Future Projections of Extreme Ocean Wave Climates and the Relation to Tropical Cyclones: Ensemble Experiments of MRI-AGCM3.2H*

Abstract

Future projections of extreme ocean surface wave climates were carried out with single-model ensemble experiments of the atmospheric global climate model MRI-AGCM3.2H. The ensemble experiments of MRI-AGCM3.2H consist of four future sea surface temperature (SST) ensembles and three perturbed physics (PP) ensembles. This study showed that future changes in extreme wave heights strongly depend on the global climate model (GCM) performance to simulate tropical cyclones (TCs), indicating a need to acknowledge that results in a study that employs a low-performance model are not able to account for extreme waves associated with TCs (TC waves). The spatial distribution of future changes in non-TC extreme wave heights on the global scale was similar to that for mean wave heights; namely, wave heights increase over the middleto-high latitudes in the Southern Ocean and central North Pacific and decrease over midlatitudes and the North Atlantic, although the magnitude of future changes for extreme wave heights is greater than for mean wave heights. The variance of future changes mainly depends on differences in physics among PP ensemble experiments rather than differences in SST ensembles. The 10-yr return wave heights of TC waves over the western North Pacific showed either an increase or a decrease of 30% for different regions, maximally. The spatial distribution of future changes in TC waves can be explained by an eastward shift of TC tracks.

Impact of tropical cyclones on modeled extreme wind‐wave climate

“…Making a qualitative comparison with our results, the most dramatic future change we identify is the strengthening of TC waves west of Mexico, seen clearly in Figure c. Similar spatial patterns are exhibited by individual ensemble members shown in both Shimura et al [] and Fan et al [], Figure 5(l) and figure 8(h), respectively. However, variability between members suggests that wave climate reflects strongly the characteristics of the atmospheric forcing (influenced by SST patterns and model physics), and it remains unclear whether the features of our atmospheric data set, that manifest strongly in the extreme wave climate, are significant.…”

“…Recent studies that examine projections of extreme waves highlight the importance of other sources of uncertainty. Shimura et al [] and Fan et al [] focus on future changes in wave climate by considering the IPCC A1B scenario (comparable to RCP 8.5) at the end of the 21st century. Although different methodologies were employed, in both cases ensembles of global wave climatologies were generated numerically from forcing winds at resolutions of approximately 0.5°, which can produce TCs.…”

“…Downscaling approaches from historical and reanalysis data are also used [ Camus et al , ]. Environmental and societal impacts of weather and climate are typically associated with the largest magnitude events—the extremes—and a number of studies have considered the extremes of wave climate [ Wang et al , ; Mori et al , ; Shimura et al , ]. However, investigation of extremes through numerical modeling is challenging.…”

“…With more recent availability of sufficient computing resource to simulate climate at higher resolution, detailed investigation of TC climatology is possible [ Strachan et al , ; Murakami et al , ]. Consequently, studies of wind‐wave climate that capture more explicitly the effects of TCs are also appearing in the literature [ Fan et al , ; Shimura et al , ]. However, with a sparsity of research in this area, and studies employing different approaches, sources of uncertainty and their importance remain poorly understood.…”

Regime shifts in the multi‐annual evolution of a sandy beach profile

“…(). In eastern Japan including the study area, extreme waves are expected to increase in height in the coming decades mainly because of the eastward shift of tropical cyclone track due to climate change (Mori et al ., ; Shimura et al ., ). Winter storms over the North Atlantic and western Europe, one of which caused the extraordinarily large morphological change along the Atlantic coast of Europe in 2013/2014 winter (Masselink et al ., ), are expected to be intensified (Feser et al ., ).…”