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Climate-sensitive diseases developing from heat or cold stress threaten human health. Therefore, the future health risk induced by climate change and aging societies worldwide should be assessed. In this study, we developed the prediction model for mortality of cardiovascular diseases such as myocardial infarction and cerebral infarction, which are known weather- or climate-sensitive diseases, using machine learning techniques. We targeted daily mortality of ischaemic heart disease (IHD) and cerebrovascular disease in the 23 wards of Tokyo and in Osaka City, Japan during summer. The significance of delayed effects of daily maximum temperature and other weather elements on mortality was previously demonstrated using a distributed lag nonlinear model. We conducted machine learning (ML) including specified lag days, with important features of several temperature-related elements and air pressure-related elements for the mortality risk of IHD and cerebrovascular disease during the previous summers, respectively. These models, learned the past data, were used to evaluate the future risk of IHD mortality in Tokyo’s 23 wards owing to climate change by applying transfer learning architecture (TL). The ML incorporating TL predicted that the daily IHD mortality risk in Tokyo was averagely increased 29% and 35% at the 95th and 99th percentiles using a high-level warming climate scenario in 2045–2055, compared to the risk simulated using ML in 2009–2019.

We investigated decadal (2010–2019) cardiovascular, cerebrovascular, and respiratory mortality sensitivity to annual warm temperatures in major Japanese cities: Sapporo, Tokyo (23 wards), and Osaka. The summer mortalities (June–August) increased with the monthly mean temperature for acute myocardial infarction, other acute ischemic heart diseases, cerebral infarction, and pneumonia in the three cities. Monthly mean temperatures were an indicator of these disease mortalities in Japan. However, similar responses were not found for cardiac arrhythmia and heart failure (excluding Sapporo), subarachnoid hemorrhage, and intracerebral hemorrhage. The decadal sensitivities and risk ratios between the maximum and minimum monthly mean temperatures were calculated using a linear regression model. In Sapporo, Tokyo, and Osaka, for example, the analyses of acute myocardial infarction showed summer positive responses of 0.19–0.25, 0.13–0.18, and 0.12–0.30, respectively, as the mortality rate (per 100,000 population) per 1 °C of monthly mean temperature, which estimated increased risks (between the coolest and hottest months) of 37–65% in Sapporo, 31–42% in Tokyo, and 35–39% in Osaka.

The present study focussed on the formation of upslope fog. This fog causes chronic expressway closures near Beppu Bay (BB) in Oita Prefecture, Japan. A dense fog event, occurring on 3 and 4 May 2020, resulting from the passage of an extratropical cyclone through the southern Japanese islands, was simulated using the Weather Research and Forecasting (WRF) numerical model. The simulation results indicated that warm and humid air with a lifting condensation level less than 20 m flowed into a plain from BB. Simulated fog and poor visibility were more severe on mountain slope adjacent to BB than on the surroundings. Here, the westward horizontal flux of water vapour by the wind flow was prolonged at lower heights. Analyses of the simulated elements verified that the upslope fog was induced by moist adiabatic cooling of the air lifted by the upslope winds. At the mature stage of upslope fog, a simulated local vertical circulation generated in conjunction with the upper synoptic flow extended the dense fog into the upper atmosphere over BB. During the decaying stage of upslope fog on mountain, a fog covered on the entire BB. This was associated with weakening winds at lower heights. Sensitivity experiments for model boundary conditions supported the importance of mountain steepness and the rectangular shape of BB for the generation of upslope fog. Finally, an application possibility of dense fog forecasts was discussed by using a simulated difference in the equivalent potential temperature between the base of the mountain and Beppuwan expressway interchange located midslope.

To numerically assess winter cold damages of citrus fruits, a cold duration of sub-zero temperature was simulated using a high resolution configuration (500 m horizontal grid spacing) of the WRF numerical weather prediction system. Japanese citrus is often cultivated on slopes made of a small hill and a valley. Hence, a high resolution spatial configuration is needed to simulate cold durations at complex micro-topographies. In this study, detailed cold duration maps for sub-zero temperatures were produced to assess the spatial difference of cold duration, as an example of a winter cold surge attack in west Japan in 2011. Our findings suggest that the recorded temperature (by automatic observation of the Japan Meteorological Agency), which was observed at a flat coastal plain, may underestimate cold damage risk for citrus fruit on narrow slopes, valleys and hilly areas.

