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.
Precipitation extremes on multiple timescales – Bartlett–Lewis rectangular pulse model and intensity–duration–frequency curves
