Reassessing Hourly Precipitation-Temperature Scaling: The Diurnal Cycle in a Warming China

Hourly extreme precipitation is expected to intensify with global warming following Clausius-Clapeyron (CC) relationship. In this research, we utilized hourly precipitation and dew point temperature (DPT) data from over two thousand in-situ gauge observations spanning 1950–2018, as well as ERA5 and MERRA2 datasets, during the warm season across mainland China. Our observations clarify the spatial distribution and trend of hourly extreme precipitation in China mainland, derive the precipitation-temperature scaling relationship, and, for the first time, explore the diurnal cycle of scaling from observations, which has received limited attention in previous studies. Hourly extreme precipitation increases more significantly than at daily time scale, enhancing the probability and risk of short-term extreme precipitation events.

 For hourly precipitation-temperature scaling relationship, 88.7% of stations exhibit super-CC scaling with notable regional differences. Extreme precipitation intensity increases monotonically with DPT and no ‘hook’ structure is observed in the regional scaling curve. However, ERA5 and MERRA2 predominantly show stations with sub-CC scaling, and exhibited a ‘hook’ structure at DPT about 22℃ in regional scaling curve, suggests that reanalysis datasets underestimate changes in hourly extreme precipitation in response to DPT. Noticeably, The scaling shows a pronounced diurnal cycle and exceed all-hours scaling, indicating that the mix of precipitation from different hours ultimately affects overall scaling results. Over a 39-year period, changes in extreme precipitation intensity were closely aligned with DPT throughout the diurnal cycle in inland regions. These result provides valuable insight into the shift of extreme precipitation to morning/night in some regions under climate change.