Spatiotemporal characteristics and attribution of dry/wet conditions in the Weihe River Basin within a typical monsoon transition zone of East Asia over the recent 547 years

https://doi.org/10.1016/j.envsoft.2021.105116Get rights and content

Highlights

  • Developed a new framework to attribute dry/wet spatiotemporal variability on multiple time scales.

  • Revealed four unique hydroclimatic subregions for the Weihe River Basin.

  • Identified the effects of monsoons, plateau circulation, westerly, and solar activities on Weihe.

  • Dry/wet conditions of the subregions show opposite responses to solar activity.

Abstract

The Weihe River Basin (WRB) in a monsoon transition zone of East Asia interacts with multiple weather systems and is susceptible to floods and droughts. We developed a framework based on the Empirical Orthogonal Function analysis, Complete Ensemble Empirical Mode Decomposition with Adaptive Noise analysis, and moving-average based Spearman rank correlation to identify the spatial patterns of the dry/wet conditions from 1470 to 2016, decompose the dry/wet index into the leading components with a period between 2 and 3 years and 100+ years, and discover their driving forces on multiple time scales. Results show that WRB can be divided into four distinguishable hydroclimatic subregions located in the southeast, west, central, and north. The East Asian summer monsoon and South Asian summer monsoon impact this region mainly on the inter-annual and inter-decadal scales, while the impacts of ENSO, PDO, AO, and NAO are dominant on the multi-decadal and centennial scales.

Introduction

A monsoon system acts as an important part of the global climate system and anomalous summer monsoon activities can trigger floods and droughts (Hao et al., 2016; Ninomiya, 1999). Every monsoon system has a limited influential area and usually creates two types of hydroclimatic zones, namely, humid and arid regions. The monsoon transition zone, corresponding to the climate transition zone, is a region where cold-dry and warm-wet air masses frequently encounter; as a result, its climate exhibits significant fluctuation with a high amplitude and large spatial variability on multiple time scales. Therefore, flood and drought possibly co-occur in this area, where dry/wet conditions differ considerably in space. These phenomena greatly influence the prevention and control of floods and droughts in this area (Chao et al., 2019, 2020; Huang et al., 2019; Huo et al., 2020; Li et al., 2011; Luo et al., 2018; Mu et al., 2021; Zhang, 2004; Zhang et al., 2021). Moreover, the monsoon transition zone is mainly composed of semi-arid regions, which have fragile ecosystems and are extremely susceptible to floods and droughts (Guan et al., 2019; Zhang et al., 2019a; Zhu et al., 2020). Therefore, exploring the characteristics of dry/wet variation in the monsoon transition zone is quite important.

The dry/wet conditions of a region are complicatedly affected by various factors such as monsoon system, atmospheric oscillation, solar activities, and geographic features (Hong et al., 2010; Tian et al., 2020; Wang et al., 2019b). Solar activities are an external driving factor, while atmospheric oscillation and monsoon system are internal factors influencing the dry/wet conditions (Bhalme and Mooley, 1980; Fang et al., 2019; Higgins et al., 2000; Hurrell et al., 2003; Liu et al., 2017; Mohmmed et al., 2018; Zhang et al., 2007, 2008; Zhao and Han, 2005). Barlow et al. (2001) revealed the significant relationships between the three primary modes of Pacific sea surface temperature variability and the American warm season hydroclimate. Li et al. (2021) found that global warming, El Niño/Southern Oscillation (ENSO), and local effects are all significant driving factors controlling the spatiotemporal variability of precipitation extremes over the Yangtze River Basin. Besides, many studies were carried out to reveal the relationships between regional dry/wet conditions and their driving factors across the world (Han et al., 2019; Shi et al., 2016; Wang et al., 2019c; Zaroug et al., 2014; Zhang et al., 2015; Zhao et al., 2012). However, most of these studies in the monsoon transition zones are focused on the time scales between annual and centennial scales. Very few studies investigated the dry/wet conditions and their driving forces beyond the centennial scale. In addition, the impacts of different driving factors on the dry/wet conditions in monsoon transition zone have substantially spatial differential patterns and intensities on different time scales, which are rarely explored in the literature.

China's precipitation is mainly influenced by monsoons, westerly, and plateau circulation systems, while their impacts are closely related to the northern edge of East Asian summer monsoon zone (Zhang et al., 2019c). The regions to the south of the northern edge of East Asian summer monsoon zone are mainly controlled by the monsoon system, while those to the north are mainly dominated by the westerly system. However, the northern edge of the East Asian summer monsoon zone will oscillate between south and north with the varying intensity of East Asian monsoon every year (Ma et al., 2011). The oscillation zone corresponds to the monsoon transition zone. Due to the oscillation of the edge, the monsoon transition zone is subjected to the coupling effect of East Asian monsoon system and mid-latitude westerly system, which leads to a great spatial variability of dry/wet conditions.