In this study, we validated urban air temperature and electricity demand by a year-round numerical simulation using a regional climate model coupled with an urban canopy model and a building energy model (RCM-UCM+BEM) in the Asian megacity, Osaka, which is the largest metropolis in Japan after Tokyo. The control simulation (CTRL), which was based on the use of central air-conditioning (AC) systems, reproduced the surface air temperatures observed in Osaka City in the summer cooling and interim seasons, but underestimated midnight to morning temperatures by over 2 °C in the winter heating season. In addition, the CTRL significantly overestimated the electricity demand in Osaka City in both the cooling and heating seasons, when the AC load was increased. These errors were likely due to the overestimation of AC use in the CTRL model because, in Japan, central AC systems are not used in business and residential areas, where individual AC units are mainly used. To prevent this overestimation, we introduced three new parameters to consider the use of partial AC systems in the model. The results of the new numerical experiment remarkably reduced the underestimation of temperature and the overestimation of electricity demand. This suggests that the RCM-UCM+BEM modified by this study is effective for not only reproducing the current status of seasonal urban air temperature and electricity demand in Osaka, but also for projecting the future situation in other mega cities.

In this study, the summertime outdoor heat stress hazard and heat disorder risk (HDR) were simulated, and their changes under several heat island mitigation scenarios were quantitatively evaluated. Gridded maps that included the 23 wards of Tokyo (23 Tokyo) were produced with 1-km horizontal resolution for consecutive summer months, facing extremely hot weathers, in 2010. The wet-bulb globe temperature (WBGT) was adopted as an outdoor heat stress indicator. Numerical simulations were applied to evaluate the effects of several heat island mitigation scenarios—including building greening (GR), high-albedo coating (ALB), and roof-level emissions of all waste heat by air conditioning (WH)—on the WBGT and HDR for 23 Tokyo. Results showed no cases that effectively lowered the outdoor WBGT and HDR for the studied region. Conversely, the ALB case increased the daily maximum WBGT by an average of 0.6 °C (maximum of 1.7 °C) over all the grids. This increase induced a 1.4 (3.3) times higher HDR in the area average (at the maximum grid) compared to a control case with no mitigation scenario. Hence, heat island mitigation methods reflecting solar radiation could potentially lead to an increase in the outdoor heat stress hazard and risk to a large extent in urban areas.

We investigated the cold stress caused by a strong local wind called “Hijikawa-arashi,” through in situ vital measurements and the Universal Thermal Climate Index (UTCI). This wind is a very interesting winter phenomenon, localized in an area within 1 km of the seashore in Ozu City, Ehime Prefecture in Japan. When a strong Hijikawa-arashi (HA) occurred at 14–15 m s−1, the UTCI decreased to − 30 °C along the bridge where commuting residents are the most exposed to strong and cold winds. On the bridge, most participants in our experiment felt “very cold” or “extremely cold.” The UTCI of HA can be predicted from a multiple regression equation using wind speed and air temperature. The cold HA wind is also harmful to human thermo-physiological responses. It leads to higher blood pressure and increased heart rate, both of which act as cardiovascular stress triggers. Increases of 6–10 mmHg and 3–6 bpm for every 10 °C reduction in UTCI were seen on all observational days, including HA and non-HA days. In fact, the participants’ body skin temperatures decreased by approximately 1.2 to 1.7 °C for every 10 °C reduction in UTCI. Thus, the UTCI variation due to the HA outbreak corresponded well with the cold sensation and thermo-physiological responses in humans. This result suggests that daily UTCI monitoring enables the prediction of thermo-physiological responses to the HA cold stress.

Future heat stress under six future global warming (ΔT GW ) scenarios (IPCC RCP8.5) in an Asian megacity (Osaka) is estimated using a regional climate model with an urban canopy and air-conditioning (AC). An urban heat ‘stress’ island is projected in all six scenarios (ΔT GW = +0.5 to +3.0 °C in 0.5 °C steps). Under ΔT GW = +3.0 °C conditions, people outdoors experience ‘extreme’ heat stress, which could result in dangerously high increases in human body core temperature. AC-induced feedback increases heat stress roughly linearly as ΔT GW increases, reaching 0.6 °C (or 12% of the heat stress increase). As this increase is similar to current possible heat island mitigation techniques, this feedback needs to be considered in urban climate projections, especially where AC use is large.

