Monitoring of the 2003 summer drought in Belgium with the NDWI applied on spot-vegetation data.

The summer 2003 was abnormally hot, sunny and dry. The average temperatures from June to August were the highest ever recorded in the Belgian reference meteorological station of Uccle, but also in other countries of western and central Europe such as Portugal, Germany, Switzerland and the United Kingdom. Many human activities were affected by these particular climatic conditions, among which agriculture.The Normalized Difference Water Index (NDWI) applied on ten-daily SPOT- VEGETATION imagery is one of the drought indicators which
could serve for the localisation of drought affected areas in Belgium. In this paper preliminary results show that detection of dry events is possible using historical averages of NDWI. Relative NDWI images can be used to monitor the development of the summer drought.These images are computed by the weighted difference between the NDWI values during this summer and its value at the same period in a reference year, which corresponds to a normal year in terms of rainfall availability. Analysis of the relation between NDWI and NDVI behaviours show that the green biomass influences the NDWI value especially during the growing season. More accurate
study has to be done to individualize the specific NDWI behaviour during dry events. In perspectives, index validation with meteorological parameters and with the Relative Soil Moisture Index, which is an output of the Belgian Crop Growth Monitoring System, will improve this study.