面向事件过程的秦岭南北极端降水时空变化特征

基于72个气象站点1970—2017年逐日降水和气温数据,面向极端降水过程,对秦岭南北4种极端降水类型（偏前型、偏后型、均衡型和单日型）时空变化特征进行分析,进而探讨不同分区、不同类型极端降水与区域增温的响应关系。结果表明：① 从长期气候角度分析,秦岭南北降水格局稳定,3个分区降水变化空间响应具有一致性,共同表现出“降水以波动为主,降水量近期增加,降水日数下降,整体呈现极端化”的特征;② 在极端降水主导类型上,以累计降水量为判断标准,秦岭以北为均衡型主导,兼有偏后型;秦岭南坡类型组合关系较弱,为单一均衡型,汉江谷地西侧为“均衡型+偏后型”,东侧为“均衡型+偏前型”组合;以累积降水频次为判断标准,秦岭南北主导类型为偏前型,其次是偏后型,汉江谷地“偏前型+偏后型”组合形态更突出;③ 秦岭南北极端降水与区域变暖关系密切。当气温升高时,持续性极端降水呈下降趋势,单日型极端降水呈增加趋势。其中,秦岭以北偏前型和均衡型极端降水在下降,秦岭南坡响应密切的为偏后型,汉江谷地为均衡型和偏后型;④ 面向极端降水事件过程,将极端降水事件细化,可有效验证极端降水对气候变暖响应的结论,对未来研究方法完善和研究思路设计具有启示性。

Variability of the event-based extreme precipitation in the south and north Qinling Mountains

Modeling extreme precipitation processes could provide a pathway for a better understanding of the questions concerning how much precipitation is extreme and how that extreme precipitation responds to warming in the climate change sensitive and ecological fragile zone of China over the coming decades. In this perspective, based on daily precipitation and temperature data from 72 meteorological stations released by the National Meteorological Information Center, the spatial-temporal variation of precipitation is investigated in the Qinling Mountains from 1970 to 2017, which is a critical geographical and climatic boundary between northern subtropical and warm temperate zone in China. Then we applied a framework to identify the dominant pattern of EEP in the study region, and time distribution pattern (TDP) of the event-based extreme precipitation (EEP) could be divided into four types, i.e. early, after, balance-phase and single day EEP, here after referred to as TDP1, TDP2, TDP3 and 1-day EEP. More specifically, the relationship between different EEP and local temperature is investigated through the cross wavelet transform and linear correlation. The result showed that from a long-term climate view, precipitation pattern is relatively stable in the Qinling Mountains in the past 48 years, and the 800 mm isohyetal line is still distributed in the south piedmont of Qinling Mountains. Moreover, precipitation analysis showed an obvious synchronous trend in the sub-region, which could be characterized as non-smooth and non-linear, and after 1997, there is an increasing trend in annual precipitation amount, a declining trend in rainy days, and a continuous increase of extreme precipitation intensity. Spatially, according to percentage of total precipitation amount of EEP, a wide distribution of TDP3 is clearly seen over most regions and 1-day EEP does not prevail, which demonstrates that daily precipitation extremes during an EEP could be mainly distributed at both the first and second half parts of the event duration. In north of Qinling Mountains, the dominant pattern combines TDP3 and TDP2. For south piedmont of Qinling Mountains, it witnesses fewer combinations of EEP. There exists difference between the east and west in Hanjiang River Valley, that is, TDP3 and TDP2 in the west is greater than in the east where the dominance of TDP1 and TDP3 is more prominent. However, based on the percentage of total frequency of EEP, TDP1 is observed in southern and northern Qinling Mountains, and the dominant pattern combines TDP1 and TDP2 in Hanjiang River Valley. Furthermore, in the past 48 years, the influence of local climate change, for the decadal variation of extreme precipitation, was more obvious on the time scale of 8-12 years than of on the time scale of 4-8 years. It is worth mentioning that changes in nearly all indices had a strong correlation to temperature in Hanjiang River Valley, especially TDP2 and 1-day EEP. This is particularly true of high temperature related to more precipitation intensity of single day, which in turn raises the expectation of more intense extreme short-duration rainfall events that could be assessed by the wavelet coherence analysis. Between 1998 and 2012, the phenomenon, 'global warming hiatus', occurred in the Qinling Mountains, which led to the decrease of 1-day EEP, and the increases of TDP1 and TDP3 in the north of Qinling Mountains, as well as the increase of TDP2 over the south piedmont of Qinling Mountains. All the above results are closely linked to lower temperature. The response of TDP3 and TDP2 is stronger than other types in Hanjiang River Valley. It should be noted that these results are helpful to understand the relationship between climate warming and extreme precipitation, but the response of different EEP to anthropogenic forcing and atmospheric oscillation is still complex and not explicitly resolved.