Modelling the influence of urbanization in the 20th century on the temperature record of weather station De Bilt (Netherlands)

Many cities around the world have spatially expanded during the 20th century, and therefore some weather stations have become located closer to cities than before. Due to the urban heat island effect (UHI), those weather stations may show a positive bias in the 2 meter tem-perature record. In this study we estimate the urbanization induced impact on temperature record of WMO station De Bilt (The Netherlands). This station has a long historical record, but the nearby city Utrecht and accompanying suburbs substantially extended in the 20th century. Particularly, Utrecht expanded spatially about a factor 4. The temperature rise due to urbanization is estimated by conducting WRF model simulations for the land use situation for both 1900 and 2000. This is repeated for seven different episodes of a week, each representing a typical large-scale flow regime, and subdivided per season. By using frequency distributions of the Grosswettertypen an average temperature rise is estimated. The model results with the best performing atmospheric boundary-layer scheme (MRF), indicates that the urbanization during the 20th century has resulted in a temperature rise of 0.22±0.06 K. This result is much higher than the estimated trend by comparison of observed temperature records nearby De Bilt, which suggested 0.10±0.06 K. The study also reveals that a strong urbanization effect from Utrecht occurs in winter, due to the contribution of anthropogenic heat.