Quantifying and adjusting the impact of urbanization on the observed surface wind speed over China from 1985 to 2017

Abstract

The observed surface wind speed (SWS) has declined across China over the last four decades, but the mechanisms responsible for this decline have been explored without reaching a consensus. In this study, we develop a physical method to quantify and adjust for the impact of urbanization around weather stations on the observed SWS over China from 1985 to 2017. The urbanization impact factor on the SWS is calculated based on Monin–Obukhov similarity theory, and the aerodynamic roughness length and zero-plane displacement height at each weather station are calculated yearly based on a 30-meter resolution satellite land cover product. The results show that urbanization around weather stations reduces the observed SWS by 11% on average over China. The urbanization impact on the observed SWS is the highest in southeastern China at 19% and the lowest over the Tibetan Plateau at 4%. Urbanization decreases the observed SWS by 9% over northwestern China and by 12% over northeastern China, northern China and southern China. More importantly, the proposed method can easily adjust for the urbanization impact on the observed SWS. After adjustment, the SWS appears to have started recovering during the 1990s, and the decreasing trend of SWS during the study period is nearly zero. The results shown here indicate that the observed decreasing trend of SWS from 1985 to 2017 over China is an observational local bias and does not reflect large-scale climatic variation. This inference is also consistent with geostrophic wind theory predictions; i.e., SWS exhibits strong decadal variability, but its long-term trend is negligible.