Interannual and Interdecadal Climate Variations of Floods in the Western United States

9973125最后，这项拟议的研究试图将低频气候变化与洪水发生频率的非平稳性联系起来。主要关注的是美国西部地区，那里的极端洪水状况主要是冬季/早春融雪和降雨。与行星急流耦合的纬向大气流动机制，而不是对流雷暴，决定了这种事件。该地区洪水的非平稳性已被认识到。自1945年以来，美洲河已经经历了7次洪水，比之前40年估计的100年洪水还要大。因此，加利福尼亚州萨克拉门托的防洪能力可能会大大低于100年。今年洪水来得较早，有迹象表明气温、降水量和雪线的季节性发生了相应的变化。将制定一个分级的贝叶斯框架，将现场和区域洪水过程与结构化的低频气候变率联系起来。将利用历史水文气候数据和海洋-大气环流耦合模式的集合模拟，制定和检验洪水潜力与盆地降水和温度季节性、与大气环流模式、进而与海洋-大气系统的模式和人为气候变化有关的假设。

9973125LallThe proposed research seeks to empirically connect low frequency climate variability to nonstationarity in the frequency of flood occurrence. The primary focus is on regions in the Western United States where the extreme flood regime is dominated by winter/early spring snowmelt and rainfall. Zonal atmospheric flow mechanisms coupled to the planetary jet stream, rather than convective thunderstorms determine such events. Nonstationarity of floods in this region has been recognized. The American River has experienced 7 floods since 1945 larger than the 100 year flood estimated on the basis of the previous 40 years. Sacramento, California may thus have significantly less than 100 year flood protection. The floods have come earlier in the year, and there are indications of corresponding changes in the seasonality of temperature, precipitation and the snow line. A hierarchical, Bayesian framework for relating at site and regional flood processes to structured low frequency climate variability will be developed. Hypotheses that relate flood potential to basin precipitation and temperature seasonality, to atmospheric circulation patterns, and in turn to modes of the ocean-atmosphere system and to anthropogenic climate change will be developed and tested using historical hydroclimatic data and ensemble simulations from a coupled ocean-atmosphere General Circulation Model.