Both meteorological methods and remote sensing methods contain some deficiencies in monitoring agricultural
drought. To improve the accuracy of the agricultural drought monitoring, the comprehensive monitoring model
was established based on the relationship between the standardization vegetation, supply water index (VSWIs),
the comprehensive precipitation index (CPI) and the synchronous soil moisture data measured in the study area.
The VSWIs was effective in monitoring drought at high density vegetation areas and the CPI was suitable to the
tropical area. The root mean square error (RMSE) and the relative root mean square error (RMSEr) of the
model were 4.65% and 19.28% respectively. The model was then used to evaluate the change of the agricultural
drought in Hainan Island from October 2004 to January 2005. The results indicated that the drought in the
study area had significant spatial and temporal differences. The droughts in the west and the north were more
serious than those in the east and the south of the island respectively, and the drought in the plain was more
serious than that in the mountain area. Temporally the drought intensified from early October 2004. Until late
January 2005, the drought was still very serious. The drought approached its peak in early December 2004. The
heavy drought area of paddy fields, dry land and other woodland accounted for about 59%, 61% and 20%
respectively. Crop growth was constrained obviously by this drought. Compared with last year, the cumulative
value of normalized difference vegetation index (NDVI) was reduced by 6.34%, and yield of the natural rubber
was reduced about 1.16×104t from October to December in 2004.