Positive Correlation Between Wet-Day Frequency and Intensity Linked to Universal Precipitation Drivers

Understanding precipitation is essential for quantifying weather and climate-related risks. Changes in precipitation climatology are typically based on independent analysis of precipitation frequency and intensity. Here we show that where it rains more often, it also rains harder. When grouping global precipitation reanalysis data and observations from the past 40 years into regions of similar wet-day frequency, regardless of geographical separation, there is a strong correlation with wet-day intensity distributions. These wet-day-frequency regions are also more physically coherent than regions based on geographical location. We find the coherent relationship between wet-day frequency and intensity distributions is partially explained by wet-day-frequency regions having similar vertical velocity and convective available potential energy distributions, once polar regions are excluded. These represent dynamic and thermodynamic processes that indicate how conducive wet-day-frequency regions are to large-scale and convective precipitation. This suggests that the main drivers of precipitation are universal. We also show that extreme-precipitation metrics are dependent on wet-day frequency within our framework. Our results imply that wet-day frequency could be used to derive estimates of extreme-precipitation climate indices and corresponding uncertainties, these uncertainties being related to local processes.