Hazard assessment and regionalization of snowstorms in Heilongjiang Province from 1961 to 2015

Hazard risk has become an important issue because global warming will lead to an increased risk of extreme weather and climate events. Based on the daily snow precipitation of 63 cities and counties in Heilongjiang Province, China from 1961 to 2015, the probability of each level of snowstorm was calculated based on information diffusion theory, and a hazard index model was established using snowstorm probability and the amount of snow precipitation as two hazard-inducing indicators of snowstorm. Next, hazard assessment and regionalization of snowstorms was performed for Heilongjiang Province from 1961 to 2015. The results showed that under the background of global warming, the probability of moderate snowstorm, heavy snowstorm, and severe snowstorm in Heilongjiang Province increased over time. There was a particularly significant increase for moderate snowstorms at a rate of 20%/10a; moderate snowstorms, heavy snowstorms, and severe snowstorms had a 3-year, 4-year, and 11-year return period, respectively. The precipitation level of each snowstorm increased over the decades especially for the precipitation in moderate snowstorms (29 mm/10a). The precipitation of each level of snowstorm has increased significantly since the beginning of the 21st century. In addition, the hazard of each level of snowstorm and the comprehensive hazard of snowstorms all increased significantly with time; the most rapid increase was due to heavy snowstorms at a rate of 0.65/10a. The comprehensive hazard of moderate snowstorms increased at a rate of 1.46/10a. The comprehensive hazard of snowstorm was the highest in the southeast of Heilongjiang followed sequentially by the west and the central region. The hazard of each level of snowstorm was high in the southeast and lowest in the northwest for moderate snowstorms and heavy snowstorms. There were high hazards for severe snowstorms in the northwest. The light-/low-risk areas of all levels of snowstorm were concentrated in the central region. The probability of moderate and heavy snowstorms was the highest in the southeast region followed by the northwest and the central region. The precipitation from moderate and heavy snowstorms was the highest in the southeast followed by the central region and the northwest region. For severe snowstorms, there was a difference in the distribution between the probability and the precipitation, i.e., the probability was the highest in the northwest region, followed sequentially by the southeast and the central regions. The precipitation was relatively high in the southeast and northwest regions but low in the central and northern regions. The distribution of the probability, precipitation, and hazard of each level of snowstorm as well as the distribution of the comprehensive hazard all had the following patterns: The high-value areas gradually expanded with decades while the low-value areas gradually shrank. For the comprehensive hazard of snowstorm, the high-risk areas increased by 30.7% from 1960s to 2010s as opposed to the 38.9% reduction of low-risk areas. In particular, the high-hazard and low-hazard areas of heavy snowstorms underwent the largest changes over the decades with the former increasing by 37.4% and the latter decreasing by 28.5%.