Quantifying the urbanization induced temperature effect of weather station De Bilt (Netherlands) between 1900-2000

Many cities around the world have spatially expanded during the 20th century. Consequently, some weather stations are currently located closer to cities than before. Since most cities ex-perience urban heat island effects, it has been hypothesized that those weather stations show a positively biased temperature trend due to urbanization. In this study, we estimate this effect for WMO station De Bilt, using the mesoscale model WRF. This station has been selected because it has a long and accurate historical record and is located close to the city Utrecht, which sub-stantially expanded in the 20th century. The temperature rise due to urbanization is determined by conducting model simulations for the land use situations for both the year 1900 and 2000. This is repeated for four different epi-sodes lasting a week, each representing a typical large-scale flow regime. By using frequency distributions of the Grosswetterlagen, an average temperature rise is estimated. The results indicate that the urbanization during the 20th century has resulted in a temperature rise of 0.32±0.06 K. This rise is much higher than estimated by comparing observed tempera-ture records close to De Bilt, which suggested only 0.11K ± 0.06 K. The modeling study also re-veals a larger temperature rise in the winter, due to the contribution of anthropogenic heat.