An Analysis of the Characteristics and Causes of Extremely High Temperature Days in the Yangtze-Huaihe River Basins in Summer 1960-2011

Based on the highest daily temperature records of boreal summers from 1960 to 2011, this study analyzes interannual variations of the extremely high temperature days (EHTDs) in the Yangtze-Huaihe River basins of East China and their associated anomalous atmospheric circulations and sea surface temperature anomalies (SSTAs). Composite results of the summers in which the occurrence frequencies of EHTDs are higher (lower) than normal show that: (1) There is anomalous quasi-barotropic anticyclonic (cyclonic) circulation over the Yangtze-Huaihe River basins accompanied with anomalous descending (ascending) motion due to middle and upper troposphere thermal wind vorticity advection; (2) the position of the westerly jet has a northward (southward) displacement and a Silk Road Teleconnection-like wave train is found embedded in the upper troposphere; (3) prior summer, the central equatorial Pacific Ocean, South China Sea, Bay of Bengal, and Arabian Sea feature significantly positive (negative) SSTAs, while at the same time the SSTAs of the East China Sea and South Sea of Japan are significantly positive (negative). This study also evaluates the abilities of eight models involved in the Coupled Model Intercomparison Project Phase 5 (CMIP5) in simulating the EHTDs of the Yangtze-Huaihe River basins of East China, and the trend of EHTDs under different future emissions scenarios. The results suggest that the boreal summer EHTDs of the Yangtze-Huaihe River basins could reach about 20 d by the end of the 21st century under the 2.6 W m^-2 representative concentration pathway (RCP2.6), and 40 d and 70 d under RCP4.5 and RCP8.5, respectively.