Climatological Reproducibility Evaluation and Future Climate Projection of Extreme Precipitation Events in the Baiu Season Using a High-Resolution Non-Hydrostatic RCM in Comparison with an AGCM

Abstract

This paper studies an evaluation of climatological reproducibility and one of future climate projections of extreme precipitation in the Baiu season (from mid-May to July) around Japan using data of numerical experiments. The models are a non-hydrostatic cloud-system-resolving atmospheric model with a horizontal grid size of 5 km (5km-NHM) utilized as a regional climate model (RCM), and an atmospheric general circulation model (AGCM) with a horizontal resolution of about 20 km (20km-AGCM) which provided the boundary condition of 5km-NHM. Ten-year runs were performed by the time-slice method. The mean precipitation amount of the three heaviest precipitation events that ranked in order of precipitation amount in every year (P Top3 ) at each grid point was used as an index to examine quantitatively extreme precipitation within a specific term with various precipitation accumulation periods (APs).The 5km-NHM experiment reproduced P Top3 much better than that of 20km-AGCM, especially for shorter APs. In the projection of P Top3 in the future climate with 5km-NHM, ratio in two climate states of P Top3 for longer APs and that of precipitation amount show the roughly same pattern. The increase areas of those were localized around Kyushu, Japan. In particular, the P Top3 for longer APs was projected to increase 30−70% in the mountainous areas along the Pacific coast of western Japan. This increase was due to a cyclonic circulation of an incremental low-pressure generated on the western side of Kyushu. On the other hand, large increases of P Top3 for shorter APs spread widely with a scattered pattern to the area where precipitation decreases. This characteristic was associated with the intensification of precipitation due to global warming.

Climatological Characteristics of Daily Precipitation over Japan in the Kakushin Regional Climate Experiments Using a Non-Hydrostatic 5-km-Mesh Model: Comparison with an Outer Global 20-km-Mesh Atmospheric Climate Model

“…Figure 4 shows the horizontal distribution of the mean topthree daily precipitation amounts in APHRODITE, AGCM20km, and NHM5km, which are averaged from the three largest daily precipitation amounts among the grids of AGCM20km from June to October for a 10-year period (1990−1999). A similar index (PTOP3) is proposed by Wakazuki et al (2008). In APHRODITE, regions with daily precipitation amounts above 200 mm day −1 are located on the Pacific side of the Japanese Islands south of 37°N, and regions exceeding 300 mm day −1 are found south of 35°N.…”

“…Even a super-fine global 20-km-mesh atmospheric climate model (AGCM20km) underestimates intense precipitation over Japan, although temperature extremes are well represented (Mizuta et al 2005). On the other hand, Wakazuki et al (2008) showed a finer-mesh model with a horizontal resolution of 5 km can reproduce intense precipitation during the Baiu season (June and July) by using the results of regional climate experiments of the Kyousei Project (Yoshizaki et al 2005), which was the forerunner of the Kakushin Program (Kitoh et al 2009). In addition, Sasaki et al (2008) reported that a non-hydrostatic model with a horizontal resolution of 4 km performed well in reproducing the appearance frequency of intense precipitation.…”

Precipitation downscaling under climate change: Recent developments to bridge the gap between dynamical models and the end user

“… Hohenegger et al [2008] have shown that very high resolution (grid scale ≤5 km) climate modeling improves the diurnal cycle of convection. The representation of short‐duration precipitation extremes is also significantly improved at high resolution [ Wakazuki et al , 2008]. These resolutions are now common practice in numerical weather prediction [ Roberts and Lean , 2008] but are computationally very expensive and thus are currently limited to either short time periods or small spatial domains.…”

Realism of Rainfall in a Very High-Resolution Regional Climate Model

“…This is due to the improved representation of complex topography and land surface processes. Thus there are very few examples of such resolutions being applied in climate studies, and these are limited to small domains and often just the summer season (Hohenegger et al 2008;Wakazuki et al 2008;Knote et al 2010). At these resolutions models are termed ''convection permitting,'' as larger convective storms and mesoscale organization are permitted but convective plumes and smaller showers are still not resolved.…”