INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 19: 365–378 (1999) SPATIAL INTERPOLATION OF AIR TEMPERATURE ACCORDING TO ATMOSPHERIC CIRCULATION PATTERNS IN SOUTHEAST FRANCE DOMINIQUE COURAULT a, * and PASCAL MONESTIEZ b a INRA, Unite ´ de Bioclimatologie, Domaine St Paul, Site Agroparc, 84914 A6ignon, Cedex 9, France b INRA, Unite ´ de Biome ´trie, Domaine St Paul, Site Agroparc, 84914 A6ignon, Cedex 9, France Recei6ed 13 January 1998 Re6ised 1 August 1998 Accepted 3 September 1998 ABSTRACT A method is proposed for the interpolation of daily maximum and minimum air temperatures (T x and T n , respectively) at the regional scale, taking into account the atmospheric circulation patterns (CPs). The study region was in southeast France (150 ×250 km 2 ). Daily temperatures measured at 152 meteorological stations were available, and CPs from automatic classification performed every day by Me ´te ´o France from forecast model outputs were used. For the whole of Europe, ten classes centred on France are defined. A geostatistical approach (ordinary kriging) was chosen, because it permits the mapping of the estimation variance for interpolation and consideration of several days at once. Different data processing methods were compared: raw temperatures without correction; temperatures converted to sea level by applying a constant or varying coefficient according to the CP; and sorting days in relation to CP and season. Cross-validation analyses were performed, separating the data set in two independent parts (62 stations for the model calibration and 90 for the validation). These sets of data showed errors from 0.6° to 2°C. An improvement of 0.5°C was observed for the maximum temperature if it was corrected with regard to the elevation and the days sorted according to CP; however, correction of the elevation had a greater effect on improving the results than does CP sorting. The results obtained for the minimum temperatures fluctuate more from day to day. Copyright © 1999 Royal Meteorological Society. KEY WORDS: air temperature; atmospheric circulation patterns; kriging; spatial interpolation; France, southeast; geostatistics 1. INTRODUCTION The air temperature (T air ) measured at 2 m is one of the main input data for many models, such as agrometeorological models for water balance monitoring, crop models for yield prediction, and hydrolog- ical models. This variable plays an important role in the energetic and hydric exchanges at the interfaces between the soil, plants and the atmosphere. Plant growth depends on air temperature, and in crop models, the different phenological stages are determined according to accumulated air temperatures from the sowing date. Temperature thresholds are defined as the temperatures below which there is no development for some crops. In southeast France for example, the threshold for wheat is 0°C, while for maize it is 6°C. When these crop models are applied on a large scale (regional or continental), it is necessary to have sufficiently accurate temperature data. For example, the GOA model (Brisson et al., 1992) used to estimate yield potentials on a European scale for different crops and climates divides the entire territory into 30-km pixels, for which a mean climate is obtained from one to five meteorological stations. Sensitivity studies performed by Ruget et al. (1995) showed that if a systematic error of 91°C/day is made on air temperature during the entire growth cycle of maize, then a yield estimation error of 0.5–1 t/ha will arise, which is significant (Dele ´colle et al., 1995); accurate climatic data are therefore very important. * Correspondence to: INRA, Unite ´ de Bioclimatologie, Domaine St Paul, Site Agroparc, 84914 Avignon, Cedex 9, France. Tel.: +33 4 90316206; fax: +33 4 90899810; e-mail: courault@avignon.inra.fr CCC 0899–8418/99/040365 – 14$17.50 Copyright © 1999 Royal Meteorological Society