青海省冰雹灾害分布特征

根据青海省近40年冰雹灾情统计资料,研究了青海省雹灾发生频数及受灾面积、成灾率的时空分布特征。结果表明:雹灾发生频数自20世纪60年代逐渐上升,80年代出现高峰值,90年代后有逐渐减少的趋势。青海省冰雹灾害发生的时间为5~10月,6~8月最多,属夏季多雹区类型;东北部区占总雹灾频数的86.35%,成为全省雹灾高峰区;但是雹灾高峰区与冰雹发生高值区并不一致。雹灾面积也呈逐年上升的趋势,与全省雹灾发生频数的变化趋势基本一致;各区平均受灾面积与成灾率有月际变化,东北部区平均受灾面积7月达到最大值,成灾率9月达到最大值;青南区受灾面积最大值出现时间与东北部一致,成灾率最大值出现在7月。形成雹灾的冰雹直径出现频数最多在20~30 mm之间,受灾面积随冰雹直径的增大而增加,成灾率也随之增大;冰雹直径超过40 mm后,对作物的危害是毁灭性的。

Distributional Characteristics of Hail Disasters in Recent 40 years over Qinghai Province

According to the hail data of the recent 40 years(from 1962 to 2002) over Qinghai Province,the temporal-spatial distributional characteristics of the hail disaster occurrence frequency,disaster area,and disaster rate are studied. The result shows: The frequency of hail disaster occurrence increased gradually from the 1960s,reached the peak in the 1980s,and decreased gradually from the 1990s.Hail disasters occurred in Qinghai Province from May to October,mostly in June,July and August.The hail disasters occurred in the northeastern part accounts for 86.35% of total hail disasters.The high-frequency hail disaster area did not overlap with the high-frequency hail event area.The hail disaster area increased gradually also over the whole province,basically in agreement with the tendency of the hail disaster occurrence frequency.There is intermonthly variation in the average disaster area and disaster rate for all parts of Qinghai Province,with the maximums of the disaster area and disaster rate in July and September in the northeastern Qinghai,and those of both disaster area and disaster rate in July for the southern Qinghai.The diameters of hailstones inducing disasters appear between 20 and 30 mm mostly.Both disaster area and disaster rate increase with the increasing hailstone diameter.When the diameters of hailstones exceed 40 mm,crops will be damaged destructively.