Trends in extreme rainfall over the past 55 years suggest springtime sub hourly rainfall extremes have intensified in Mahantango Creek, Pennsylvania

Authors: Buda, Anthony; Millar, David; Kennedy, Casey; Welsh, Molly; Wiegman, Adrian

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2024
Publication Date: 11/13/2024
Citation: Buda, A.R., Millar, D.J., Kennedy, C.D., Welsh, M.K., Wiegman, A.R. 2024. Trends in extreme rainfall over the past 55 years suggest springtime sub hourly rainfall extremes have intensified in Mahantango Creek, Pennsylvania. Scientific Reports. 14:27837. https://doi.org/10.1038/s41598-024-79196-3
DOI: https://doi.org/10.1038/s41598-024-79196-3

Interpretive Summary: Extreme rainfall is increasing with climate warming, and these rainfall extremes pose growing risks to agriculture. In this study, we used 55 years of 5-minute rainfall measurements to determine how 15-minute, hourly, and daily rainfall extremes were changing over time. We found that the magnitude and frequency of 15-minute rainfall extremes were increasing faster than hourly and daily extremes in the spring season. We also found evidence suggesting that warming temperatures in the spring had enhanced the environment for thunderstorm development, which could partly explain the faster rise in shorter duration rainfalls. Findings from the study have important implications for farming in a changing climate, as spring is an important season for field activities, including tilling, fertilization, and planting.

Technical Abstract: Extreme precipitation is intensifying with climate warming, and growing evidence suggests that subhourly rainfall extremes are increasing faster than more widely studied durations at hourly and daily timescales. In this study, we leveraged 55 years (1968–2022) of 5-min precipitation data from an experimental agricultural watershed in east-central Pennsylvania to examine annual and seasonal trends in the magnitude and frequency of subhourly (15-min), hourly, and daily rainfall extremes. We also determined how rainfall extremes scaled with dew point temperature, as such scaling indicated if extreme rains intensified with warming consistent with the Clausius-Clapeyron (CC) relation (' 7% per °C). Overall results showed that the most important trends in extreme precipitation happened at subhourly timescales during the spring. Trend tests revealed that the magnitude of 15-min rainfall extremes increased by 0.6 to 0.9% per year in the spring, while the frequency of these extremes also rose by 3.4% per year. Detailed analyses of scaling relations showed that springtime 15-min rainfall extremes shifted from sub-CC scaling at dew point temperatures below 11° C, to greater than 2CC scaling above this threshold. This relationship suggested a shift in the relative importance of stratiform versus convective rains in generating extreme 15-min rainfalls in the spring. Increasing trends in springtime CAPE alongside upward trends in indicator variables of convectively-triggered storms further supported the hypothesis that convective precipitation in the spring season was contributing more to 15-min rainfall extremes than it had in the past. Collectively, these findings show that 15-min rainfall extremes have intensified faster than hourly and daily extremes in the spring in the WE-38 watershed, which has important implications for agricultural management in a warming climate.