著者

Hirokazu Endo Akio Kitoh Hiroaki Ueda

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.57-63, 2018 (Released:2018-04-28)

参考文献数

39

被引用文献数

33

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Recent studies indicate that the view of a general weakening of the monsoon circulation in a warmer climate cannot be simply applied in the Asian monsoon regions. To understand the Asian summer monsoon response to global warming, idealized multi-model experiments are analyzed. In the coupled model response to increased CO2, monsoon westerlies in the lower troposphere are shifted poleward and slightly strengthened over land including South Asia and East Asia, while the tropical easterly jet in the upper troposphere are broadly weakened. The different circulation responses between the lower and upper troposphere is associated with vertically opposite changes in the meridional temperature gradient (MTG) between the Eurasian continent and the tropical Indian Ocean, with a strengthening (weakening) in the lower (upper) troposphere. Atmospheric model experiments to separate the effects of CO2 radiative forcing and sea surface temperature warming reveal that the strengthened MTG in the lower troposphere is explained by the CO2 forcing. On a global perspective, CO2-induced enhancement of the land–sea thermal contrast and resultant circulation changes are the most influential in the South Asian monsoon. This study emphasizes an important role of the land warming on the Asian monsoon response to global warming.

著者

Tetsuya Kawano Ryuichi Kawamura

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.1-5, 2018 (Released:2018-01-18)

参考文献数

21

被引用文献数

5

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To investigate the influence of the distribution of sea ice in the Sea of Okhotsk on the behavior of a severe snowstorm, which occurred in Hokkaido, Japan, on 2 March 2013 and which was associated with an explosive cyclone, three WRF simulations with realistic, reduced, and enhanced sea ice-cover were carried out. A comparison among these experiments reveals that the extent of the sea ice influenced low-level temperatures and winds to the rear of the cyclone center during the development of the explosive cyclone over the Sea of Okhotsk. Sea ice insulates the ocean from heat exchange with the atmosphere. As a result, when the Okhotsk sea ice extent reaches Hokkaido Island, cold air masses from the north traverse the island without first being heated by the ocean. The consequent temperature reduction produces a low-level higher pressure region to the rear of the cyclone center. As a result, a large geopotential gradient is generated just to the rear of the cyclone center, and low-level winds are intensified within this region. Therefore, the Okhotsk sea ice extent reaching Hokkaido Island plays a significant role in lowering temperatures and intensifying winds in the island.

著者

Nobuyuki Kayaba Takashi Yamada Syugo Hayashi Kazutoshi Onogi Shinya Kobayashi Koichi Yoshimoto Kenji Kamiguchi Kazuya Yamashita

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.12, pp.1-5, 2016 (Released:2016-01-20)

参考文献数

8

被引用文献数

28

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The Japan Meteorological Agency (JMA) completed its second global atmospheric reanalysis, the Japanese 55-year Reanalysis (JRA-55). However, the horizontal spatial resolution of JRA-55, TL319 (about 55 km), is insufficient for representing the hilly topography of the Japanese islands. Therefore, to reproduce extreme events caused by the hilly topography and their long-term climatological change in Japan, JMA has conducted a dynamical regional downscaling, called DSJRA-55, based on JMA's operational mesoscale model, which has a horizontal resolution of 5 km. DSJRA-55 receives its initial field and boundary conditions from the JRA-55 reanalysis. DSJRA-55 is historically the first products in the world that covers very long term for 55 years with very high resolution in 5 km. Furthermore, DSJRA-55 does not perform data assimilation; instead, initial field and boundary conditions are given at frequent intervals to the downscaled model and short-range forecasts are performed. Then, successive forecasts are connected continuously to create the DSJRA-55 product. In early evaluation results, DSJRA-55 was able to reproduce observed temperature and precipitation during 1958-2012. Although it showed a systematic temperature bias in some regions and seasons and it underestimated the frequencies of heavy-rain days and heavy-rain hours, DSJRA-55 reproduced the overall distribution of orographic precipitation well. DSJRA-55 is therefore expected to be useful for analyzing past extreme events and for statistical studies of long-term climate.

