As the Tibetan Plateau (TP) is an important Asian water resource, future changes in precipitation over the TP are an essential part of climate change assessments for the TP and surrounding regions. Here we investigate the water budget over the TP with a global 20-km grid atmospheric general circulation model. Future simulations are performed using CMIP5 multi–model ensemble mean sea surface temperature changes at the end of the 21st century under the RCP8.5 scenario. In the present climate, an east–west contrast in the water budget is noted: over the eastern TP, both moisture flux convergence and local evaporation contribute to summertime precipitation with comparable magnitude; on the other hand, over the western TP, contribution from local evaporation dominates. Under the future climate, precipitation increases over the TP. Contribution from increasing evaporation dominates that from increasing moisture flux convergence into the TP. A prominent east–west contrast is also found in future surface water budget changes. Over the western TP, surface temperature increases are higher, an increasing rate of precipitation is greater, soil moisture becomes wetter, and runoff increases more than over the eastern TP. This suggests that the east–west contrast in surface climate over the TP could become smaller in the future.
We review the philosophy and achievements of the research activity on assessing the impacts of global warming on meteorological hazards and risks in Japan under Program for Risk Information on Climate Change (SOUSEI). The concept of this research project consists of assessing worst-class meteorological hazards and evaluating probabilistic information on the occurrence of extreme weather phenomena. Worst-scenario analyses for historical extreme typhoons and probabilistic analyses on Baiu, warm-season rainfalls, and strong winds with the use of high-performance climate model outputs are described. Collaboration among the fields in meteorology, hydrology, coastal engineering, and forest science plays a key role in advancing the impact assessment of meteorological hazards and risks. Based on the present research activity, possible future directions are given.
Key factors in future changes in wintertime precipitation extremes over an area of the Pacific Ocean side of Japan (the Tokai region) at the end of the 21st century are identified using ensemble simulations projected by a non-hydrostatic regional climate model (NHRCM), driven at the lateral boundaries by an atmospheric general circulation model forcing under the Representative Concentration Pathway 8.5 scenario. The 99th percentile of projected daily precipitation, a measure of precipitation extremes, noticeably increases over the Tokai region in winter. Differences in meteorological variables related to precipitation between the present and future climates are investigated. It is found that a key factor in changes in precipitation extremes is the increases in specific humidity over a deeper layer (from the lower to middle troposphere). The low-level moist flow associated with an extratropical cyclone is southerly and impinges on coastal mountains in the Tokai region, leading to enhanced convergence and precipitation. This orographically induced precipitation can be enhanced when mid-level specific humidity increases in the future climate, as well as at lower levels.
A windthrow refers to the uprooting and overthrowing of trees by the wind. Typhoons are a major cause of windthrows in Japan and are predicted to intensify under global warming. This study aimed to estimate the impact of climate change on windthrows and evaluate possible adaptation measures for sustainable forest management. We incorporated Typhoon Songda (2004) simulation experiments under current and pseudo-global warming (2075–2099, RCP 8.5 scenario) conditions with windthrow modelling in four natural and four artificial (Abies sachalinensis, Pinaceae) forests of Hokkaido. Unexpectedly, pseudo-global warming conditions decreased windthrow probabilities compared with current conditions for both forest types, presumably because wind speeds of the simulated typhoon weakened in Japan’s high-latitude regions. Our results indicate that reconversion of artificial forests into natural forests largely decreased windthrow probability, providing a potential adaptation measure for improved forest management. To fully understand the range of climate-change effects on windthrow in Japan, future studies should use different climate scenarios and data from other typhoons, geographical regions, and forest types.
Recent studies have argued that extreme precipitation intensities are increased in many regions across the globe due to atmospheric warming. This argument is based on the principle of the Clausius-Clapeyron (CC) relationship, which states that the atmosphere can hold more moisture in warmer air temperatures (~7%°C–1). In this study, we investigate the future changes of extreme precipitation intensities associated with temperature over Japan, by analyzing multimodel ensemble downscaling experiments of three RCMs (NHRCM, NRAMS, WRF) driven by one GCM (MIROC3.2) for two climate periods (1981–2000 and 2081–2100, SRES A1B). We find that extreme precipitation intensities are significantly increased by 5–15 mm d–1 for temperatures above ~21°C in the future, compared to the current climate. The extreme precipitation intensities for lower (higher) temperatures below (above) 8–10°C (19–24°C) exhibit super-CC (negative-CC) scaling. The rate of increase of extreme precipitation intensities is also increased by ~2%°C–1 under the SRES A1B scenario (3.4–4.4%°C–1 during 1981–2000 and 5.5–6.5%°C–1 during 2081–2100). We find that the increase of extreme precipitation intensities is associated with strong vertical velocity and substantial increase of water vapor under the future scenario.