Abstract:

The Yellow river basin, as an ecological barrier zone in northern China, experiences frequent drought events with significant spatiotemporal differentiation. However, its large−scale evolution pattern and atmospheric oceanic driving mechanisms are not yet clear, which hinders the optimal allocation of regional water resources and drought risk management. This study was based on monthly precipitation and temperature data from 340 meteorological stations in and around the Yellow river basin from 1980 to 2020. The Thornthwaite model was used to calculate the Standardized Precipitation Evapotranspiration Index (SPEI), and linear trend estimation, Mann−Kendall trend/mutation test, continuous wavelet transform and wavelet coherence analysis were combined to reveal the spatiotemporal evolution of drought in the Yellow river basin and its multi−scale coupling mechanism with the Arctic Oscillation (AO), Pacific Decadal Oscillation (PDO), El Niño−Southern Oscillation (ENSO) and East Asian Summer Monsoon (EASM), in order to provide scientific basis for regional basin drought warning and adaptive regulation. The results showed that from 1980 to 2020, the spring SPEI−3 in the Yellow river basin significantly decreased at a rate of 0.021·y⁻¹ (P<0.01), and mild or above drought occurred 30% of the time in spring. In autumn of 1997, the detection of SPEI−3 mutation identified a significant jump point, with a 20% increase of droughts within five years thereafter. There was no significant sustained trend of drought in the Yellow river basin during summer and winter, which manifested as short−term random fluctuations. From 1980 to 2020, the annual scale SPEI−12 in the Yellow river basin showed a slight downward trend of 0.005·y⁻¹ (P=0.06). From 1997 to 2002, there were a total of eight occurrences of mild to moderate drought in the Yellow river basin, accounting for 65% of the total annual drought events. In 1986, it suddenly changed to a sustained drought. Spatially, from 1980 to 2020, the high−frequency drought zone in the Yellow river basin migrated from the middle and lower reaches of the northeast to the southwest, forming a radiation belt of "frequent occurrence in the northeast and weakening in the southwest" covering 35.23% of the middle and lower reaches. The Arctic Oscillation (AO) caused a 2−4 month lag in drought in the Yellow river basin through a 3−60 month resonance. The bimodal effect of Pacific Decadal Oscillation (PDO) caused drought to advance or lag by 3−8 months. ENSO multi−cycle alternation caused drought to lag by 3−9 months or advance by 12−18 months. The coupling of short period negative phase and medium to long period positive phase in the East Asian Summer Monsoon (EASM) caused drought to lag by 1−15 months. In summary, the periodic fluctuations of multi−scale weather and climate events were the key driving mechanism for the meteorological drought evolution in the Yellow river basin from 1980 to 2020 through the cross scale synergistic effects of AO suppressing soil moisture, PDO weakening water vapor transport and EASM driving changes. This study can provide reference for regional drought warning and adaptive regulation.

Key words: Yellow river basin, SPEI, Meteorological drought, Wavelet transform, Arctic Oscillation, Pacific Decadal Oscillation