The impact of the heat wave of summer 2003 in SW Europe as observed from satellite imagery

The extraordinary meteorological conditions of summer 2003 provide a singular case of study of the response of vegetation to drought under conditions that are similar to what is expected by some scenarios to be a normal summer by the latter decades of the 21st century. After collecting climatic and meteorological information to produce monthly fields of mean temperature, precipitation and precipitation deficit (as the difference between precipitation and potential evapo-transpiration), we have analyzed a monthly series of fields of normalized difference vegetation index (NDVI). Our results indicate strongly negative anomalies of satellite NDVI: a 25% of the area covered by herbaceous vegetation had a relative anomaly of NDVI in August lower than −17%, while the equivalent value for deciduous forests was −11%. Geographically, the most affected area was located to the SE of a diagonal line crossing France from SW to NE. As low values of NDVI in August indicate early leaf withering, some deciduous forests experienced a serious reduction of the number of valid days for photosynthesis.