Analysis of flood and streamflow timing has recently gained prominence as a tool for attribution of climatic changes to flooding. Such studies generally apply circular statistics to the day of maximum flow in a calendar year and use nonparametric linear trend tests to investigate changes in flooding on a local or regional scale. Here we investigate both the center timing of streamflow and the day of maximum flow using a local water year. For each station, the start of the water year is defined as the month of lowest average monthly streamflow. This definition of water year prevents ambiguity in the direction of computed trends and enables flood and streamflow timing to be described by a normal distribution. Using the assumption of normality, we calculate the historical trend in both flood and streamflow timing using linear regression. While shifts in flood and streamflow timing are consistent with climate change and are shifting in a similar direction, shifts in the timing of the annual maxima flood are approximately three times that of streamflow timing. The results here have implications for water resources and environmental management where streamflow and flood timing are critical to planning. The applicability of the normal approximation to flood and streamflow timing will enable future analyses to use parametric statistics.

中文翻译：

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基于当地水年的全球洪水和水流时间变化趋势

洪水和水流时间分析作为一种将气候变化归因于洪水的工具，最近得到了重视。此类研究通常将循环统计应用于日历年的最大流量日，并使用非参数线性趋势检验来调查局部或区域规模的洪水变化。在这里，我们使用本地水年调查流量的中心时间和最大流量的日期。对于每个站，水年的开始定义为平均月流量最低的月份。水位的这种定义可以防止在计算趋势的方向上产生歧义，并可以用正态分布描述洪水和水流的时间。使用正态性假设，我们使用线性回归计算洪水和水流时间的历史趋势。洪水和水流时间的变化与气候变化是一致的，并且在相似的方向上变化，而每年最大洪水的时间变化大约是水流时间的三倍。这里的结果对水资源和环境管理具有影响，因为水流和洪水时间对规划至关重要。洪水和水流时间的正态近似的适用性将使将来的分析能够使用参数统计。