Analysis on the Characteristics of Dry and Wet Periods in The Yangtze River Basin

Hao Huang,Yanqiang Cui,Bo Zhang,Shangqian Ma

doi:10.3390/w12112960

Abstract

As China’s main grain producing region, the Yangtze River basin is vulnerable to changes in wet and dry conditions. In this study, the monthly scale of standardized precipitation evapotranspiration index (SPEI) was calculated, based on the Penman–Monteith equation from 239 meteorological stations in the Yangtze River basin, from 1960 to 2017. Water regime characteristic areas of the Yangtze River basin were extracted and divided using the rotating empirical orthogonal function (REOF). The linear trend of the drought and wetness indicators, the abrupt changes of the rotated principal component time series (RPCs), and the change periods of the drought/wetness intensity (DI/WI) in each subregion were analyzed and discussed. Subsequently, the effects of El Niño-southern oscillation (ENSO) and arctic oscillation (AO) on drought and wetness events were discussed. The results showed that the Yangtze River basin has the characteristic of coexistence of drought and wetness, and drought and wetness of similar severity tend to occur in the same region. There were six subregions extracted through REOF, based on the monthly scale of SPEI, of which the northwestern pattern had an aridization tendency. The stations with significantly increased wetness were located in the middle and eastern basin. The stations in the south of the northwestern pattern, and the west of the southern pattern, had a tendency of wetting in the first 29 years, however, there has been a significant tendency of drying in this region in the last 29 years, which was caused by an abrupt change in 1994. In addition, other patterns had multiple abrupt changes, resulting in multiple transitions between dry and wet states. The principal periods of WI in the southern pattern and northern pattern were longer than the DI, but in other subregions DI was longer than WI. ENSO and AO had the most obvious influence on DI and WI. Compared with the cold phase of ENSO, the DI/WI in the warm phase were higher/lower; compared with the negative phase of AO, both DI and WI were higher in the positive phase. The Hurst index showed that the current dry and wet conditions in the Yangtze River basin have persistent characteristics, the dry conditions in each subregion will continue in the future, and there were a few wetness indicators with weak anti-persistence.

Highlights

Climate warming has a profound impact on the global ecological environment
Areas with more than 25 severely dry and wet months are widely distributed in the whole basin (Figure 2(d1,d2)), indicating that the probability of severe drought and wetness events in the whole basin was relatively close
The Yangtze River basin runs through the monsoon region of China, where climate change is affected by large-scale atmospheric ocean circulation, resulting in frequent and alternating droughts and floods

Summary

Introduction

Climate warming has a profound impact on the global ecological environment. In the context of climate change, the pattern of water balance is changing [1,2,3], the surface evapotranspiration is increasing due to climate warming, and the uneven spatial and temporal distribution of interannual precipitation is strengthened, which leads to the increasing intensity and frequency of droughts, floods, and other disasters [4,5]. The response of drought and wetness changes in different regions to global warming is different. In the past 120 years, drought has increased in different parts of the United. In Italy, the climate has transformed to drought, and the precipitation has decreased by 0.47%·a−1 in the last 57 years [8]. In China, the northwest region is relatively arid, and Lian et al (2019) [10]

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Conclusion