A synthesis of hourly and daily precipitation extremes in different climatic regions

Climatological features of observed annual maximum hourly precipitation have not been documented systematically compared to those on daily timescales due to observational limitations. Drawing from a quality-controlled database of hourly records sampling different climatic regions including the United States, Australia, the British Isles, Japan, India and peninsular Malaysia over the 1950-2016 period, we examined climatological features of annual maximum precipitation (AMP) across timescales ranging from 1-hr (AMP(1-)(hr)) to 24-hr (AMP(24-)(hr)). Our analysis reveals strong relations between the magnitude of AMP and the climatological average annual precipitation (AAP), with geographic variations in the magnitude of AMP(24-)(hr) across topographic gradients not evident in AMP(1-)(hr). Most AMP(1-)(hr) are found to be embedded within short-duration storms (>70% of AMP(1-)(hr) are embedded within 1-5 h storms), especially in regions with low AAP and in the tropical zone. Likewise, most AMP(24-)(hr) are found to be the accumulation of a very limited number of wet hours in the 24-h period (>80% of AMP(24-)(hr) are due to storms lasting <15 h) across many parts of the sampled regions, highlighting the added-value of hourly data in estimating the actual precipitation intensities. The seasonal distribution of AMP may change across different timescales at a specific location, reflecting the prevalence of different seasonal triggering mechanisms. We also find that most AMP(1-)(hr) occur preferentially in late afternoon to late evening, slightly later than the usual mid-to-late afternoon peak in the mean precipitation intensity. Finally, analysis of atmospheric instability, realized through the convection available potential energy (CAPE), reveals that CAPE is higher before AMP(1-)(hr) with respect to AMP(24-)(hr), although the response of precipitation intensity seems to saturate at higher CAPE levels, a feature evident both in the tropical and extratmpical zones. This study provides insights on climatological features of hourly precipitation extremes and how they contrast with the daily extremes examined in most studies.