RT Journal Article T1 Quality control and homogeneity of precipitation data in the southwest of Europe A1 González Rouco, Jesús Fidel A1 Jiménez, J. L. A1 Quesada, Vicente A1 Valero Rodríguez, Francisco AB A quality control process involving outliers processing, homogenization, and interpolation has been applied to 95 monthly precipitation series in the Iberian Peninsula, southern France, and northern Africa during the period 1899- 1989. A detailed description of the procedure results is provided and the impact of adjustments on trend estimation is discussed. Outliers have been censored by trimming extreme values. Homogeneity adjustments have been developed by applying the Standard Normal Homogeneity Test in combination with an objective methodology to select reference series. The spatial distribution of outliers indicates that they are due to climate variability rather than measurement errors. After carrying out the homogeneity procedure, 40% of the series were found to be homogeneous, 49.5% became homogeneous after one adjustment, and 9.5% after two adjustments. About 30% of the inhomogeneities could be traced to information in the scarce history files. It is shown that these data present severe homogeneity problems and that applying outliers and homogeneity adjustments greatly changes the patterns of trends for this area. PB American Meteorological Society SN 0894-8755 YR 2001 FD 2001 LK https://hdl.handle.net/20.500.14352/59911 UL https://hdl.handle.net/20.500.14352/59911 LA eng NO © 2001 American Meteorological Society. This work was supported by Project Number CLI97-0558, Comunidad de Madrid, and Fundación Ramón Areces. The authors also thank P. Brandt, P. Cuesta, M. Widmann, and E. Zorita for their comments on the original version of the manuscript. We thank also F. Zwiers and the two anonymous reviewers for their valuable comments and suggestions. NO Comunidad de Madrid NO Fundación Ramón Areces DS Docta Complutense RD 8 abr 2025