苹果花期冻害气象指标和风险评估

花期冻害是影响苹果产量和品质形成的主要气象灾害之一。基于苹果花期冻害发生的地理分布、气象背景数据和已有研究成果，利用最大熵模型和ArcGIS空间分析工具，筛选出影响苹果花期冻害发生分布的暴露性指标和主要致灾气象因子，利用全国1981—2013年2084个气象站资料，评估了苹果主产区花期冻害的风险。结果显示:苹果花期冻害发生的暴露性指标是花前日最高气温大于等于6℃有效积温为420~550℃·d，主要致灾气象因子和高风险阈值按照贡献率大小依次为冻害过程的最大日较差 (大于等于22℃)、极端最低气温 (小于等于-2℃)、降水量 (小于等于5 mm) 和日最低气温小于等于0℃积温 (小于等于-14℃·d)。花期冻害风险较高的区域位于北疆、黄土高原西部和北部及川西高原区，而环渤海湾和黄河故道产区风险相对较低。不同风险区的分布与各地苹果物候期差异和春季冷空气的活动路径有关。

Meteorological Disaster Index and Risk Assessment of Frost Injury During Apple Florescence

Frost injury during the florescence is one of the most serious meteorological disasters affecting the production and quality of apple. In temperate regions, effects of frost damage on deciduous fruit trees during florescence exceed effects of winter freeze. The risk of frost injury in the apple florescence depends on the developmental stage and disaster-causing factors. The minimum temperatures or frost days are usually adopted as disaster-causing factors, but single index cannot reflect combined effects of meteorological factors on frost injury.The disaster exposure index and the dominant disaster-causing factors are determined based on the geographical distribution of frost injury during the apple florescence, meteorological data, together with the maximum entropy (MaxEnt) model and ArcGIS spatial analysis technique. An assessment is carried out on the main cultivated area using meteorological data from 2084 meteorological stations during 1981-2013. Results indicate that the frost injury occurs when the effective accumulated temperature (daily maximum air temperature is no less than 6℃) reaches 420-550℃·d before flower-beginning. The dominant disaster-causing factors and their thresholds to the frost injury in influence descending order are listed as follows: The maximum diurnal range of temperature (no less than 22℃), the extreme minimum temperature (no more than-2℃), the precipitation (no more than 5 mm) and the accumulated daily minimum temperature below 0℃ (no more than-14℃·d) in processes of strong cold air. The higher risk areas include northern Xinjiang, western and northern Loess Plateau, especially the plateau area of the western Sichuan, while risks in areas around the Bohai Bay and the Old Course of the Yellow River are lower. The distribution of risk areas are related with the apple phenophase and routes of cold air. The disaster affected degree also varies according to different cultivars.