Satellite analysis of France's 2003 Heatwave


Ben ZaitchikAlison MacaladyLarry BonneauRon Smith


In this project CEO researchers used MODIS and ASTER imagery, in combination with basic meteorological data, to map surface impacts and land-atmosphere feedbacks associated with the severe French heatwave of 2003. Analysis of MODIS-derived vegetation index and surface temperature indicated that the impacts of the summertime heatwave were greatest in central France, in a region that is transitional between the Mediterranean climate zone in the south of the country and the Atlantic-influenced climate zone in the north (Figures 1&2).

These data were combined with NCEP/NCAR Reanalysis records of air temperature and wind speed to estimate the 2003 anomalies in surface sensible and radiative heat flux. Both of these fluxes were significantly enhanced during the heatwave, indicating a local positive feedback on air temperature that was greatest in the transitional climate zone. Hypotheses regarding soil-moisture precipitation feedbacks during extreme drought were also examined, and results are reported in an upcoming paper. ASTER imagery was used to zoom in on land use patterns in the affected area (Figure 3). It was found that both impacts and land-atmosphere feedbacks were more severe in agricultural areas than in forest patches, suggesting that land management played an important role in the development of the heatwave.

Figure 1

Spatial distribution of the 2003 anomaly in normalized difference vegetation index (NDVI; unitless) calculated from MODIS 16-day composites for:
   (A) April 23 - May 8, (B) June 10 - 25, (C) July 12 - 27 and (D) August 13 - 28.

Ecological zones are outlined in gray, with the Atlantic-influenced zone in the north (ATL), Mediterranean zone in the south (MED) and transitional zone in the center of France (TRN). The footprint of ASTER images used in the study is indicated by the black box.

Figure 2

As in Figure 1, but for the spatial evolution of the 2003 radiometric temperature anomaly based on 8-day MODIS composites for:
   (A) April 15 - 22, (B) June 10 - 17, (C) July 12 - 19 and (D) August 5 - 12.

Figure 3

Level 2 ASTER products for a subset of the image footprint.
(A,B) Atmospherically corrected surface reflectances displayed as 321-RGB false color composites for the (A) August 1, 2000 and (B) August 10, 2003 images. Vegetation appears red due to high reflectance in the near-IR (ASTER band 3).
(C,D) ASTER-derived kinematic surface temperature for the same (C) 2000 and (D) 2003 scenes.

Note the large contrast between agricultural lands and forest patches in the 2003 image. Scale bar (in D) indicates 500 m and applies to all four images.

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19 July 2005