Dry and wet combination dynamics and their possible driving forces in a changing environment

Abstract

Previous studies on dry and wet combinations had focused on their evolution characteristics in a single season (i.e. spring or summer), while the dynamics and driving forces between the adjacent seasons remain unsolved, which is important for water resources planning and management in a changing environment. To this end, the dry and wet events in adjacent seasons in the Yellow River Basin (YRB) were evaluated based on the standardized precipitation index (SPI), and the joint return periods of various combinations of dry and wet conditions under two scenarios (moderate and severe) were calculated using a copula function. The Mann-Kendall test was used to explore the joint return period dynamics with a 31-year sliding window. The Copula-based likelihood-ratio method and cross-wavelet transform were adopted to explore the driving forces of dry and wet combination dynamics. The results indicate that (1) spring-summer and summer-autumn are prone to continuous dry (wet) events, while the probabilities of the combinations of dry and wet conditions occurring in autumn–winter and winter-spring are almost the same; (2) continuous wet events frequently occur above Longyang gorge and below Huayuankou, while the Inner flow area is prone to continuous dry events; (3) the risk of dry and wet combinations with high frequency decreases, whereas the risk of compound events with low frequency increases; (4) the dependency structure dynamics of the SPI series between adjacent seasons show the strongest correlation with the El Niño-Southern Oscillation (ENSO), followed by the Arctic Oscillation and sunspot activities, implying that the ENSO has a dominant control on the dry and wet combination dynamics in the YRB. This study brings new insights into dry and wet combination dynamics and driving forces in a changing environment and provides a scientific basis for the sustainable utilization of water resources in the YRB.