Linear and nonlinear causal relationships between the dry/wet conditions and teleconnection indices in the Yangtze River basin

Global precipitation has undergone significant changes due to climate change, resulting in extreme drought and flood events and remarkable losses of life and property. Therefore, based on precipitation and temperature data for the Yangtze River Basin (YRB), as well as teleconnection indices (i.e., Nino3.4, North Pacific Index [NPI], Southern Oscillation Indices [SOI], and Pacific Decadal Oscillation [PDO]), the causal relationship between the teleconnection indices and the dry/wet changes was analyzed and explored using the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI) from 1961 to 2018. Based on the findings, precipitation significantly increased in the upper and lower reaches of the YRB, with a maximum increase of 8 mm/a, and decreased in the middle reaches, with a maximum decrease of 4 mm/a. Further, the temperature in the entire YRB increased, with a maximum increase of 0.04 degrees C/a. The drought characteristics derived from SPI in the YRB were more uniform in spatial distribution from 1961 to 2018, with small local differences and the largest proportion of mild droughts in different drought classes; however, for those from SPEI in the YRB, local differences in spatial distribution and the largest proportion of moderate droughts in different drought classes were found. Finally, both linear and nonlinear causality between the teleconnection indices and the wet/dry changes in the YRB were significant to some extent, especially for NAO, Nino 3.4, and PDO. These causalities between the wet/dry changes and the teleconnection indices were also more significant for short periods. Related studies are important for assessing the driving forces of dry-wet changes in the YRB.