Uncertainty in hottest years ranking: analysis of Tibetan Plateau surface air temperature

气温剧烈变化可通过诸如热浪等极端天气气候事件对全球农业、水循环和生态系统等造成不利影响。因此,气候变化研究中的一个重要指标是对各种极端冷暖年份进行高低排序。本文采用Wilcoxon符号秩和检验和蒙特卡洛模拟研究了近几十年来青藏高原极端高温年的高低排序及其不确定性。结果显示,青藏高原前十个极端高温年均发生在1998年之后,其中最热的三年为2006、2009和2010年。当考虑抽样误差和观测误差后,仅有五年有概率成为最热年份,其概率最高的三年为2006(47.231%),2009(40.390%)和2010(12.376%)。此外,对于某一年份是否有概率成为最暖的十年,结果表明Wilcoxon符号秩和检验结果中前十个最暖年份均有超过10%的概率,而2001和2002年仅有3%和4%的概率成为最暖的十年。

Changes in surface air temperature can directly affect hydrology, agriculture, and ecosystems through extreme climate events such as heat waves. For this reason, and to improve climate change adaptation strategies, it is important to investigate the ranking of hottest years. In this study, the Wilcoxon signed-ranktest and Monte Carlo simulation are used to estimate the ranking of the hottest years for theTibetan Plateau （TP） in recent decades, and the uncertainty in the ranking.The Wilcoxon signed-rank test shows that the top 10 hottest years on record over the TP mainly occur after 1998. The top three hottest years are ranked as 2006, 2009, and 2010, but there is almost no significant difference between them. When both sampling and observational errors are considered, only five years have a non-zero probability of being the hottest year, with the three highest probabilities being for the years 2006 （-47.231%）, 2009 （-40.390%）, and 2010 （-12.376%）. Similarly, with respect to a given year that is among the 10 hottest years, our results show that all the years among the ranks of 1-10 resulting from the Wilcoxon signed-rank test have probabilities above 10%, while the years 2001 and 2012 have probabilities of 3% and 4%.