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Trend analysis of extreme precipitation events across Iran using percentile indices
International Journal of Climatology ( IF 3.5 ) Pub Date : 2020-06-15 , DOI: 10.1002/joc.6708 Mehdi Mahbod 1 , Mohammad Rafie Rafiee 1
International Journal of Climatology ( IF 3.5 ) Pub Date : 2020-06-15 , DOI: 10.1002/joc.6708 Mehdi Mahbod 1 , Mohammad Rafie Rafiee 1
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Although a number of studies have been conducted on extreme precipitation trends in different parts of the world including Iran, a great number of such studies have reported only the total amount of daily precipitation greater than a certain percentage (e.g., 95%) of the long term data (R95p), ignoring other useful indices. To address this research gap, we used other modified indices, namely R95tot (fractional contribution of very wet days to annual total amounts), R95tt (fractional contribution of very wet days to the total annual obtained from fitted gamma probability distribution), and RS95 (same as R95tt except that it uses Weibull distribution and very wet days defined by 95 percentage of an individual year) by which the spatial and temporal changes of very wet days across Iran was assessed, 1985–2013. In addition, to evaluate the effect of the selected distribution on the results, a new index‐(RS95gm)—was introduced and reported. This index is similar to RS95, except that it uses gamma distribution instead of Weibull. According to trend analysis of R95p, R95tot, and R95tt, reduced frequency of extreme precipitation events was detected in some northwest, west and northeast parts of Iran. On the contrary, RS95 (RS95gm) results showed a higher frequency of extreme events across Iran. It was also demonstrated that while R95p, R95tot, and R95tt were unequivocally affected by changes in the mean wet‐day/ annual total precipitation, RS95 (RS95gm) was more influenced by changes in the distributional shape, showing more stable trends. Although RS95 and RS95gm were highly correlated with only 19% difference on average, their trend analysis results were not completely consistent (70% agreement). Thus, it may be concluded that any changes in statistical distribution in the calculation of the RS95 would have a considerable effect on whether the obtained trend is significant or not.
中文翻译：
使用百分比指数对伊朗极端降水事件进行趋势分析
尽管已经对包括伊朗在内的世界不同地区的极端降水趋势进行了许多研究，但是大量此类研究仅报告了每天降水总量大于长期降水的一定百分比（例如95％）。期限数据（R95p），而忽略其他有用的索引。为了弥补这一研究空白，我们使用了其他修正指标，即R95 tot（非常湿天的分数对年度总量的贡献），R95 tt（非常湿天的分数对年度总和的拟合贡献，通过伽玛概率分布获得），以及RS95（与R95 tt相同除了它使用威布尔分布和非常潮湿的日子（由每年的95％定义）来评估1985-2013年整个伊朗的非常潮湿的日子的时空变化。另外，为了评估所选分布对结果的影响，引入并报告了新的索引（RS95 gm）。该索引类似于RS95，不同之处在于它使用伽马分布而不是Weibull。根据R95p，R95 tot和R95 tt的趋势分析，在伊朗西北部，西部和东北部发现极端降水事件的频率降低。相反，RS95（RS95 gm）结果显示伊朗各地发生极端事件的频率更高。还证明了R95p，R95tot和R95 tt无疑受到平均湿日/年总降水量变化的影响，RS95（RS95 gm）受分布形状变化的影响更大，显示出更加稳定的趋势。尽管RS95和RS95 gm高度相关，平均差异仅为19％，但它们的趋势分析结果并不完全一致（70％一致）。因此，可以得出结论，RS95计算中统计分布的任何变化都会对所得趋势是否显着产生重大影响。
更新日期：2020-06-15
中文翻译：
使用百分比指数对伊朗极端降水事件进行趋势分析
尽管已经对包括伊朗在内的世界不同地区的极端降水趋势进行了许多研究，但是大量此类研究仅报告了每天降水总量大于长期降水的一定百分比（例如95％）。期限数据（R95p），而忽略其他有用的索引。为了弥补这一研究空白，我们使用了其他修正指标，即R95 tot（非常湿天的分数对年度总量的贡献），R95 tt（非常湿天的分数对年度总和的拟合贡献，通过伽玛概率分布获得），以及RS95（与R95 tt相同除了它使用威布尔分布和非常潮湿的日子（由每年的95％定义）来评估1985-2013年整个伊朗的非常潮湿的日子的时空变化。另外，为了评估所选分布对结果的影响，引入并报告了新的索引（RS95 gm）。该索引类似于RS95，不同之处在于它使用伽马分布而不是Weibull。根据R95p，R95 tot和R95 tt的趋势分析，在伊朗西北部，西部和东北部发现极端降水事件的频率降低。相反，RS95（RS95 gm）结果显示伊朗各地发生极端事件的频率更高。还证明了R95p，R95tot和R95 tt无疑受到平均湿日/年总降水量变化的影响，RS95（RS95 gm）受分布形状变化的影响更大，显示出更加稳定的趋势。尽管RS95和RS95 gm高度相关，平均差异仅为19％，但它们的趋势分析结果并不完全一致（70％一致）。因此，可以得出结论，RS95计算中统计分布的任何变化都会对所得趋势是否显着产生重大影响。
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