Homogeneity of 20th century European daily temperature and precipitation series

Daily European station series (1901-99) of surface air temperature and precipitation from the European Climate Assessment dataset are statistically tested with respect to homogeneity. A two-step approach is followed. First, four homogeneity tests are applied to evaluate the daily series. The testing variables used are (1) the annual mean of the diurnal temperature range, (2) the annual mean of the absolute day-to-day differences of the diurnal temperature range and (3) the wet day count (threshold 1 mm). Second, the results of the different tests are condensed into three classes: 'useful', 'doubtful' and 'suspect'. A qualitative interpretation of this classification is given, as well as recommendations for the use of these labelled series in trend analysis and variability analysis of weather extremes. In the period 1901-99, 94% of the temperature series and 25% of the precipitation series are labelled 'doubtful' or 'suspect'. In the sub-period 1946-99, 61% of the temperature series and 13% of the precipitation series are assigned to these classes. The seemingly favourable scores for precipitation can be attributed to the high standard deviation of the testing variable, and hence the inherent restricted possibilities for detecting inhomogeneities. About 65% of the statistically detected inhomogeneities in the temperature series labelled 'doubtful' or 'suspect' in the period 1946-99 can be attributed to observational changes that are documented in the metadata. For precipitation this percentage is 90%. Copyright (C) 2003 Royal Meteorological Society.