Evaluation of Flood Prediction Uncertainties and its Application to Ungauged Basins

为获得设计洪水，首先确定降雨随预定重现期大小的时空分布模式，然后利用径流模型将降雨分布转换为河流流量。在这里，给定的降雨分布具有不同的模式，径流模型具有局限性。因此，估计的河流排水量包括来自各种来源的不确定因素。洪水预报中的不确定性主要来自1)输入不确定性(时空雨量观测不足)、2)模型结构不确定性(对水文过程的认识不足)、3)参数不确定性(模型参数辨识不足)。这些不确定性主要源于水文观测不足。要解决这一问题，加强观测系统是必要的，但由于预报的对象是百年一遇的洪水，所以加强观测系统是不现实的。因此，有必要研究一种充分利用已测流域信息的无资料流域水文预报方法。1)建立了基于降雨极值尺度特征的降雨强度-历时-频率关系；2)发展了反映降雨极值特征的降雨时间序列生成方法；3)发展了一种根据预测不确定性来评估降雨-径流模型性能的方法。

To obtain design flood, at first some patterns of spatiotemporal rainfall distributions with the magnitude of pre-determined return period is determined, then the rainfall distributions are converted to river discharges using a runoff model. Here, the given rainfall distributions have various patterns and the runoff model has limitations. Thus, the estimated river discharges include uncertainties which come from various sources. Therefore, it is important to evaluate the predictive uncertainty and clarify the sources of the uncertainty to determine design flood.The predictive uncertainty in flood prediction mainly comes from 1) input uncertainty (insufficiency of time and space rainfall observation), 2) model structure uncertainty (insufficiency of the understandings of hydrologic processes), and 3) parameter uncertainty (insufficiency of model parameter identification). These uncertainties essentially stem from insufficient hydrologic observations. To solve the problem, to enhance the observation system is essential, but not practical because the target of prediction is flood which happens e.g. once a hundred years. Therefore, it is requested to develop a hydrologic prediction method for ungauged basins which fully utilize the information at gauged catchments. In this research, followings are conducted to obtain design flood at ungauged basins :1) Development of a intensity-duration-frequency relationships based on scaling characteristics of rainfall extremes2) Development of a rainfall time series generation method which reflects characteristics of rainfall extremes3) Development of a method to assess the performance of rainfall-runoff models in terms of predictive uncertainty.