著者

Miki Hattori Jun Matsumoto Shin-Ya Ogino Takeshi Enomoto Takemasa Miyoshi

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.12, pp.75-79, 2016 (Released:2016-03-08)

参考文献数

17

被引用文献数

7

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The impact of additional radiosonde observations during the Vietnam-Philippines Rainfall Experiment 2010 (VPREX2010) was investigated by performing observing system experiments using the local ensemble transform Kalman filter (LETKF) and the atmospheric general circulation model for the Earth Simulator (AFES). During the experimental period from 15 September to 15 October, 2010, a westward-propagating disturbance was developed in the South China Sea and caused heavy rainfall on the east coast of Vietnam and Hainan Island. By assimilating the additional radiosondes, significant increases in wind speed, temperature and specific humidity were detected in the lower troposphere around the disturbance. In addition, the analysis ensemble spread for meridional wind decreased by 5-25% across the Indochina Peninsula, Philippines Sea and western Pacific to the south of Japan. Moreover, winds became stronger around the disturbance due to the additional observations, and the ensemble spread for wind speed became larger. The results show that the disturbance in an early stage of development was not well detected in the South China Sea without the use of additional radiosonde observations. Therefore, it is suggested that continuous and intensive radiosonde observations in Vietnam and the Philippines are essential for the improvement of the objective analysis of such disturbances.

著者

Masashi Kohma Kaoru Sato

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.9, pp.9-14, 2013 (Released:2013-02-02)

参考文献数

27

被引用文献数

1

---

It is shown that there are two types of wave solutions trapped at the boundaries which owe to the Coriolis force proportional to the meridional component of the earth's rotation vector (hereafter referred to as the fH force) under the nontraditional approximation (non-TA). One is a type of Kelvin waves (non-TA Kelvin waves) trapped on the eastern and western boundaries. Unlike traditional Kelvin waves (TA Kelvin waves), non-TA Kelvin waves trapped on the western (eastern) boundary can have northward (southward) phase and group velocities in the Northern Hemisphere (NH). The other is a type of Rossby waves trapped on the ground. The external Rossby waves can have wave structure in the vertical and amplitudes decaying with height. Moreover, the fH force modifies even the characteristics of TA Kelvin waves trapped on the southern and northern boundaries: In the NH, the Kelvin waves trapped on the southern boundary have an upper limit (kc) to the zonal wavenumber (k), and those with large k (> kc) trapped on the northern boundary have eastward phase velocity in the NH. The latter is regarded as the third type of edge waves unique to non-TA.

著者

Kentaro Araki Hiroshi Ishimoto Masataka Murakami Takuya Tajiri

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.10, pp.57-61, 2014 (Released:2014-04-24)

参考文献数

20

被引用文献数

1 3

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We examined proximity soundings at intervals of a few minutes and at distances of less than 20 km from a significant tornadic (SIGTOR) supercell that occurred on 6 May 2012 in Japan. We used a 1-dimensional variational (1DVAR) technique that combined the observations of a ground-based microwave radiometer with outputs from a numerical model. Based on the results of the 1DVAR, several supercell and tornado forecast parameters were calculated and compared with values typical of SIGTOR supercell environments in the United States. One and a half hours before the occurrence of the tornado, the value of convective available potential energy increased significantly to about 1000 J kg−1, a value that is smaller than the typical value in the United States. Low-level vertical wind shear and some composite parameters attained maximum values at the time when the distance to the supercell was the smallest. The vertical wind shear parameters and some composite parameters indicated that the environment fell into the SIGTOR supercell category. This result shows that the thermodynamic environments became unstable before the approach of the supercell, and the low-level vertical wind shear changed locally near the supercell.