The Weihe River Basin, located in northwestern inland of China, is the largest sub-basin of the Yellow River and located within the East Asian monsoon transition zone (Yang et al., 2019). At present, the boundary of the East Asian monsoon zone is still under a great debate (Shi et al., 2009); thus, no consensus is reached on the climatic zoning classification of the Weihe River Basin. In addition, the dry/wet conditions in the Weihe River Basin have large spatiotemporal variability, making it very hard to be predicted. Based on the previous studies, the factors influencing the dry/wet conditions of the Weihe River Basin include the Asian summer monsoon systems such as East Asian Summer Monsoon (EASM) and South Asian Summer Monsoon (SASM), atmospheric oscillations such as ENSO, Pacific Decadal Oscillation (PDO), Arctic Oscillation (AO), and North Atlantic Oscillation (NAO), and other natural driving factors like solar activities (Bi et al., 2013; Liu et al., 2017; Wan et al., 2018; Zhao et al., 2015). In most of the previous studies, the EASM and SASM systems in the Asian summer monsoon system are not isolated from each other. EASM and SASM together serve as the two main components of the Asian summer monsoon system (Huan and Li, 2018). The two monsoons differ largely in their circulation characters and impacting areas, and are physically separated and closely correlated to each other (Tao, 1987). The spatial patterns and intensities of the impacts of the EASM and SASM systems on the dry/wet conditions in the Weihe River Basin remain to be further explored.

The objectives of this study are: (1) to reveal the spatial patterns of dry/wet conditions in the Weihe River Basin, (2) to reconstruct the dry/wet index series of the Weihe River Basin from 1470 to 2016 and derive its periods, trends, and changes, and (3) to identify the driving factors of the dry/wet conditions and reveal the spatial patterns of their influences on multiple time scales. This study is valuable for better projecting future changes in this region and its surrounding areas.

Section snippets

Study area

Our study area is the Weihe River Basin (Fig. 1). The Weihe River, located in the east of the northwest inland of China, originates from Niaoshu Mountain in Weiyuan County, Gansu Province, and finally merges into the Yellow River at Tongguan County, Shaanxi Province (Fig. 1). It flows through three provinces in China, including Gansu, Ningxia, and Shaanxi. Located within 33.5°–37.5°N in latitude and 103.5°-110.5°E in longitude, this basin has a total area of 134,800 km2 and is characterized by

Subregion division

Since the Weihe River Basin spans an area of 134,800 km2, it is important to investigate the spatial variability of dry/wet conditions and their potentially differential responses to the driving factors. Therefore, it is important to divide the Weihe River Basin into certain subregions based on the spatial patterns and temporal variation of dry/wet conditions. It is generally regarded that extreme precipitation events are the main causes of floods, while persistent low rainfall is the main

Spatial patterns of precipitation characteristics and hydroclimatic division of the Weihe River Basin

Fig. 3 shows the spatial patterns of the two leading EOF modes of the seven precipitation indices. The seven precipitation indices represent different characteristics of precipitation across the Weihe River Basin. RX1day and RX5day quantify the intensities of precipitation extremes, while R10 and R25 measure the frequencies of precipitation events. CWD and CDD denote the duration of precipitation days and non-precipitation days, respectively, while PRCPTOT quantifies annual precipitation amount

Conclusions

In this study, we investigated the dry/wet conditions of the Weihe River Basin, which is an important monsoon transition zone in China and is influenced by the monsoons, westerly, plateau circulation system and regional to global atmospheric oscillations, from 1470 to 2016. We reconstructed the dry/wet conditions based on historical writings and station observations from 1470 to 2016. We further analyzed the variability of dry/wet conditions of this region on multiple time scales from biennial

CRediT authorship contribution statement

Xinyu Chen: Conceptualization, Data curation, Investigation, Methodology, Software, Formal analysis, Visualization, Writing - original draft. Quan Quan: Conceptualization, Investigation, Methodology, Software, Formal analysis, Writing - review & editing, Funding acquisition. Ke Zhang: Conceptualization, Investigation, Software, Methodology, Formal analysis, Writing - original draft, Writing – review & editing, Funding acquisition. Jiahua Wei: Software, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by the National Key Research and Development Program of China (2016YFA0601503, 2017YFC0403600, and 2016YFC0402701), the Belt and Road Special Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering (2019491411), Hydraulic Science and Technology Plan Foundation of Shaanxi Province (2019slkj-B1), Fundamental Research Funds for the Central Universities of China (B200204038), Natural Science Foundation of Jiangsu Province (BK20180022),

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