Satellite Technology for Vegetation Drought Monitoring in Taiwan

Abstract

This study collected the climate data recorded by 355 precipitation stations all over the island of Taiwan from January of 1991 to October of 2002 and 54 satellite images of NOAA taken in the period of 1995-2001. The normalized difference vegetation index (NDVI), vegetation condition index (VCI), temperature condition index (TCI), and drought index (DI) were calculated from satellite data. The correlation between precipitation and DI was analyzed. Based on forest type, Taiwan may be divided into 4 regions, i.e., north, center, south, and east. The forest vegetations were recognized as hardwood forest, softwood forest, artificial softwood forest, grass, and mixed forest. The calculated value of NDVI in winter (November-January) was the minimum, whereas that in summer (May-July) was the maximum. Therefore, changes of NDVI may reflect the conditions of drought. There is no difference in DIs among various regions in all seasons, but the northern area showed a slightly higher DI in summer. DIs of central and eastern regions were higher than those of northern and southern regions in autumn. The values of DI calculated from eastern region showed the highest discrepancy between autumn and winter. Results suggest that satellite images of forest vegetation provide information about drought progression status and may be used to establish an early drought forecasting system.