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Abstract
Interdecadal climate changes occurring during the latter half of August (LA) in central Japan are described, and the associated changes in rainfall, typhoon tracks, and circulation patterns over East Asia and the western North Pacific (WNP) regions are investigated. Since 1984, rates of sunshine and temperature have increased, while rainfall has decreased significantly during LA in central Japan. In contrast, rainfall over the Southwest Islands, northern part of Taiwan, and in the south of the middle and lower reaches of the Yangtze River in China has increased. Changes in the positions and tracks of typhoons are responsible for these changes. Prior to 1983, many typhoons approached the central-western part of Japan during LA, while after 1984, most typhoons were deflected away from Japan and moved northwestward to Taiwan and China. The North Pacific subtropical high during LA extended more westward after 1984, which affected the interdecadal changes in sunshine, temperature, rainfall, and typhoon tracks, not only in central Japan, but also over East Asia and the WNP regions.
Abstract
Interdecadal climate changes occurring during the latter half of August (LA) in central Japan are described, and the associated changes in rainfall, typhoon tracks, and circulation patterns over East Asia and the western North Pacific (WNP) regions are investigated. Since 1984, rates of sunshine and temperature have increased, while rainfall has decreased significantly during LA in central Japan. In contrast, rainfall over the Southwest Islands, northern part of Taiwan, and in the south of the middle and lower reaches of the Yangtze River in China has increased. Changes in the positions and tracks of typhoons are responsible for these changes. Prior to 1983, many typhoons approached the central-western part of Japan during LA, while after 1984, most typhoons were deflected away from Japan and moved northwestward to Taiwan and China. The North Pacific subtropical high during LA extended more westward after 1984, which affected the interdecadal changes in sunshine, temperature, rainfall, and typhoon tracks, not only in central Japan, but also over East Asia and the WNP regions.
Abstract
In this study, the impact of global climate change and anticipated urbanization over the next 70 years is estimated with regard to the summertime local climate in the Tokyo metropolitan area (TMA), whose population is already near its peak now. First, five climate projections for the 2070s calculated with the aid of general circulation models (GCMs) are used for dynamical downscaling experiments to evaluate the impact of global climate changes using a regional climate model. Second, the sensitivity of future urbanization until the 2070s is examined assuming a simple developing urban scenario for the TMA. These two sensitivity analyses indicate that the increase in the surface air temperature from the 1990s to the 2070s is about 2.0°C as a result of global climate changes under the A1B scenario in the Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios (SRES) and about 0.5°C as a result of urbanization. Considering the current urban heat island intensity (UHII) of 1.0°C, the possible UHII in the future reaches an average of 1.5°C in the TMA. This means that the mitigation of the UHII should be one of the ways to adapt to a local temperature increase caused by changes in the future global climate. In addition, the estimation of temperature increase due to global climate change has an uncertainty of about 2.0°C depending on the GCM projection, suggesting that the local climate should be projected on the basis of multiple GCM projections.
Abstract
In this study, the impact of global climate change and anticipated urbanization over the next 70 years is estimated with regard to the summertime local climate in the Tokyo metropolitan area (TMA), whose population is already near its peak now. First, five climate projections for the 2070s calculated with the aid of general circulation models (GCMs) are used for dynamical downscaling experiments to evaluate the impact of global climate changes using a regional climate model. Second, the sensitivity of future urbanization until the 2070s is examined assuming a simple developing urban scenario for the TMA. These two sensitivity analyses indicate that the increase in the surface air temperature from the 1990s to the 2070s is about 2.0°C as a result of global climate changes under the A1B scenario in the Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios (SRES) and about 0.5°C as a result of urbanization. Considering the current urban heat island intensity (UHII) of 1.0°C, the possible UHII in the future reaches an average of 1.5°C in the TMA. This means that the mitigation of the UHII should be one of the ways to adapt to a local temperature increase caused by changes in the future global climate. In addition, the estimation of temperature increase due to global climate change has an uncertainty of about 2.0°C depending on the GCM projection, suggesting that the local climate should be projected on the basis of multiple GCM projections.
Abstract
The overall performance of general circulation models is often investigated on the basis of the synthesis of a number of scalar performance metrics of individual models that measure the reproducibility of diverse aspects of the climate. Because of physical and dynamic constraints governing the climate, a model’s performance in simulating a certain aspect of the climate is sometimes related closely to that in simulating another aspect, which results in significant intermodel correlation between performance metrics. Numerous metrics and intermodel correlations may cause a problem in understanding the evaluation and synthesizing the metrics. One possible way to alleviate this problem is to group the correlated metrics beforehand. This study attempts to use simple cluster analysis to group 43 performance metrics. Two clustering methods, the K-means and the Ward methods, yield considerably similar clustering results, and several aspects of the results are found to be physically and dynamically reasonable. Furthermore, the intermodel correlation between the cluster averages is considerably lower than that between the metrics. These results suggest that the cluster analysis is helpful in obtaining the appropriate grouping. Applications of the clustering results are also discussed.
Abstract
The overall performance of general circulation models is often investigated on the basis of the synthesis of a number of scalar performance metrics of individual models that measure the reproducibility of diverse aspects of the climate. Because of physical and dynamic constraints governing the climate, a model’s performance in simulating a certain aspect of the climate is sometimes related closely to that in simulating another aspect, which results in significant intermodel correlation between performance metrics. Numerous metrics and intermodel correlations may cause a problem in understanding the evaluation and synthesizing the metrics. One possible way to alleviate this problem is to group the correlated metrics beforehand. This study attempts to use simple cluster analysis to group 43 performance metrics. Two clustering methods, the K-means and the Ward methods, yield considerably similar clustering results, and several aspects of the results are found to be physically and dynamically reasonable. Furthermore, the intermodel correlation between the cluster averages is considerably lower than that between the metrics. These results suggest that the cluster analysis is helpful in obtaining the appropriate grouping. Applications of the clustering results are also discussed.
