The Tokai region in central Japan often receives heavy rainfall because of typhoons. Furthermore, because of global warming, the intensity of heavy rainfall events is expected to increase in the ...future. Therefore, assessment of possible differences in such events between the present and future is important. In this study, a record heavy rainfall event in the Tokai region on 11 September 2000, the so-called Tokai Heavy Rain (THR), was numerically simulated by weather research and forecasting model with triple nesting grid system of 50-, 10-, and 2-km horizontal resolution. Simulated results present characteristics of rainfall and atmospheric conditions similar to the actual event. Thus, the simulation is considered valid for reproducing rainfall processes of the THR. In addition, variations of heavy rainfall events in future climate scenarios are investigated using numerical simulations based on pseudo global warming (PGW) conditions, constructed using third-phase results of Coupled Model Intercomparison Project multi-model global warming experiments. Under certain future climate scenarios, the Tokai region may experience heavy rainfall events in which maximum hourly rainfall and extent of heavy rainfall areas increases. Such variations are mainly attributed to increased specific humidity in the lower troposphere. In some PGW runs, there was no significant rainfall around the Tokai region. There was increased specific humidity in these runs, and the horizontal distribution of lower atmospheric air temperature was favorable for the formation of a mesoscale convergence zone, as seen in PGW runs with heavy rainfall. However, vertical profiles of equivalent potential temperature and saturated equivalent potential temperature showed unsaturated and stable atmospheric stratifications that are unfavorable for convective activity. Even in cases with increased atmospheric temperature and specific humidity caused by global warming, differences in their spatial distributions and vertical profiles could lead to contrasting effects of global warming on a specific extreme weather event.
The Maunder Minimum (A.D. 1645–1715) is a useful period to investigate possible sun—climate linkages as sunspots became exceedingly rare and the characteristics of solar cycles were different from ...those of today. Here, we report annual variations in the oxygen isotopic composition (δ¹⁸O) of tree-ring cellulose in central Japan during the Maunder Minimum. We were able to explore possible sun—climate connections through high-temporal resolution solar activity (radiocarbon contents; Δ¹⁴C) and climate (δ¹⁸O) isotope records derived from annual tree rings. The tree-ring δ¹⁸O record in Japan shows distinct negative δ¹⁸O spikes (wetter rainy seasons) coinciding with rapid cooling in Greenland and with decreases in Northern Hemisphere mean temperature at around minima of decadal solar cycles. We have determined that the climate signals in all three records strongly correlate with changes in the polarity of solar dipole magnetic field, suggesting a causal link to galactic cosmic rays (GCRs). These findings are further supported by a comparison between the interannual patterns of tree-ring δ¹⁸O record and the GCR flux reconstructed by an ice-core ¹⁰Be record. Therefore, the variation of GCR flux associated with the multidecadal cycles of solar magnetic field seem to be causally related to the significant and widespread climate changes at least during the Maunder Minimum.
A flood frequency analysis using historical flood information was carried out for Lake Biwa since 18th century. The probability distributions of the standardized annual maximum water level andthe ...annual maximum rainfall totals for 30days was investigated and the effects of using historical flood information on flood frequency analysis were examined by plotting position. As results, it became apparent that these two extreme hydrological values obey the Gumbel distribution for Lake Biwa, and it was shown that the estimation precision of the quantile corresponding to the return period of several decades to a hundred years is largely improved by utilizing historical flood information.
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