rice and 22,000 hectares of corn were lost in the Visayas region in the aftermath of the storm. Typically during the October-December 4th quarter growing period, the Visayas region harvests approximately 327,000 hectares of rice and 90,000 hectares of corn. Based on this data, typhoon Haiyan destroyed roughly 24 percent of quarterly rice and corn area in the region. On a national basis, however, these losses represent only 2 percent of total Philippine rice area and less than 1 percent of corn area. Despite the devastating humanitarian and infrastructural impact Haiyan had throughout the Visayas, it proved less consequential to the nation’s agricultural sector and does not pose any threat to the current food security picture. As reported earlier, this record-setting category 5 super-storm churned through one of the least intensively cultivated areas in the Philippines, sparing major agricultural growing regions both north (Luzon) and south (Mindanao). This report provides some of the geospatial end-products produced by the USDA analysis.

NASA’s MODIS satellite (above) provided one of the best regional overviews of the after-effects of typhoon Haiyan on the natural landscape. This composite image clearly delineates areas which sustained severe loss of vegetative landcover from gale-force winds and coastal storm surge. The islands are largely forested, with considerable land areas in Samar, Leyte, Cebu, and Payan being heavily damaged. Even at the relatively coarse 500-meter resolution in this MODIS imagery, this storms destructive power is visible from space.

The MODIS imagery was also invaluable in illustrating the variation in damage to vegetation throughout the region, enabling analysts to identify and roughly delineate areas sustaining the worst affects. The satellite-derived vegetation index uses the normalized difference vegetation index (NDVI) from NASA's MODIS Terra satellite. It is obvious from the change-detection analysis of satellite images from before and after typhoon Haiyan that sizable areas on the islands of Samar, Leyte, and Payan experienced extremely negative changes to the overall landscape, which are indicative of severe damage to or loss of vegetative cover.

USDA analysts further refined the NDVI change-detection analysis by filtering it with known agricultural growing areas, and thus isolating the NDVI data to farmlands. These agricultural zones were extracted from detailed geospatial landcover datasets produced by the University of Maryland in 2012 and by MDA Federal, Inc in 2000 (Geocover LC). The map above illustrates the changes occurring on farmlands in the Visayas from mid-October to mid-November. This data helped USDA determine the location of potential crop losses and obtain a perspective on the spatial extent or scope of total areas affected. One caveat to keep in mind, however, is that the NDVI data used in this analysis covered a period of approximately 4 weeks. Any natural change occurring during that period involving the maturation (senescence) of crops or alteration of the landscape to prepare for planting (cultivation) would also cause a decline in NDVI. Therefore, it cannot be categorically stated that all negative change illustrated in the above map was a direct result of super-typhoon Haiyan. However it is logical to assume that a great deal of it is associated with the storm given the areas showing the greatest change are directly in the path of the storm, while nearby agricultural areas do not show the same negative pattern.

The NDVI change-detection analysis was further refined in a few areas where relatively cloud-free higher resolution satellite imagery was available. In this case USDA made use of 30 meter data from the Landsat-8 satellite to evaluate the change in vegetation over agricultural areas in eastern Panay island. This area produces a variety of field crops, including both rice and corn. As can be seen from the resulting map above, both positive and negative changes occurred on these farmlands near the city of Iloilo during the analysis period (Oct. 20 – Nov. 21, 2013). The negative areas may indicate crop damage or harvest/cultivation activity, while positive change would indicate strong recent crop growth. The bulk of the negative areas appear to fall within the rice growing areas defined by the landcover datasets.

One of the independent post-disaster data sources which became available to the USDA following typhoon Haiyan was a flood analysis from the Copernicus Sentinel system, a constellation of satellites from the European Commission's Earth Observation Program. This flood analysis was performed immediately following typhoon Haiyan utilizing 20 meter resolution satellite imagery. USDA cross-referenced the digital Copernicus flood-extent data with the agricultural landcover data mentioned earlier to determine how much farmland had been inundated on the islands of Panay and Negros. As can be seen from the map above, a little over 9,000 hectares of crop land is estimated to have experienced some degree of flooding.

An additional data source which provided valuable insight of field crop conditions immediately following typhoon Haiyan was the very-high resolution satellite imagery provided by DigitalGlobe. USDA acquired a number of 2-meter resolution images from DigitalGlobe’s WorldView 2 satellite over key agricultural cropping areas on Leyte, Negros, Payan, and Bantayan islands. These images allowed USDA analysts to evaluate the growth stage and condition of field crops, as well as the prevalence of crop damage associated with the storm. The average size of a typical rice farm in this region is somewhere between 0.5-1.5 hectares, with individual crop fields being significantly smaller. The 2-meter resolution WorldView 2 imagery allowed USDA not only to visualize field boundaries on some of the smallest agricultural fields in the world, but evaluate vegetative crop conditions within these tiny areas as well. The satellite images have been displayed in a manner (falsecolor infrared) which portrays vegetation as a range of red colors. Humans can distinguish more variations of the color red than any other, and thus falsecolor infrared imagery is especially useful to agricultural analysts by highlighting subtle differences in crop conditions. The sample images provided here (above and below) were annotated to show examples a few of the discernable characteristics which are widely evident in various areas throughout the images (H=harvested; E=emerging; M=maturing; C=cultivated; D=damaged; N=non-crop vegetation).

Authorities from the Philippine Department of Agriculture and the International Rice Research Institute (IRRI) reported that much of the rice crop grown in the Visayas region had been harvested prior to typhoon Haiyan’s arrival on November 8th. It is also assumed that the majority of the corn crop was also harvested by the end of October. What became clear after evaluating the sample of high-resolution WorldView 2 imagery USDA has access to was that a large proportion of the crop land in the region did appear to have been harvested or idle immediately following the storm. And in most areas that had actively growing crops, there was visible evidence of both crop damage and crops which escaped virtually unscathed.

Additional information:

http://www.pecad.fas.usda.gov/highlights/2013/11/Philippines/
http://gain.fas.usda.gov/Recent%20GAIN%20Publications/Typhoon%20Haiyan%20Damage%20Summary_Manila_Philippines_12-4-2013.pdf

Current USDA area and production estimates for grains and other agricultural commodities are available on IPAD's Agricultural Production page or at PSD Online.