Spatiotemporal Changes in Extreme Wet and Dry Conditions and Linkages with Planetary Oscillations

Abstract

Exploration of the spatiotemporal changes in extreme wet and dry events and their linkages with planetary oscillations is highly necessary for regional hazards mitigation. In this study, a standardized Surface Humid Index was applied for characterizing extreme dry and wet conditions (hereafter referred to as EDWC) in the Wei River Basin (WRB), China. Then, the heuristic segmentation method was adopted to determine the stationarity of extreme dry and wet frequency. The cross wavelet transform and coherence were used to reveal the linkages between EDWC and planetary oscillations. Results indicated that: (1) the standardized Surface Humid Index in the WRB has a striking trend towards wetter condition in summer and winter, whilst that in spring and autumn has a marked trend towards drier condition; (2) the northern basin has the highest extreme wet frequency, while the western basin has the lowest extreme dry and wet frequency; (3) the stationarity of the extreme dry and wet frequency series in the WRB is valid; (4) the planetary oscillations strongly affect the EDWC in the WRB. El Niño Southern Oscillation exhibits the strongest impacts on its EDWC, while Atlantic Multidecadal Oscillation shows the weakest impacts on its EDWC.