The Emergence of a Climate Change Signal in Ireland’s Rainfall Extremes

Detecting the emergence of anthropogenic climate change signals in precipitation is essential for informing adaptation strategies. This study analyses long-term, quality-assured observations from 36 stations across Ireland (1930–2019) to assess trends and emergence in six seasonal precipitation indices. Using a combination of Mann-Kendall trend testing, Theil-Sen slope estimation, and monthly persistence analysis, robust seasonal changes are identified. Emergence is evaluated by regressing local precipitation indices against global mean surface temperature (GMST), with the resulting signal to-noise ratio (SNR) classified as normal, unusual, or unfamiliar relative to early industrial (1850-1900) and modern (1950-1980) baselines. The influence of the North Atlantic Oscillation (NAO) is also assessed using commonality analysis. Results show statistically significant intensification of rainfall extremes, particularly in western Ireland during winter and spring, and in the southeast during summer and autumn. Many stations exhibit significant relationships with GMST, with increases in extreme indices (e.g., Rx5day, SDII) ranging from 12% to 27% per °C of warming, often exceeding thermodynamic expectations. Emergence of unusual climate conditions is already evident at several stations relative to the early industrial baseline, and many are nearing this threshold for the modern baseline. While NAO variability strongly modulates winter precipitation extremes in the west, significant GMST relationships in the SNR analysis indicate that these are still robust climate change signals. Commonality analysis reveals that GMST and NAO jointly explain variability in winter PRCPTOT and Rx5day at western stations, suggesting that natural modes of variability like the NAO may not be independent noise but rather embedded within a warming climate signal, complicating the separation of anthropogenic and natural drivers in attribution studies. Findings also challenge projections of widespread summer drying with warming, instead revealing intensification of short duration extremes in the southeast. As Ireland faces increasingly intense and seasonally variable rainfall extremes, these results highlight the urgency of regionally tailored adaptation strategies grounded in observed climate change signals. These results provide robust observational indications of an intensifying atmospheric water cycle and emerging precipitation extremes over Ireland under anthropogenic warming.