著者

Takumi Matsunobu Julian F. Quinting Christian M. Grams Mio Matsueda

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.19, pp.253-260, 2023 (Released:2023-10-31)

参考文献数

35

---

The statistical and dynamical relationships between regional extreme precipitation events (EPEs) during wintertime in five Japanese regions and East-Asian synoptic weather patterns are addressed. Two of the five weather patterns, the southerly flow (SF) and low pressure (LP), are associated with about 50% of EPEs in all the regions. A regional dependency is found, with SF being more likely to cause extreme precipitation in two regions in the south of Japan and LP in the other regions, respectively. The large-scale dynamics leading to EPEs in each region are assessed by a combined Lagrangian and Eulerian analysis. In the two southern regions, EPEs are predominantly associated with direct moisture supply from the subtropical oceans. This is modulated by the large-scale flow pattern of SF. In contrast, EPEs in the northern coastal areas of the Sea of Japan and the Pacific Ocean are influenced by anomalous moisture supply from the cyclone-induced moisture convergence modulated by LP. The eastern coastal region of the Sea of Japan shows a mixture of both these moisture supply mechanisms. The strong link between EPEs and synoptic patterns might help to improve predictions of extreme events, even on the sub-seasonal forecast skill horizon.

著者

Shimizu Shingo

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.19A, no.Special_Edition, pp.i-iii, 2023 (Released:2023-10-24)

参考文献数

11

---

Catastrophic disasters triggered by mesoscale convective systems occur annually in East Asia, with a notable increase in casualties and extensive damages between 2019 and 2021 due to record-breaking rainfall in Japan. There is an urgent need for a comprehensive understanding of the physical processes and dynamic mechanisms behind these extreme rainfall events. This requires the integration of various research approaches, including observational analysis, statistical data analysis, and weather forecasting with data assimilation. Additionally, we must consider the impact of large-scale atmospheric circulation on extreme weather in East Asia. In this special edition, jointly coordinated with Journal of the Meteorological Society of Japan, we have published nine articles covering extreme events in East Asia from 2017 to 2022. Here, we provide an overview of these papers. From a large-scale view perspective, Horinouchi et al. (2021) and Ueda et al. (2021) examined the influence of synoptic-scale moisture conditions and sea surface temperatures on severe rainfall events in Kyushu, Japan during the summer of 2020. Additionally, Takemura et al. (2022) investigated the large-scale atmospheric factors contributing to the record-breaking early onset of Baiu season in most parts of western Japan in 2021. Furthermore, Kuramochi et al. (2021) conducted a study on the causes of the anomalous warm conditions in winter 2019 and 2020 over East Asia, utilizing large-scale atmospheric analysis and global simulations. Three papers focused on the statistical features of environmental conditions suitable for the occurrence of “senjo-kousuitai” (Kato 2020). Goto and Satoh (2022) applied a similar definition of senjo-kousuitai as proposed by Kato 2020 to a satellite-based precipitation dataset covering 20 years from 2000 to 2019. They confirmed a high occurrence frequency in Kyushu, the Nansei Islands (South of Kyushu), and the East China sea. Based on analysis using reanalysis datasets, it was determined that low-level water vapor flux and vertical wind shear are essential for the development of senjo-kousuitai. Sato and Hosotani (2023) also confirmed the importance of these two factors based on reanalysis data spanning the past 20 years. Additionally, Naka and Takemi (2023) proposed the significance of moist absolutely unstable layers (MAULs) in enhancing heavy rainfall in the preceding hours. Numerical simulations were also employed in research efforts. Tochimoto et al. (2022) conducted sensitivity experiments to investigate the impact of the upper-level trough on the heavy rainfall. In another study, Terasaki and Miyoshi (2022) demonstrated the high predictability of heavy rainfall by utilizing data assimilation with 1024-ensemble members. Doyle et al. (2023) indicated the importance of a mesoscale convective system, orographic ascent, and equatorial wave components in contributing to the extreme flood that occurred in southwestern Sulawesi, Indonesia in January 2019 by conducting adjoint model simulations and the sensitivity analysis. To mitigate the damages caused by various extreme weather events, it is essential to consolidate our research achievements and further enhance the predictability of these events.

