Spatiotemporal changes in precipitation extremes over Yangtze River basin, China, considering the rainfall shift in the late 1970s
Introduction
An increasing interest has been drawn from public, government and academic communities to extreme climate events in recent decades owing to their changes being particularly related to disastrous environmental and socio-economic consequences. The Special Report on Extreme Events (SREX) of the Intergovernmental Panel on Climate Change (IPCC, 2012) also specially emphasized potentially severe impacts from extreme weather and climate phenomenon (e.g., Karl and Easterling, 1999, Beniston, 2004, Alexander et al., 2006), particularly for extreme precipitation, which not only poses adverse effects on agriculture and food security but also results in inundating streets in urban regions (Mishra and Singh, 2010). As the most important topic in climatic community in the last few years, global climate change associated with rising concentrations of anthropogenic greenhouse gases and aerosols in the atmosphere is likely to enhance magnitude and frequency of precipitation extremes in time and space (Meehl et al., 2000, Groisman et al., 2005, Solomon et al., 2007). Moreover, the observational studies, theoretical arguments and model simulation results confirm simultaneously that increasing atmospheric temperature results in higher evaporation rates and enables the atmosphere maintain more water vapor. Meanwhile the convergence of moisture-laden air masses leads to air uplift and cloud formation, which might form eventual intense precipitation (e.g., Menzel and Bürger, 2002, Allan, 2011, Min et al., 2011). Furthermore, numerous previous studies suggested that climate change derived from global warming could lead to increase and intensification of precipitation extremes (Willems et al., 2012, Arnbjerg-Nielsen et al., 2013).
Therefore, better understanding precipitation extremes in the context of climate change is overwhelmingly important and vital to develop meaningful information for hydrological processes (e.g., Gao et al., 2006, Giorgi and Lionello, 2008, Allan and Soden, 2008). Lots of analyses in precipitation extremes have been conducted at regional and local scales around the world. Karl and Knight (1998) suggested that increasing annual total precipitation was strongly influenced by increases of both intensity and frequency of precipitation extremes in United States. Groisman et al. (1999) reported that the probability of daily rainfall exceeding 50.8 mm increased by approximately 20% over mid-latitude countries in later 20th century. This phenomenon was also confirmed by subsequent studies conducted by Frich et al. (2002) and Alexander et al. (2006), who further indicated that the intense precipitation would increase even in the areas where mean rainfall decreased through analyzing large-scale observations. Klein Tank and Können (2003) suggested that most of indices for extreme precipitation events exhibited increasing trends over Europe during the period 1946–1999 at continental scale. Other studies also found more occurrence of extreme precipitation across different geographic regions and timescales (e.g., Solomon et al., 2007, Rahimzadeh et al., 2009, Booth et al., 2012, Fan et al., 2012, Willems et al., 2012, Arnbjerg-Nielsen et al., 2013).
In China, Zhai et al. (1999) analyzed the varying characteristics in precipitation by utilizing different categories of rainfall intensity, for example 10, 50 and 100 mm/day, and reported that the trends of total precipitation were not significant but the frequency of precipitation decreased and the rainfall intensity increased. Liu et al. (2005) suggested that the frequency and intensity of extreme precipitation events contributed mostly to the variations in total precipitation over many regions in China. The positive trends of precipitation extremes appeared in the southeast coastal regions, northwest China and Yangtze River basin (YRB), while the decreasing trends were found in north of northeast China, northern China and Yellow River basin (e.g., Zhai et al., 2005, Qian and Qin, 2008, Zhang et al., 2008). In general, summer precipitation in eastern China exhibits a southern flood and northern drought pattern due to effects of East Asian summer monsoon (EASM). Additionally, coupled with complexly geographical regions, spatial distribution in precipitation extremes exhibits more regional characteristics in China (e.g., Zhai et al., 2005, Dong et al., 2011, Cuo et al., 2014, Zhang et al., 2015). From this perspective, the YRB, becoming the key region for investigating extreme precipitation in China, experienced many flood and drought disasters during recent decades. Accordingly, various studies focusing on above-normal rainfall across YRB were carried out.
As mentioned above, precipitation extremes in mid-lower reaches of YRB is generally characterized by statistically significant positive trends. However, trends in upper basin have not been drawn consistent conclusions among different studies (e.g., Zhai et al., 2005, Zhang et al., 2008, Dong et al., 2011). Su et al. (2006) reported that the maximum precipitation magnitudes for 1, 3 and 7 day were not characterized by any significant trends although the trends increased slightly at basin scale. And the increasing rainstorm (> 50 mm/day) frequency contributed major rainfall to upward trend in summer precipitation in mid-lower reaches of YRB. Meanwhile, the maximum drought spell displayed significant decreasing trend in upper basin. To detect the detailed features in time and space, Zhang et al. (2008) analyzed the variations in annual extreme precipitation and frequency of days with rain/no-rain, and concluded that the significant increasing trends in rainfall intensity were mainly located over southeast, southwest YRB and Yangtze River Delta. The increasing/decreasing trends in rain/no-rain were observed in mid-lower reaches of YRB. However, no obviously coherent trends in annual extreme precipitation were investigated over the whole basin. Su et al. (2008) further investigated spatiotemporal features in precipitation extremes over YRB by utilizing methods of rotated empirical orthogonal function (REOF) and demonstrated that variations in extreme precipitation showed distinctively regional characteristics, no consistent patterns were detected in YRB. Further confirmation is also obtained by Guo et al. (2013), who reported that no general significant increasing/decreasing trend of extreme precipitation indices are found over YRB by analyzing historical recorded rainfall dataset.
