Evaluating salinity damage to crops through satellite data analysis: application to typhoon affected areas of southern Japan

In recent times, tsunamis and typhoons have threatened Japan's coastal lands with increased flooding and salinity. Using satellite data, we monitored the effect of increased salinity on vegetation health in the coastal area of southern Japan, which was affected by flooding following Typhoon 9918 in 1999. An index of plant activity called the Normalized Difference Vegetation Index (NDVI) was evaluated before and after the typhoon, and the change in NDVI was computed as a comparison measure. The results were then correlated with electric conductivity, which is a measure of soil salinity. A strong negative correlation was found between NDVI ratio and salt concentration (r = - 0.7731, n = 50, p < 0.0001), indicating that the reduced NDVI values were attributable to increased salinity from the flooding. These results not only provide useful insight into a rapid method of assessing large-scale flood impacts using satellite data, but also validate the monitoring of NDVI as an indicator of salinity damage to vegetation. To summarise, by understanding the changes in vegetation health following natural disasters such as flooding (as revealed by NDVI), we can potentially develop improved management strategies.