著者

Kazuto Takemura Hitoshi Mukougawa Shuhei Maeda

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.125-129, 2021 (Released:2021-06-26)

参考文献数

18

被引用文献数

2

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Rossby waves propagating along the Asian jet frequently cause the breaking near the jet exit region. This study examines characteristics of oceanographic condition and atmospheric circulation associated with interdecadal variability of Rossby wave breaking frequency near Japan in August. Sea surface temperature during a period of the higher Rossby wave breaking frequency is cooler over the central part of the tropical North Pacific, compared with that during a period of the lower frequency. Convective activities are suppressed over the region consistent with the cooler sea surface temperature, contributing to an enhanced and southwestward extended mid-Pacific trough. Deceleration and diffluence of the Asian jet are stronger during the period of the higher frequency than that during the period of the lower one. The enhanced deceleration and diffluence of the jet are associated with the enhanced and southwestward extended mid-Pacific trough. The abovementioned dynamical influence is also shown by a numerical simulation using an atmospheric linear baroclinic model. These results indicate that the interdecadal variability of sea surface temperature over the central part of the tropical North Pacific has an impact on that of the Rossby wave breaking frequency near Japan, through the modulated convective activities and mid-Pacific trough.

著者

Takumi Matsunobu Julian F. Quinting Christian M. Grams Mio Matsueda

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2023-033, (Released:2023-09-16)

---

The statistical and dynamical relationships between regional extreme precipitation events (EPEs) during wintertime in five Japanese regions and East-Asian synoptic weather patterns are addressed. 4 Two of the five weather patterns, the southerly flow (SF) and low pressure (LP), are associated with about 50% of EPEs in all the regions. A regional dependency is found, with SF being more likely to cause extreme precipitation in two regions in the south of Japan and LP in the other regions, respectively. The large-scale dynamics leading to EPEs in each region are assessed by a combined Lagrangian and Eulerian analysis. In the two southern regions, EPEs are predominantly associated with direct moisture supply from the subtropical oceans. This is modulated by the large-scale flow pattern of SF. In contrast, EPEs in the northern coastal areas of the Sea of Japan and the Pacific Ocean are influenced by anomalous moisture supply from the cyclone-induced moisture convergence modulated by LP. The eastern coastal region of the Sea of Japan shows a mixture of both these moisture supply mechanisms. The strong link between EPEs and synoptic patterns might help to improve predictions of extreme events, even on the sub-seasonal forecast horizon.

著者

Mikio Nakanishi

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2023-018, (Released:2023-05-30)

被引用文献数

1

---

The Noah multi-parameterization (Noah-MP) scheme is one of several land surface schemes implemented in the Weather Research and Forecasting (WRF) model. Our simulations by the WRF model with the Noah-MP scheme show that surface air temperatures in the morning and evening tend to be higher and lower, respectively, than observed, and that the temperatures at an urban station with snow cover increase little from 0 ℃ even in the daytime. The former depends on surface energy balance in the skin layer and the latter results from snow cover assumed to be uniform over a grid cell. These weaknesses are improved by considering the partial transmission of the solar radiation through the skin layer to the soil layer, the heat capacity of the vegetation canopy, and a mixture of soil layers with and without snow cover. The present scheme will contribute to an improvement of the Noah-MP scheme.

著者

Biao Geng

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2023-017, (Released:2023-05-24)

---

This study investigated the internal precipitation and kinematic structure of the South Pacific convergence zone (SPCZ) observed by the Doppler radar aboard the research vessel Mirai, which passed through the western tropical portion of the SPCZ on December 17-21, 2016. Convective precipitation developed in association with the low-level convergence induced by the monsoon and the upper-level divergence associated with extratropical Rossby wave breaking. Mesoscale convective systems (MCSs) developed from either intersecting (northeast–southwest/northwest–southeast) or zonally oriented convective bands. For the MCS developing from the former mode, the zonal and meridional divergence fields made comparable contributions to convective development. For the MCS developing from the latter mode, the divergence field induced by the meridional wind had the largest contribution to producing convection. The MCS with stronger convective updrafts and higher echo tops and coverage occurred in the region where more intense convergence was observed near the surface. The results of this study highlight the dependence of organizational modes of SPCZ convection on the coupling of the tropical low-level and extratropical upper-level forcings, as well as on the zonal and meridional forcing structures.

