Non-uniform changes in different daily precipitation events in the contiguous United States

This study examines changes in characteristics (amount, frequency, intensity) of daily precipitation in the contiguous United States (CONUS) using high-quality records for a long-term period (1900-2018) and a more recent period (1950-2018) at different temporal (annual and seasonal scales) and different spatial scales (national and sub-regional scales). Results show that the patterns of change during the two periods are very similar. First, on the annual basis, we find an overall increase in the total annual precipitation, frequency of wet days, and intensity of precipitation in both periods in the CONUS, with percentages of stations showing significant increasing trends significantly larger than what can be expected by chance. Second, stations with significant increasing trends are mainly concentrated in eastern CONUS, while stations with decreasing trends are located on the west coast and partial southeast coast. Specifically, the amounts and frequencies of light, moderate, and heavy precipitation mostly have significantly increased at more than 10% of stations. In both periods, there is a non-uniform change for three intensity categories of precipitation, with the frequency and total amount of events with higher intensity showing a larger rate of change, resulting in the smaller contribution of light precipitation to annual total precipitation but larger contribution due to heavy precipitation. Such non-uniform changes can also be observed in most sub-regions and seasons. Moreover, the estimated sensitivities of the amount of light, moderate, heavy precipitation, and heaviest precipitation event to global surface temperature increase for the 1900-2018 period is comparable with that for the 1950-2018 period, indicating that sampling period does not have a substantial effect on the scaling relationship between the amount of different precipitation events and global mean temperature.

Automated summary

This study examines changes in characteristics of daily precipitation in the contiguous United States using high-quality records for a long-term period and a more recent period at different temporal and spatial scales. The results show similar patterns of change during the two periods, with an overall increase in total annual precipitation, frequency of wet days, and intensity of precipitation in the CONUS. Stations with significant increasing trends are mainly concentrated in eastern CONUS, while stations with decreasing trends are located on the west coast and partial southeast coast. The findings also indicate non-uniform changes in different sub-regions and seasons, with heavier precipitation events contributing more to the annual total precipitation.