Résumé - La chaleur et la sécheresse 2003 : une synthèse climatique. Températures et sécheresse ont été extrêmes en Europe durant l'été 2003. Les valeurs les plus anormales ont été atteintes par les températures maximales en juin et en août. La répartition spatiale des anomalies de température montre des similarités frappantes entre ces deux mois dans les zones les plus concernées. Des températures généralement supérieures à la normale ont régné sur une grande partie de l'Europe centrale et occidentale de mai à septembre 2003. Le déficit des précipitations a été particulièrement prononcé durant l'été 2003, mais a duré de février 2003 à juin 2004. L'insolation a été supérieure à la normale, non seulement durant l'été mais durant toute l'année 2003. La sécheresse qui a touché la végétation durant l'été 2003 a été renforcée par la durée prolongée du déficit de précipitations et d'humidité, par les températures extrêmement élevées durant l'été ainsi que des valeurs élevées d'insolation.International audienceHeat and drought were extreme in summer 2003 in Europe. Climatic data show that most extreme were maximum air temperatures in June and August; maps of these two months show a striking similarity in geographical range. Over wide regions, monthly mean temperatures were more than 4 ◦C above the long term mean values. The heat lasted from May to September in large parts of western and central Europe. The lack of precipitation was most severe in summer 2003 but precipitation was generally below normal from February 2003 until June 2004 (with the exception of two months). Sunshine duration was above normal, particularly in regions which usually have rainy and cloudy episodes in summer, and relative air humidity was below normal during the whole year of 2003. The drought experienced by the vegetation in summer 2003 was exacerbated by the length of the period with scarce precipitation and humidity, by the heat during the summer and by long sunshine duration

The power law is most often applied to extrapolate the near‐surface wind speed to the wind turbine hub height. Due to variations of the meteorological conditions, the power law exponent varies over time. Usually, no long‐term wind speed measurements from multiple heights are available which would allow time‐dependent and spatially explicit power law exponent estimations. Instead, often the mean of the power law exponent or a constant value of 0.14 is assumed. The goal of this study was to quantify the error in wind potential assessments resulting from applying the mean of the power law exponent or a value of 0.14. The data base for this study are the hourly wind speed time series at 10 and 100 m above ground available for the period 2007 to 2018 from the ERA5 reanalysis project at a global 0.25° × 0.25° grid. The errors in the estimation of the wind power density and the capacity factor were calculated. It was found that, onshore, the global median of the absolute percentage error related to the wind power density using the mean of the power law exponent is 7.5%. Assuming a constant value of 0.14, the power law is less accurate (absolute percentage error: 37.1%). For the estimation of the capacity factor the absolute percentage errors are 5.5% and 36.9%. Based on the results of this study, the use of time‐dependent and spatially explicit power law exponents is suggested. In the absence of long‐term wind speed measurements from multiple heights, the results provide a comprehensive global overview of the errors to be expected from using the mean of the power law exponent or assuming a value of 0.14. In many regions where the wind resource is abundant, using the mean of the power law exponent only leads to minor errors in capacity factor estimation. There, the assessment of wind resources with small errors is possible, even in the absence of long‐term wind speed measurements at different heights.