Hail hazard on a reference area of 100m2: hail size with 50-year return period

The hail hazard maps show statistically estimated return values of the hailstone size LEHA-100 for the 50-year return period. LEHA-100 describes the largest hailstone size to be expected on a reference area of 100 m2. It is derived from the radar algorithm MESHS, which is the size of the maximum expected hailstone per square kilometre (radar data from MeteoSwiss for 2002 to 2020). The new hail hazard maps represent the hailstone size as a function of the return period T. They describe the hailstone size that is exceeded under current climate conditions, per reference area, with a probability of 1/T per year. Thus, the map for 50 years shows which hail size is to be exceeded on the long term on average once in 50 years or with a probability of 2% per year. These maps provide an updated basis for assessing the local hail hazard. The map of hail zones in Annex G1 of the standard SIA 261/1 (2020) remains valid. MESHS: Maximum Expected Severe Hail Size is defined as the maximum expected hail size per square kilometre. This means that most of the hail stones in this area of one square kilometre are smaller. LEHA: Largest Expected Hail on a reference Area is a mathematical derivation from the hail size MESHS, which refers to an area of one square kilometre. LEHA describes the largest expected hail size that can be expected on a smaller reference area. In extreme cases, a hail stone of size MESHS can occur on the smaller reference area, but this will rarely happen. DOI: https://doi.org/10.18751/Climate/Griddata/CHHC/1.0本冰雹灾害图呈现了针对50年重现期的冰雹尺寸LEHA-100（Largest Expected Hail on a 100 m² Reference Area，100平方米参考区域最大预期冰雹尺寸）的统计估算重现值。LEHA-100指的是在100平方米参考区域内可预期的最大冰雹尺寸。该指标源自雷达算法MESHS（Maximum Expected Severe Hail Size，最大预期强冰雹尺寸），MESHS被定义为每平方公里内可预期的最大冰雹尺寸，其数据来源为瑞士气象局（MeteoSwiss）2002年至2020年的雷达观测资料。 本次更新的冰雹灾害图将冰雹尺寸表征为重现期T的函数，即当前气候条件下，每参考区域内超出该尺寸的冰雹每年发生概率为1/T。因此，50年重现期对应的灾害图展示了长期平均每50年出现一次、或每年发生概率为2%的超出阈值的冰雹尺寸。本系列灾害图为局地冰雹灾害风险评估提供了更新后的依据。瑞士标准SIA 261/1（2020版）附录G1中的冰雹分区图仍然有效。 MESHS被定义为每平方公里内可预期的最大冰雹尺寸，这意味着该平方公里区域内的绝大多数冰雹尺寸均小于该阈值。LEHA（Largest Expected Hail on a Reference Area，参考区域最大预期冰雹尺寸）是基于每平方公里尺度的冰雹尺寸MESHS推导得到的数学指标，其表征的是更小参考区域内可预期的最大冰雹尺寸。极端情况下，该小参考区域内可能出现尺寸达到MESHS阈值的冰雹，但此类情况极为罕见。 DOI: https://doi.org/10.18751/Climate/Griddata/CHHC/1.0