Concurrent occurrence of droughts and floods between the upper Hanjiang River and northern North China at multi-temporal scales: an association with Arctic Oscillation

The Middle Route of the South-to-North Water Diversion (MSNWD) project’s water source area (the Upper Hanjiang River; UH) and receiving area (northern North China; NNC) exhibit co-drought phenomena at multiple time scales. However, the common atmospheric and environmental factors driving the concurrent occurrence of the climate disasters have not been well understood. Using the reconstructed historical climate series, this study analyzed the teleconnection between the warm-season Arctic Oscillation (AO) and drought and flood (DF) in the UH and NNC at multi-temporal scales from 1650 to 1975. The results show that, with the transition of the AO on the inter-decadal and multi-decadal scales, the teleconnection between the AO and DF in the UH and NNC shifted accordingly. Overall, however, the DF in both areas changed in the same direction as the AO for most of the study period, i.e., when the AO index increased/decreased, the UH and NNC were more prone to drought/flood, and the frequency of extreme and severe drought/flood events tended to increase/decrease. The phase change in the correlation between the AO and DF in the UH and NNC has an influence on the transition between positive and negative correlations of DF in these two areas. Both the AO and the DF in the UH and NNC have inter-annual cycles of around 3–6 years, inter-decadal cycles of around 12 years, and multi-decadal cycles of around 20–30 years. Primarily on the multi-decadal scale, the AO is likely a significant predictor of DF in the UH and NNC. Furthermore, when the AO index abruptly increases/decreases, the UH and NNC are more prone to drought/flood than before.