Other relevant researches were also conducted to investigate heavy precipitation regime across YRB and adjacent regions (e.g., Becker et al., 2008, Li et al., 2012, Chen et al., 2014). Furthermore, it is noteworthy that summer precipitation, affecting significantly to annual total rainfall in YRB, has experienced distinctly abrupt shift or jump in later 1970s (e.g., Ding et al., 2008). This is also confirmed by studies from observation and simulation (e.g., Bueh, 2003, Gong and Ho, 2002, Gao et al., 2016). The precipitation regime shift in later 1970s inevitably influences the oscillation of above-normal precipitation events over YRB. Qian et al. (2003) and Bueh et al. (2003) indicated that land-sea thermal contrast derived from global climate change influenced the patterns of EASM, accordingly, the seasonal alternation of air mass movement between ocean and continent are changed, which is crucial to the variability of precipitation distribution, and the anomalies presented obviously since 1980 over YRB. Thus, the rainfall shift in later 1970s should be considered when the trends in precipitation extremes are investigated across YRB, otherwise, the natural features of extreme precipitation within long time series would be ignored or blanketed. However, this shift was almost rarely taken into account in the previous studies focusing on trends of precipitation extremes over YRB, which might be the reason why no generally spatial consensus in patterns of precipitation extremes have been obtained. Therefore, the spatiotemporal characteristics in extreme precipitation over YRB need to be re-examined comprehensively by considering the rainfall shift in later 1970s to contribute useful information for prediction of precipitation extremes and long-term risk flood management, this is also the motivation for us to conduct this research. In this study, we select 1980 as the shifty point, accordingly, the period 1960–1980 and 1981–2011 are considered as preclimatic (preceding climatic) and aftclimatic (after climatic) period, respectively.
The objective of this article is to provide a better understanding of the variations and variability of magnitude, frequency and duration of precipitation extremes in different regions across YRB, and to identify whether the precipitation in YRB is becoming more extreme during aftclimatic period. In this study, the detailed analyses of variations in precipitation extremes over YRB are investigated during prec- and aftclimatic periods, respectively, and the comprehensive analyses for the two subperiods are also carried out following the methodology proposed by Mishra and Singh (2010). The rest of the paper is organized as follows: data and methodology as well as study area are introduced in Section 2. The changing features in extreme precipitation events before and after shifty point of rainfall regime in 1980 as well as entire time period are presented in Section 3, followed by conclusions in Section 4.
Section snippets
Study area
The YRB (Fig. 1) is situated in the subtropics with latitude between 24°30′ and 35°45′N and longitude between 90°33′ and 112°25′E. It is the longest river in China and the third longest river over the world in terms of annual mean runoff, only exceeded by the Amazon and Congo Rivers, hence, it plays a significant role in the sustainable economic and social development in China. The river originates in the Tanggula Mountains in the Qinghai-Tibet Plateau in west-central China with some areas
Precipitation characteristics over YRB
As small variations in mean rainfall would play a significant role to the variability of extreme precipitation in selected regions (Groisman et al., 1999), it is necessary to detect the general behaviors of rainfall regime before analyzing variations in precipitation extremes over YRB. Six stations, evenly distributed across YRB, are selected to provide the available understanding of preliminary characteristics in precipitation patterns (Fig. 1). Station 58608 situates in the south of lower
Conclusions
The comprehensively spatial and temporal variations in precipitation extremes during period 1960–2011 are analyzed by fitting a GEV distribution, on the basis of five annual extreme precipitation events: 1, 7 and 30 day annual maximum precipitation, as well as 95th and 97.5th percentiles. The spatiotemporal distribution of precipitation extremes in terms of different magnitudes presents distinct patterns over YRB, even though the annual rainfall amount decreases gradually from southeast coast to
Acknowledgements
We are heartily grateful to editor, Prof. Kendal McGuffie for his generous encouragement and great kindness for kindly providing us an opportunity to improve the quality of this manuscript. And we cordially thank anonymous reviewers for their professional comments and suggestions which are greatly helpful for further improvement of the quality of this manuscript. This study is jointly supported by Natural Science Foundation and Sci-tech Development Project of Shandong Province (No. ZR2015DQ004;
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