In this study, the summertime outdoor heat stress hazard and heat disorder risks (HDR) were simulated numerically using a mesoscale meteorological model combined with an urban canopy model and a building energy model. Model grid maps including the 23 wards of Tokyo (23 Tokyo), Japan, were produced with a 1-km horizontal resolution for the period of July–September 2010. Model simulations of the daily maximum wet-bulb globe temperature (WBGTmax), which was adopted as a heat stress index, indicated the spatial heterogeneity of the heat stress hazard within 23 Tokyo. The heat stress hazard was greater in the inland western region, particularly for sunny conditions in July and August (based on the monthly mean; the maximum difference exceeded 2°C for both sunny and shaded conditions). This likely occurred as a result of greater spatial heterogeneity in the globe temperature than in the air temperature among model grid cells, with differences in the radiation environment induced by differences in urban geometric parameters. Gridded mapping of HDR simulations proceeded in two steps, using the incidence rate and the absolute number of heat disorder patients (HDP). These simulations were achieved by combining the exponential relationships between the actual WBGTmax and the number of HDP with the daytime grid population. Eventually, the resulting HDR maps incorporated the effects of the spatial heterogeneities of both the outdoor heat stress hazard and the daytime grid population.

The actual conditions of mesoscale summer high temperatures (HTs) recorded in the Osaka–Kyoto urban area of Japan were investigated using an observation network. The daytime temperatures observed on 10 HT events in this area were the highest in the southern area of Kyoto [area with no Automated Meteorological Data Acquisition System (AMeDAS) observation sites]. To quantitatively evaluate the formation mechanisms of HT events, a heat budget analysis on an atmospheric column was conducted using the Weather Research and Forecasting (WRF) model. The results showed that over the HT area the daytime column temperature increased as a result of sensible-heat diffusion generated from the urban surface at the contribution rate of 54% and as a result of the sensible-heat advection and diffusion supplied from the sides and at the top of the column at the rate of 46% of all sensible heat supplied. To clarify previously unreported effects of synoptic-scale winds under typical summer pressure patterns on the HT events, a sensitivity experiment with no surface heat fluxes, backward trajectory analysis, and Euler forward tracer analysis was performed. These analyses yielded the following findings: 1) sensible heat at the synoptic scale and/or mesoscale was transported from the tropics by circulation patterns along the edge of the Pacific high as well as from tropical cyclones that were present in the vicinity of Japan and 2) airflow over the Kii Mountains also contributes to the HT events.

We estimated wet-bulb globe temperature (WBGT) using measured meteorological data to understand the bioclimates of human living spaces during the summer season. Our research focused on commercial and residential areas of Okayama City, Japan (population ∼700,000). The commercial spaces (CO) mainly consisted of multi-story office buildings, whereas the residential spaces (RE) consisted of one- or two-story residential buildings. On a fine day with southeast winds, the spatially averaged WBGT measured in the CO was higher than that in the RE. The difference was statistically significant and would have caused noticeable discomfort and a high risk of heat disorder for occupants of the CO over the long term. For instance, at 1900 Japan Standard Time (JST), the maximum difference in the WBGT between the CO and RE sites was 2.0°C (23.5°C for the CO and 21.5°C for the RE). From 1800 to 1900 JST, the wet-bulb temperature in the CO was still 1.5–2.0°C higher than that in the RE, even though both areas had the same dry-bulb temperature. This indicates that the CO retained greater amounts of water vapor for longer periods compared to the RE. The wet-bulb temperature in the CO increased rapidly at most observation points when the southeast sea breeze arrived. In contrast, in the RE, the wet-bulb temperature decreased until evening. This difference was caused by moist air transported from a river about 1 km upwind from the CO. The moist air forced an increase in the WBGT and elevated the risk of heat disorder in the CO. The spatially averaged globe temperature of the CO at 1500 JST was 6.2°C lower than that at the RE, causing the WBGT of the CO to decrease. The results suggest that the higher WBGT in the CO was caused by higher wet-bulb temperatures. On a day with southwest winds, the CO and RE showed no difference in WBGT because the river was not included in the upwind source area.

