Probable causes of the abnormal variations in summer precipitation extremes in the Guangdong-Hong Kong-Macao Greater Bay Area in China.

The Guangdong-Hong Kong-Macao Greater Bay Area (GBA) is one of the most significant increasing areas for summer precipitation extremes in China. In this paper, the number of very heavy precipitation days (R20day) is selected as a representative variable to explore the probable causes of abnormal changes in summer precipitation extremes in recent decades by using the gridded 0.25° × 0.25° observation dataset of CN05.1, NCEP/NCAR Reanalysis 1 with a horizontal resolution of 2.5° × 2.5° and NOAA Extended Reconstructed Sea Surface Temperature (ERSST) V5 with a horizontal resolution of 2.0° × 2.0°. The onset of the South China Sea summer monsoon was early (late), and the R20day in summer was more (less) on both interannual and interdecadal scales. In recent decades, the East Asian summer monsoon and the western North Pacific monsoon weakened, and the R20day in the GBA increased. When the Eurasian teleconnection pattern is in the positive (negative) phase, positive (negative) height anomalies occur in Mongolia and North Central China, and negative (positive) height anomalies occur in South China, which enhances (weakens) vertical upward movements and the south wind anomaly in the lower troposphere in South China, resulting in strong (weak) humidity and more (less) R20day in the GBA. The influences of the Silk Road teleconnection pattern, East Asia/Pacific teleconnection pattern, North Pacific decadal oscillation and western Pacific warm pool strength on R20day are only significant on an interdecadal scale. The North Pacific gyre oscillation has significant effects on the interdecadal change and weakly significant effects on the interannual variation of R20day in the GBA. On an interannual scale, the south-north oscillation of sea surface temperature in the North Pacific and Indian Ocean dipole plays a significant role. [ABSTRACT FROM AUTHOR]