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

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.

Possible Linkages of Hydrological Variables to Ocean–Atmosphere Signals and Sunspot Activity in the Upstream Yangtze River Basin

“…Due to its proximity to the Pacific Ocean, the Yangtze River basin is prominently sensitive to such climatic phenomena as El Niño-Southern Oscillation (ENSO) [32][33][34][35][36] and Pacific Decade Oscillation (PDO) [33,35,37,38], which have significant implications for forecasting water resources and climate conditions. In recent years, studies in the Yangtze River basin and its tributaries have made significant advances in the influence of large-scale teleconnection patterns on hydrological variability [33,35,37,[39][40][41][42][43][44][45], while the temporal persistence of these relationships is not yet wholly understood. Additionally, as global climate conditions have changed, the intensity and frequency of ENSO events have increased since the late 1970s [26], and ocean-atmosphere forcing has become one of the most potential sources of global natural variability [1]; however, the influence of large-scale climate variability on precipitation and streamflow in the UYRB has rarely been examined.…”