Diurnal and seasonal patterns of global urban dry islands

Abstract Urban heat islands (UHIs) are a widely studied phenomenon, while research on urban-rural differences in humidity, the so called urban dry or moisture (UDIs, UMIs), is less common and large-scale quantification of seasonal diurnal patterns UDI still lacking. However, UDI/UMI effect essential to understand impacts humidity outdoor thermal comfort, building energy consumption, ecology cities worldwide. Here, we use set globally distributed air temperature measurements (1089 stations) quantify UHI resulting from rapid urbanization over many regions world. The terms ‘absolute UDI’ ‘relative defined, which urban–rural actual relative metrics, respectively. Results show that absolute largest during daytime with peak decrease areas occurring late afternoon hours. In contrast, night (RH) vapor pressure deficit (VPD) increase occurs evening hours values around ?10% ?11% for RH 2.9–3.6 hPa VPD between 20–00 local time summer. Relative UDIs warm season, except UDI, does not any pattern. agreement literature, canopy shown be nighttime larger summer than winter. predominantly caused by changes day nighttime.