平成27年関東・東北豪雨時のつくば市真瀬における水蒸気同位体比時間変動の決定要因に関する研究  [in Japanese] Determining factor of vapor isotope ratio during Kanto-Tohoku heavy rain 2015 at Mase Tsukuba city  [in Japanese]

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近年,極端現象増加の報告等により,温暖化など気候変動に対する社会的関心はますます高まりを見せている.しかし極端現象の一つである豪雨などの予測は,その現象自体が非常に局所的な空間スケールで発生するものであるため,これを予測することは困難である.一方,水同位体比は水の相変化に感度を持つ物理量であり,局所的な降水過程の詳細を探ることに利点がある.本研究では,平成27年関東・東北豪雨時に茨城県つくば市真瀬で観測された同位体データを用いることで,豪雨時の同位体比変動について解析した.結果として,短期間に異なる海域からの水蒸気が到達したことが明らかになり,IsoGSMによる水蒸気同位体比(δ<sup>18</sup>O)が9月8日から10日にかけて増減するという挙動が,水蒸気の起源の違いによって引き起こされたということがわかった.降水量効果とは降水同位体比と降水量の統計的な見かけ上の関係のことを通常指すが,この時の水蒸気同位体比の短期変動は,降水をもたらした水蒸気塊が観測地に到達するまでにどれくらいの降水をもたらしてきたかというイベントスケールでの降水量効果による寄与が大きいということがわかった.

 In recent years, social interest in climate change such as global warming has been increasing due to the report of an increase in extreme events. However, prediction such as heavy rain, which is one of extreme phenomena, is difficult to predict since the phenomenon itself occurs on a very local spatial scale. On the other hand, the water isotopic ratio is a physical quantity sensitive to phase change of water, which is advantageous for exploring details of the local precipitation process. In this study, we analyzed the isotope ratio fluctuation during heavy rainfall observed in Mase, Tsukuba city, Ibaraki prefecture during the Kanto and Tohoku heavy rains in September 2015. As a result, it became clear that water vapor from different sea areas reached in a short period of time, and the behavior that the water vapor isotopic ratio (δ<sup>18</sup>O) by IsoGSM increases and decreases from September 8 to 10 is due to the difference in the origin of water vapor. The Amount Effect usually refers to the apparent statistical relationship between the precipitation isotopic ratio and the precipitation amount, but the short-term fluctuation of the water vapor isotope ratio is sensitive to the amount of precipitation which was made along the transport pathway of the mass before reaching to the observation site.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research)

    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 73(5), I_275-I_281, 2017

    Japan Society of Civil Engineers

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