The “Hirodo-kaze,” a local strong wind accompanying the downslope winds in Japan, is examined using a mesoscale numerical model. The model successfully reproduces the major features of the observed Hirodo-kaze that occurred in association with Typhoon Pabuk. During the Hirodo-kaze, the severe downslope winds in the transitional flow develop in the lower troposphere below the mean-state critical layer. The Hirodo-kaze is closely linked to the strong wind region accompanying the severe downslope winds. After the cessation of the Hirodo-kaze, distinct mountain waves dominate in the lower troposphere where the Scorer parameter l2 decreases with height. The region of strong wind retreats windward as the Hirodo-kaze ceases. Temporal changes in the characteristics of mountain waves in the lee of Mt. Nagi are primarily attributed to the changes in the large-scale environmental winds due to the movement of the intense cyclone. Environmental conditions favorable for the occurrence of the Hirodo-kaze include strong northerlies in the lower troposphere overlain by southerlies in the middle troposphere. The intense cyclone that moves over the sea southwest of the Kii peninsula creates favorable environmental conditions that support the occurrence of the Hirodo-kaze.

A coupled model consisting of a multilayer urban canopy model and a building energy analysis model has been developed to investigate the diurnal variations of outdoor air temperature in the office areas of Tokyo, Japan. Observations and numerical experiments have been performed for the two office areas in Tokyo. The main results obtained in this study are as follows. The coupled model has accurately simulated the air temperature for a weekday case in which released waste heat has been calculated from the energy consumption and cooling load in the buildings. The model has also simulated the air temperature for a holiday case. However, the waste heat from the buildings has little influence on the outdoor temperatures and can be neglected because of the low working activity in the buildings. The waste heat from the air conditioners has caused a temperature rise of 1°–2°C or more on weekdays in the Tokyo office areas. This heating promotes the heat-island phenomenon in Tokyo on weekdays. Thus, it is shown that the energy consumption process (mainly with air conditioning) in buildings should be included in the modeling of summertime air temperature on weekdays in urban areas.

A multilayer one-dimensional canopy model was developed to analyze the relationship between urban warming and the increase in energy consumption in a big city. The canopy model, which consists of one-dimensional diffusion equations with a drag force, has three major parameters: building width, distance between buildings, and vertical floor density distribution, which is the distribution of a ratio of the number of the buildings that are taller than some level to all the buildings in the area under consideration. In addition, a simplified radiative process in the canopy is introduced. Both the drag force of the buildings and the radiative process depend on the floor density distribution. The thermal characteristics of an urban canopy including the effects of anthropogenic heat are very complicated. Therefore, the focus of this research is mainly on the basic performance of an urban canopy without anthropogenic heat. First, the basic thermal characteristics of the urban canopy alone were investigated. The canopy model was then connected with a three-dimensional mesoscale meteorological model, and on-line calculations were performed for 10 and 11 August, 2002 in Tokyo, Japan. The temperature near the ground surface at the bottom of the canopy was considerably improved by the calculation with the canopy model. However, a small difference remained between the calculation and the observation for minimum temperature. Deceleration of the wind was well reproduced for the velocity at the top of the building by the calculation with the canopy model, in which the floor density distribution was considered.

東京都心部を対象とし, 都市キャノピー・ビルエネルギー連成モデルを用いて緑化や高アルベド化などの各種ヒートアイランド緩和・省エネルギー方策の効果を評価した. 都市キャノピー・ビルエネルギー連成モデルとは, 鉛直1次元の局地気象モデルに空調負荷計算モデルを組み込み, 街区内の建物の熱負荷や空調によるエネルギー消費量, 気温変動を計算するモデルである. まず典型街区を対象として夏季の晴天日の計算を行い, 各街区タイプにおける空調負荷の生じ方について分析し, また各対策のヒートアイランド緩和効果と省エネルギー効果を定量化した. 次に東京都心部を中心とした約20km×20kmの範囲での広域評価を行い, 各対策の省エネルギー効果を評価した.

