Region-dependent meteorological conditions for the winter cold hazards with and without precipitation in China

Abstract

Cold hazard is one of the major meteorological disasters in winter. However, the meteorological conditions for the cold hazard events vary signi cantly with both the feature of the event and the region of occurrence. This study divided winter cold hazard events in China into three categories based on the daily gridded dataset of cold hazards from November 1980 to March 2020: events without wintry precipitation (hazardous low temperature, abrupt temperature drop, and/or freezing), with wintry precipitation only (hazardous sleet and/or snowstorm), and with both. The region-dependent multivariate meteorological conditions for each category of cold hazards are investigated using ERA5 reanalysis data. Results show that the surface air temperature (T 2m ) and its anomaly (T 2m _ anom ) are lower than climatology during cold hazards. But the difference in T 2m among provinces exceeds 30°C, and even for the same province, the difference among different categories of cold hazards exceeds 10°C. The region-and category-dependent differences of T 2m _ anom and daily temperature drop (∆T 24 ) are also large, about 5°C and 2°C d -1 , respectively. The Multivariate Empirical Orthogonal Function analysis has further been applied to not only the abovementioned temperature-related variables but also the precipitation-related variables (i.e., daily accumulated total precipitation, daily accumulated snowfall, and daily mean snow depth) in the middle and lower Yangtze River region, which reveals the event-mean state and spatial-temporal coupling evolution during the progression of the event for the selected key meteorological variables. The meteorological conditions for cold hazards put forward by this study could provide region-dependent and category-dependent reference for the prediction and warning of cold hazards.