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Non-stationarity in daily and sub-daily intense rainfall - Part 1: Sydney, Australia

机译：每日和次每日强降雨中的非平稳性-第1部分：澳大利亚悉尼

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This study was driven by a need to clarify how variations in climate might affect intense rainfall and the potential for flooding. Sub-daily durations are of particular interest for urban applications. Worldwide, few such observation-based studies exist, which is mainly due to limitations in data. While there are still large discrepancies between precipitation data sets from observations and models, both show that there is a tendency for moist regions to become wetter and for dry regions to become drier. However, changes in extreme conditions may show the opposite sign to those in average conditions. Where changes in observed intense precipitation have been studied, this has typically been for daily durations or longer. The purpose of this two-part study is to examine daily and sub-daily rainfall extremes for evidence of non-stationarity. Here the problem was addressed by supplementing one long record (Part 1) by a set of shorter records for a 30-yr concurrent period (Part 2). Variations in frequency and magnitude of rainfall extremes across durations from 6 min to 72 h were assessed using data from sites in the south-east of Australia. For the analyses presented in this paper, a peaks-over-threshold approach was chosen since it allows investigating changes in frequency as well as magnitude. Non-parametric approaches were used to assess changes in frequency, magnitude, and quantile estimates as well as the statistical significance of changes for one station (Sydney Observatory Hill) for the period 1921 to 2005. Deviations from the long-term average vary with season, duration, and threshold. The effects of climate variations are most readily detected for the highest thresholds. Deviations from the long-term average tend to be larger for frequencies than for magnitudes, and changes in frequency and magnitude may have opposite signs. Investigations presented in this paper show that variations in frequency and magnitude of events at daily durations are a poor indicator of changes at sub-daily durations. Studies like the one presented here should be undertaken for other regions to allow the identification of regions with significant increase/decrease in intense rainfall, whether there are common features with regards to duration and season exhibiting most significant changes (which in turn could lead to establishing a theoretical framework), and assist in validation of projections of rainfall extremes.
机译：这项研究的动力是需要弄清气候变化如何影响强降雨和洪水泛滥的可能性。对于城市应用，次日持续时间特别受关注。在世界范围内，很少有这种基于观察的研究，这主要是由于数据的限制。尽管来自观测和模型的降水数据集之间仍然存在较大差异，但两者都表明，潮湿地区趋于湿润，而干旱地区趋于干燥。但是，极端条件下的变化可能显示出与普通条件下相反的信号。在研究了观测到的强降水变化的地方，这通常持续了一天或更长时间。 这项由两部分组成的研究的目的是检查每日和每天次降雨的极端情况，以证明不平稳。在这里，通过在30年的并发期间（第2部分）用一组较短的记录补充一个长记录（第1部分）来解决此问题。使用澳大利亚东南部站点的数据评估了6分钟至72小时持续时间内极端降雨的频率和强度变化。对于本文中介绍的分析，选择了“峰值-阈值”方法，因为它可以调查频率和幅度的变化。非参数方法用于评估1921年至2005年期间一个站点（悉尼天文台山）的频率，幅度和分位数估计的变化以及变化的统计显着性。与长期平均值的差异随季节而变化，持续时间和阈值。对于最高阈值，最容易检测到气候变化的影响。频率与长期平均值的偏差往往大于幅度，并且频率和幅度的变化可能具有相反的符号。 本文所进行的调查表明，每天持续时间中事件发生频率和强度的变化不足以指示次每日持续时间中事件的变化。应该针对其他地区进行类似此处介绍的研究，以识别强降雨中显着增加/减少的地区，关于持续时间和季节是否具有显示最大变化的共同特征（反过来可能导致确定一个理论框架），并有助于验证极端降雨的预测。

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