CALCULATING REGIONAL CLIMATIC TIME-SERIES FOR TEMPERATURE AND PRECIPITATION - METHODS AND ILLUSTRATIONS

Various methods for combining station temperature and precipitation ti me series into regional series are examined. Interpolation of the stat ion series on to regular grid-boxes of some kind reduces the effects o f both spatial and temporal changes in station coverage. Regional time series are best produced by using anomaly or standardized anomaly val ues rather than the raw values. For temperature, and for spatially coh erent regions in terms of precipitation variance, the exact method doe s not seriously affect the resulting time series, provided anomalies a re used, although the magnitudes of trends may differ. For regions wit h large spatial variations in precipitation variance, the additional s tep of standardizing the anomaly values is recommended. Both anomaly a nd standardized anomaly series can be easily transformed back to the o riginal units, although the exact method for doing so can alter the re sulting time series in non-trivial ways.