Lu Qiyao
Accumulated temperature above 10℃(Σt) and annual minimum temperature(Tm) are the major indexes for demarcating agroclimatic zones. The return period(τ) of Σt and Tm and the shift of Σt-and Tm-isopleths with τ are calculated. 1. According to the magnitude of shift of Σt-and Tm-isopleths, in northeast China, Inner Mongolia and north Xinjing the fluctuation of heat resources in growing season from year to year is the greatest and strongly influences the yield of annual thermophilous crops but in the Changjiang River basin the fluctuation of the low temperature in winter is the greatest and seriously injures the perennial subtropical tree crops. 2. In the anomalous cool summer year with τ=30, the northern boundaries of the southern subtropical, northern subtropical and warm temperate zones and the southern boundary of the frigid temperate zone in China could be expected to shift southward 150, 220, 250 and 300km from their normal positions, respectively. 3. In the anomalous cold winter year with τ=30, the northern boundaries of the tropical,southern subtropical, northern subtropical and warm temperate zones, and the southern boundary of the frigid temperate zone could be expected to shift southward 270, 150, 450, 290 and 350km from their normal positions, respectively, and the extremely low temperature seriously injure not only the subtropical tree crops in the Changjiang River basin as mentioned above, but also the tropical crops in South China,even Hevea brasiliensis in southern Yunnan.