The moisture distribution near the ground surface in and around the Japanese cities of Osaka and Kyoto was investigated. From the analysis of observed data, the atmosphere over the suburban areas between coastal Osaka and inland Kyoto was drier than that over Osaka and Kyoto during the daytime hours. This feature differs from results in previous studies and from expectations based on urban and suburban surface heat budgets. To understand the drying mechanism, numerical experiments were performed, using a simplified geometrical model consisting of a straight coastline, a square urban area on the coast, a square inland urban area, and a plateau mountain surrounding the urban areas. The following main results were obtained. First, suburban drying during the daytime was mainly caused by a valley circulation that developed over the surrounding mountain area. In addition, the two heat island circulations that developed over the two urban areas also caused suburban drying. As a consequence, the coexistence of mountain and urban areas caused more notable suburban drying. Second, the amount of suburban drying was greatest when the urban distance was 40‐50 km, which is roughly equal to the actual distance between the Osaka and Kyoto urban areas. Last, temporal changes in moisture and those of suspended particulate matter, SO 2, and NOx concentrations decreased before the arrival of the sea-breeze front. Thus, it is argued that moisture and pollutants were transported by the two heat island circulations that developed over Osaka and Kyoto and by the valley circulations and then were modified by the sea-breeze circulation.

We investigated air-temperature diurnal variations within urban canopy layer, using a coupled model between the urban meteorology and building energy consumption. The main results obtained are as follows. The coupled model reproduces temperature fields during weekdays when a waste heat exists due to energy consumption and cooling needs in buildings, as well as during weekend. The waste heat causes a temperature rising of 1-2°C during the weekdays at the Tokyo office area. However, the temperature rising strongly depends on weatherconditions (e.g., solar radiation and wind speed); the temperature rising is small when the solar radiation fluxand wind speed increase.

Atmospheric activity concentrations of 212Pb and short-lived 222Rndaughters, together with meteorological elements, have been observed continuously atthree sites at Kamisaibara Village in Japan. In addition, atmospheric activity concentrationof 222Rn, equilibrium-equivalent concentration of 222Rn and conditionsof the lower atmosphere were observed for three intensive observation periods at Akawase,one of the three sites in Kamisaibara Village. The equilibrium-equivalent concentration of222Rn is almost the same as the atmospheric activity concentration of short-lived222Rn daughters.

In the current study, the effects of topography and urbanization on the daytime local-circulations in the area of the Osaka-Kyoto plain were investigated using a mesoscale atmospheric model. The main results obtained from the numerical and observational data analyses are as follows: 1) The stagnation of the inland penetration of the sea-breeze front that occurs in the peripheral portion of the Tokyo urban area does not clearly occur in the peripheral portion of the Osaka urban area. The stagnation is attributed to the heat-island circulation that develops over the peripheral portion of the urban area. Because the northern peripheral portion of the Osaka urban area faces mountains, the valley circulation weakens the heat-island circulation; the about 600-m mountains surrounding the Osaka and Kyoto urban areas are the most suitable to cause the weakening of the heat-island circulation. The valley circulation also induces the surface-air-temperature increase over the plain, through an adiabatic process due to its downward flow; the temperature increase strengthens the horizontal pressure gradient between the sea-breeze circulation and inland areas. 2) The surface air over the suburban region between the Osaka and Kyoto urban areas remains drier than that over the Osaka and Kyoto urban areas, until the arrival of the sea-breeze front, even though urban areas were thought to be drier than suburban areas. This dryness results from the fact that the valley circulation transports drier air downward from the upper levels over the suburban area, and transports the surface-air moisture supplied from the ground surface into mountainous areas. The valley circulation also appears to play an important role in the transport of pollutants from the suburban area into mountainous areas. 3) A chain flow, which flows downward from the upper levels over the Osaka urban area to the lower levels over the Kyoto urban area, forms ahead of the sea-breeze front. This flow can result in the transport of pollutants emitted from the Osaka urban area into the inland Kyoto area prior to the transport of pollutants by the sea-breeze circulation. Additionally, the chain flow intensifies the downward flow of the valley circulation over the suburban region between the Osaka and Kyoto urban areas.

