Hourly extreme precipitation changes under the influences of regional and urbanization effects in Beijing

Short duration extreme precipitation has devastating impacts on city area. Local urbanization effects, superimposed upon regional climate change, complicate examination of long-term changes in short duration precipitation extremes in urban areas. Based on high-quality rain gauge observations of summer time hourly precipitation in Beijing Region over 1977-2013, this study reveals that despite the general drying tendency for North China, the urban area of Beijing has experienced more hourly precipitation extremes (HPE) than the suburban area since 2004, coinciding with the surge in the growth of urban built-up areas. These hourly urban precipitation extremes are increasingly inclined to occurring during night-time, especially during 1800 LST to 0200 LST (UCT+8). On the one hand, the amplified urban heat inland effect, which was more significant at night-time, seems to have facilitated formation of more intense small scale thermal-low and resultant ascending branch; on the other hand, it has favoured to establishing unstable stratification in the lower level. This possible mechanism explains the preference of HPE in urban areas during night-time and climate change diversity under the influence of megacity superposition.