Abstract:

The Songnen Plain is an important commercial grain base and wetland distribution area in China, and the evolution of dry and wet events is closely related to regional food security and ecological safety. Based on the daily meteorological data including temperature, precipitation and wind speed from 36 meteorological stations in and nearby the Songnen Plain, the monthly surface wetness index of each station was calculated by the Penman-Monteith equation, and the frequency of extremely wet and dry events was further calculated after standardization. Then, the trend analysis and Kriging interpolation method were used to explore the spatiotemporal evolution characteristics of extremely dry and wet events, and the squared wavelet coherence spectrum was adopted to detect the potential annual-scale correlation between the extremely dry and wet events and the Oscillation indexes. The results showed that: (1) annual extremely dry events occurred frequently in the Songnen Plain from 1960 to 2020, with an average value of 7.86 times in the past 60 years, while annual extremely wet events were less frequent; the annual extremely dry event frequency showed an obvious decreasing trend and the annual extremely wet event frequency showed an increasing trend, with the climate tendency rate of -0.10 times/10 a and 0.02 times/10 a, respectively; (2) spatially, the frequency of extremely dry events in most areas of the Songnen Plain was not significantly weakening, while the frequency of extremely wet events was low and the trend was obviously increasing in the east and decreasing in the west; (3) the evolution of dry and wet events in the Songnen Plain was closely related to the Oscillation index, the annual frequency of extremely dry events was positively correlated with the Arctic Oscillation index, the Atlantic North American Oscillation index and the North Atlantic Oscillation index; however, the annual frequency of extremely wet events was mainly negatively correlated with them; in addition, the relationship between the extremely dry and wet events and the Southern Oscillation index exhibited obvious differences on interannual and interdecadal scales; (4) the evolution of the frequency of extremely dry and wet events was closely related to the regional socio-economic sector water consumption, which affected regional water security. This study could provide support for water resource planning and management of the agricultural-wetland system in the Songnen Plain to adapt to climate change.

Key words: Songnen Plain, extremely dry/wet events, humid index, spatiotemporal evolution, Oscillation index