Projected intensification of sub-daily and daily rainfall extremes in convection-permitting climate model simulations over North America: implications for future intensity–duration–frequency curves

Abstract

Abstract. Convection-permitting climate models have been recommended for use in projecting future changes in local-scale, short-duration rainfall extremes that are of the greatest relevance to engineering and infrastructure design, e.g., as commonly summarized in intensity–duration–frequency (IDF) curves. Based on thermodynamic arguments, it is expected that rainfall extremes will become more intense in the future. Recent evidence also suggests that shorter-duration extremes may intensify more than longer durations and that changes may depend on event rarity. Based on these general trends, will IDF curves shift upward and steepen under global warming? Will long-return-period extremes experience greater intensification than more common events? Projected changes in IDF curve characteristics are assessed based on sub-daily and daily outputs from historical and late 21st century pseudo-global-warming convection-permitting climate model simulations over North America. To make more efficient use of the short model integrations, a parsimonious generalized extreme value simple scaling (GEVSS) model is used to estimate historical and future IDF curves (1 to 24 h durations). Simulated historical sub-daily rainfall extremes are first evaluated against in situ observations and compared with two high-resolution observationally constrained gridded products. The climate model performs well, matching or exceeding performance of the gridded datasets. Next, inferences about future changes in GEVSS parameters are made using a Bayesian false discovery rate approach. Large portions of the domain experience significant increases in GEVSS location (>99 % of grid points), scale (>88 %), and scaling exponent (>39 %) parameters, whereas almost no significant decreases are projected to occur (<1 %, <5 %, and <5 % respectively). The result is that IDF curves tend to shift upward (increases in location and scale), and, with the exception of the eastern US, steepen (increases in scaling exponent), which leads to the largest increases in return levels for short-duration extremes. The projected increase in the GEVSS scaling exponent calls into question stationarity assumptions that form the basis for existing IDF curve projections that rely exclusively on simulations at the daily timescale. When changes in return levels are scaled according to local temperature change, median scaling rates, e.g., for the 10-year return level, are consistent with the Clausius–Clapeyron (CC) relation at 1 to 6 h durations, with sub-CC scaling at longer durations and modest super-CC scaling at sub-hourly durations. Further, spatially coherent but small increases in dispersion – the ratio of scale and location parameters – of the GEVSS distribution are found over more than half of the domain, providing some evidence for return period dependence of future changes in extreme rainfall.

Projected Changes in the Probability Distributions, Seasonality, and Spatiotemporal Scaling of Daily and Subdaily Extreme Precipitation Simulated by a 50‐Member Ensemble Over Northeastern North America

“…This indicates that the changes of point‐scale AM quantiles across durations are expected to be larger in future climate than those observed in past periods. Similar results were also obtained in previous studies (e.g., and references therein Cannon & Innocenti, ), which reported an increase in time of SS exponents for rainfall intensity distributions or, equivalently, decreasingly negative slopes of IDF curves in future climate. Note, in fact, that point scale IDF slopes can be expressed as , where is the temporal scaling parameters for AM precipitation intensity.…”

“…Finally, it can be noted that grid point trends for were larger than corresponding trends in some areas (e.g., over the Great Lakes region for SD; Figure jgrd55749-fig-0012a). Standardized measures of AM distribution dispersion, such as the normalized dispersion coefficient , are thus expected to increase in time over these regions, as suggested by Cannon and Innocenti (2019). In fact, significant trends of the normalized dispersion coefficients were observed for a large majority of grid boxes (e.g., Figure S9 in the supporting information).…”

“…As a result, the future evolution of the extreme precipitation spatiotemporal structure simulated by the CRCM5 can be assessed through the projected h 0, t and h 1, t values. For instance, previous studies stressed that temporal scaling parameters might change with time, questioning the adequacy of stationary frameworks classically used to estimate DDF and IDF slopes (e.g., Casas‐Castillo et al., for observed rainfall extremes; Cannon & Innocenti, for daily and subdaily simulated AM). Finally, note that some authors underlined the presence of two temporal scaling regimes for short (e.g., hourly and subhourly) and long (e.g., daily and longer) durations (e.g., Ceresetti, ; Eggert et al., ).…”

Seasonality, Intensity, and Duration of Rainfall Extremes Change in a Warmer Climate

“…Our results add to the wide scientific consensus toward rainfall intensification (Westra et al, 2014) and confirm previous findings that suggest an intensification throughout the US (Bador et al, 2018;Barbero et al, 2019;Cannon & Innocenti, 2019;Easterling et al, 2017;Fischer et al, 2013;Pfahl et al, 2017;Prein, Liu, Ikeda, Trier, et al, 2017;. A similar decrease in PEx seasonality has only recently been demonstrated over Europe based on continental-wide CPM future projections (Chan et al, 2020).…”

Investigation of Trends, Temporal Changes in Intensity-Duration-Frequency (IDF) Curves and Extreme Rainfall Events Clustering at Regional Scale Using 5 min Rainfall Data

“…Firstly, extreme rainfall amounts for short durations, such as 5 min or 30 min, are increasing and thus have an impact on the constructed IDF curves. This hypothesis could be determined based on the climate change impact that is expected to lead to an increased frequency of extreme events (e.g., [2,12]). Secondly, extreme events at the regional scale (approx.…”