基于1971—2016年陇中黄土高原半干旱区逐日地面最低温度资料,采用气候统计学方法,研究了霜冻初、终日和无霜冻期时空变化、异常分布特征。结果 表明:研究区域最早霜冻初日为8月25日; 最晚霜冻终日为6月28日; 平均无霜冻期125～149 d。近46 a来,研究区域霜冻初日呈推迟趋势,平均每10 a推迟3.1 d,无霜冻期显著延长,平均每10 a延长3.9 d。无霜期日数显著延长,增加了作物生长季热量条件,有利于作物生长季延长,使得喜温和越冬作物适宜种植区域由低海拔向高海拔区域推进。冬小麦、玉米适宜区、可种植区扩大; 春小麦适宜种植区、不可种植区缩小; 农作物复种指数明显增加,但霜冻波动的不稳定性变化增加了低温冻害的风险。
The spatiotemporal change and abnormal distribution characteristics of the earliest day and the latest day of frost as well as the frost-free period were studied by a climatic statistical method based on the daily lowest ground temperatures in semiarid regions of the Loess Plateau in Central Gansu during the period 1971—2016. The results show that the earliest frost day are August 25, the latest frost day is June 28, and the mean frost-free period is 125～149 days in the research area; in recent 46 years, the earliest frost day has been postponed by 3.1 days per daceade, and the frost-free period has been significantly prolonged by 3.9 days per decade. The prolongation of frost-free period increased the heat in the crop growth season and was benefitial to crop growing, and thus the planting areas suitable for thermophilic crops and winter crops were expanded from low altitude to high altitude. The areas of winter wheat and maize expanded; the areas of spring wheat and the areas not suitable for planting crops shrank; and the multiple cropping indexes were significantly improved. However, the instable variation of frost has amplified the risk of low temperature and frost-induced damage.