A numerical study was conducted of the effects of two nearby urban areas, one coastal and one inland, on the local circulations and transport of urban pollutants, using a 3D mesoscale incompressible and hydrostatic atmospheric model. The Lagrangian Particle Dispersion Model was applied in the atmospheric model to study the transport of pollutants. The main experimental results are as follows: 1) A “chain flow,” which flows downward from the upper layer over the coastal urban area to the lower layer over the inland urban area, is formed as the sea-breeze front moves inland. 2) If an inland urban area exists, the induced sea-breeze–heat-island circulation system is stronger and is maintained longer in time. This feature becomes clearer as the distance between the two urban areas widens. 3) The chain flow efficiently transports coastal urban pollutants into the lower layer over the suburban area, located between the two urban areas, and also to the farther-inland urban area, prior to the arrival of ...

A weak-wind region, whose horizontal scale is comparable to that of an urban area, is occasionally formed ahead of the sea-breeze front, over a large coastal urban area (Yoshikado and Kondo 1989; Yoshikado 1990; Ohashi and Kida 2001). In this study, the characteristics and the formation mechanism of the weak-wind region were investigated, using a 2D mesoscale atmospheric model. The following results were obtained: The weak-wind region is created by the development of the heat-island circulation over the urban area; the heat-island circulation (i.e., the urbanward pressure-gradient-force) weakens the inlandward ambient wind during the morning hours. At that time, the sea-breeze circulation is inessential in creating this weak-wind region. The weak-wind region cannot be created under the influence of the seaward ambient wind. Subsequently, the weak-wind region is persistently formed ahead of the sea-breeze front, and gradually moves inlandward. A long-term balance between the urbanward pressure-gradient-force, and the turbulent mixing, causes such a phenomenon. Thus, interactions among the sea-breeze circulation, heat-island circulation, and inlandward ambient wind play an important role in the above processes. The spatial scale of the weak-wind region strongly depends on the urban size (width), i.e., the spatial scale of the heat-island circulation developing over the urban area, during the daytime hours.

Concentrations of radon 222Rn andair pollutants, meteorological parametersnear the surface and vertical profiles of meteorological elements were measured atUchio (Okayama City, Okayama Prefecture, Japan) 12 km north from the coast ofthe Inland Sea of Japan. In the nighttime, the 222Rn concentration increased in the case of weak winds, but did not increase as much in the case of moderate or strong winds, as had been expected. In the daytime, the 222Rn concentrationheld at a slightly higher than average level for the period from sunrise to about 1100 JST. It is considered that this phenomenon is due to a period of morning calm, that is, a transition period from land breeze to sea breeze.NO, which is sensitive to traffic volume,brought information concerning advection.Oxidant concentrations,which reflect the availability of sunlight,acted in the reverse manner to 222Rnconcentrations. Thus, a set of 222Rn and air pollutants could provide useful information regarding the local conditions of the atmospheric boundary layer.

An analysis was performed of the observed sea breeze circulation penetrating from Osaka Bay to the inland Kyoto basin. A weak wind region (wind speeds of 2 m s -1 or less) of greater than 1000 m in depth, was found just ahead of the inland moving sea breeze front. The formation of the weak wind region was discussed from the view point of the interaction between the sea breeze and heat island circulations. Similar weak wind regions have also been reported to exist in association with the sea breezes observed over the northern periphery of the Tokyo urban area.

We investigated relationships between the flowering phenology of Prunus yedoensis “Somei-yoshino” (cherry blossom) and the local temperatures in Japan. Our observations were carried out across the Okayama Plain, which included Okayama City (about 700,000 inhabitants), from the winter of 2008 to the spring of 2009. Local air temperature (AT) and the globe temperature (GT) were recorded at the tree height. The flowering dates (FDs) of P. yedoensis were earliest in the central commercial area (located at the center of the plain), followed by the north residential area (further inland), and finally the south residential area (seaward). The recorded FDs were related to the period-averaged daily maximum/minimum AT and GT, and the phenologically effective AT and GT defined in this study. Of these parameters, the phenologically effective GTs correlated most with the FDs. Since the GT is determined by AT, solar and infrared radiations, and wind speed, our previous result suggests that a combination of these three components surrounding the tree is more important for budding and flowering than is AT alone. The supposition is supported by the flowering of P. yedoensis being the latest at the coastal region of the Okayama Plain where the AT were higher than at the inland region, excluding the urban area; it is probably caused by stronger winds there than at the other sites.