旱灾对粮食生产影响的非线性动态效应评估

自然灾害严重威胁粮食安全，因此科学地理解和认识自然灾害与粮食产量之间的关系至为重要。基于时变Copula函数方法的实证研究结果表明，水稻、小麦、玉米在低产时和旱灾的尾部相关系数分别为0.52、0.15、0.58，但是水稻、玉米在高产时和旱灾比率的尾部相关系数近似为0，小麦在高产时和旱灾的尾部相关系数仅为0？06，这意味着粮食单产与旱灾的关联性表现出非对称性。旱灾对粮食产量影响的时变性也因不同作物而异。对于水稻而言，随着技术水平的提高，旱灾与水稻单产的关联性存在显著的下降趋势；但是，旱灾与小麦、玉米单产的关联性并没有表现出随时间推移而下降的趋势。

Assess of Nonlinear Dynamic Effects of Drought on Food Production

Natural disasters deeply influence the security of the crop＇s production. It is critical for under-standing and recognizing the relationship between natural disasters and food production. The empirical results of time-varying Copula function method show that the tail correlation coefficient was respectively 0.52, 0.35, 0.58 between drought and rice, wheat, corn in low-yielding. However, the tail correlation coefficient was approximately zero between drought and rice, corn in high-yielding. The tail correlation coefficient was only 0？06 between drought and wheat in high-yielding. This means that the grain yield and drought correlation showed asymmetry. The results also showed that the time-varying impact of drought on grain yield depended on different crop. The dynamic correlation between drought and rice showed significant decline with technology improving. But the correlation between drought and wheat and maize did not show decline with time.