著者

Soichiro Hirano Kosuke Ito Hiroyuki Yamada

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2023-015, (Released:2023-05-16)

---

In the western North Pacific, as a tropical cyclone (TC) translates northward and approaches the midlatitude jet region, a front is often observed to the northeast of the TC, especially in fall. Theoretically, a front accompanies positive vorticity in the lower troposphere because convergence of cross-frontal circulation generates positive vorticity. Horizontal winds accompanied by positive vorticity along a front can impact the TC track. This study estimates the influence of frontal positive potential vorticity (PV) on the TC track using reanalysis data for a case of TC Chan-hom (2020). Horizontal winds due to frontal PV (FPV) are calculated using PV inversion. The FPV produces west-southwesterlies around the TC center just after the FPV formation. Thereafter, it mainly produces northwesterlies. Steering flow due to the FPV displaces Chan-hom 50 km east-southeastward for 72 h.

著者

Ken Hirata Miho Sekiguchi Yousuke Sato Masaru Inatsu

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.19, pp.50-56, 2023 (Released:2023-03-23)

参考文献数

22

---

This study investigated biases of diffuse radiation in a look-up table approach, which pre-computed the sequential ray tracing to avoid heavy computation in full three-dimensional radiative transfer calculation. We introduced corrections that enhanced directionality of radiative propagation in the solar angle and horizontal direction. By comparing irradiance calculations with and without the corrections for cloudy field in an idealized atmospheric simulation, it was found that the corrections helped mitigate vertically localized false signals by diffuse irradiance. The results suggested that the two types of directionalities are important to accurately represent the three-dimensional transfer of diffuse radiation in an inhomogeneous atmosphere.

著者

Yu Matsumoto Minrui Wang Yousuke Sato Takashi Y. Nakajima

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2023-009, (Released:2023-03-14)

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This paper shows the CFODD of the regional dependence of cloud growth processes in low-level clouds obtained by the combined use of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite and the Cloud Profiling Radar (CPR) on the CloudSat satellite. This enabled the evaluation of the cloud growth process based on the cloud optical thickness (τ) and the effective radius of cloud particle (Re), similar to previous studies that performed statical analysis on low-level clouds over the globe. Our targets were regions in East Asian, Californian, and Peruvian. In all analysis areas, our results showed that the internal structure of clouds changed as Re increased, indicating cloud growth. In the East Asian region, the maximum τ remained relatively constant even when cloud droplet size grew. In contrast, in the regions of Californian and Peruvian, the maximum τ increased with Re during the condensation growth process and then decreased as drizzle particles transformed into rain. It was also found that Re was smaller in the East Asian region unlike in Californian and Peruvian. This indicates that there are more aerosols in the East Asian region, which is consistent with its geographical characteristics.

著者

Yang Zhao Seok-Woo Son Seung-Yoon Back

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.19, pp.42-49, 2023 (Released:2023-03-04)

参考文献数

25

被引用文献数

2

---

On 18-20 July 2021, Henan Province in China experienced a historically rare extreme precipitation event, termed as the “21.7” event. Its synoptic environment was characterized by a large amount of moisture supply by binary typhoons located over the ocean and a potential vorticity intrusion in the upper level. The present study examines the importance of the latter by conducting WRF model experiments. A qualitatively similar rainfall amount to observation is obtained when the zonal wavenumber 7 and larger is kept above 300 hPa in the initial and lateral boundary conditions. When only the large-scale disturbances with wavenumbers 2-4 are kept, the precipitation is greatly reduced. This result indicates that the upper-level synoptic-scale disturbance, which leads to the development of potential vorticity anomaly and its downward intrusion, has likely played a critical role in the development of this event along with a large amount of moisture transport in the low level.

