Assessment of paddy fields' damage caused by Cyclone Nargis using MODIS time-series images (2004-2013)

The Ayeyarwady Delta in the Bay of Bengal, the rice bowl of Myanmar, depends on natural conditions, especially rainfall. During the dry season, the delta's coastal zone experiences saline water intrusion due to its low-lying topography. On May 2, 2008, Cyclone Nargis made landfall and crossed Ayeyarwady Region and Yangon City, affecting more than 50 townships and causing massive destruction of personal property and natural ecosystems. There is no doubt that Nargis caused an unprecedented large-scale disaster, but there is no objective method to quantify crop yield and salinity damage in the delta post-Nargis. The purpose of this study, therefore, is to clarify the changes in vegetation in paddy fields in the Ayeyarwady Delta using Moderate Resolution Imaging Spectroradiometer data pre- and post-Nargis and determine whether this method can be applied to measure crop and salinity damage. The study used daily composite data at a 250-m resolution (MOD09GQ, collection 6) from 2004 to 2013 and calculated NDVI and salinity indices smoothed by locally weighted regression (Lowess). Based on the results of our studies, NDVI peak value in 2008 was lower by 19% compared to 2007 data, and that the NDVI peak values declined for three straight years since May 2008 when Nargis struck. However, salinity damage evaluation pre- and post-Nargis (using the salinity index equation) showed that soil electrical conductivity did not tend to move up in the post-Nargis dry season (2009), indicating that the decrease in NDVI values was not due to salinity damage.