著者

Ken Hirata Miho Sekiguchi Yousuke Sato Masaru Inatsu

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2023-007, (Released:2023-01-30)

---

This study investigated biases of diffuse radiation in a look-up table approach, which pre-computed the sequential ray tracing to avoid heavy computation in full three-dimensional radiative transfer calculation. We introduced corrections that enhanced directionality of radiative propagation in the solar angle and horizontal direction. By comparing irradiance calculations with and without the corrections for cloudy field in an idealized atmospheric simulation, it was found that the corrections helped mitigate vertically localized false signals by diffuse irradiance. The results suggested that the two types of directionalities are important to accurately represent the three-dimensional transfer of diffuse radiation in an inhomogeneous atmosphere.

著者

Hidetaka Sasaki Noriko N. Ishizaki Akihiko Murata Hiroaki Kawase Masaya Nosaka

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.19, pp.9-15, 2023 (Released:2023-01-12)

参考文献数

16

被引用文献数

1

---

The surface temperature was projected to increase from 4 to 5°C in most regions around Japan in winter at the end of the 21st century, according to the Non-Hydrostatic Regional Climate Model (NHRCM) under the Representative Concentration Pathway 8.5 scenario. The melting of sea ice in the Sea of Okhotsk significantly affected the temperature around Hokkaido Prefecture, raising it by more than 8°C in some places. The temperature also rose by more than 8°C in some areas in Honshu where the atmosphere was not susceptible to sea ice. The reduction in snow-covered areas due to global warming raised the temperature further and induced changes in local wind, such as airflows over mountains and wind blowing from the sea. These changes raised the seasonal average temperature and caused the temperature to rise by over 8°C. The dynamical downscaling method played a significant role in projecting such small-scale features in the future climate.

著者

Yuka Kanamori Masaru Inatsu Ryoichi Tsurumaki Naoki Matsuoka Tsuyoshi Hoshino Tomohito J. Yamada

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.249-253, 2022 (Released:2022-11-26)

参考文献数

23

被引用文献数

1

---

A set of hydrological experiments for a flooding event on 11 September 2014 at Motsukisamu River in Sapporo were performed. Dynamical downscaling to 5-km resolution of a large-ensemble global simulation allowed us to estimate that a 99%-tile hourly precipitation in Sapporo would increase by 70% in a future climate, when the global-mean temperature increases by 4 K compared with the present climate. After developing a three-tank model of which parameters were optimized on the basis of the in-situ observation at the Motsukisamu River during the event period, the model was forced by hypothetical hyetographs of the event that would occur under the future climate. The results of this experiment suggested that the peak flow rate would increase by 75%. However, it was also revealed that an upstream aqueduct tunnel, just completed in autumn 2021, would effectively reduce the peak flow rate and mitigate the flooding risk even in extreme precipitation under the future climate.

著者

Yuka Kanamori Masaru Inatsu Ryoichi Tsurumaki Naoki Matsuoka Tsuyoshi Hoshino Tomohito J. Yamada

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-040, (Released:2022-11-11)

被引用文献数

1

---

A set of hydrological experiments for a flooding event on September 11, 2014 at Motsukisamu River in Sapporo were performed. Dynamical downscaling to 5-km resolution of a large-ensemble global simulation allowed us to estimate that a 99%-tile hourly precipitation in Sapporo would increase by 70% in a future climate, when the global-mean temperature increases by 4 K compared with the present climate. After developing a three-tank model of which parameters were optimized on the basis of the in-situ observation at the Motsukisamu River during the event period, the model was forced by hypothetical hyetographs of the event that would occur under the future climate. The results of this experiment suggested that the peak flow rate would increase by 75%. However, it was also revealed that an upstream aqueduct tunnel, just completed in autumn 2021, would effectively reduce the peak flow rate and mitigate the flooding risk even in extreme precipitation under the future climate.