基于Copula函数的河北省夏大豆干旱风险特征研究

Study on drought risk characteristics of summer soybean in Hebei Province based on Copula function

干旱是河北省夏大豆生育期内的主要农业气象灾害之一。选用1991-2020年河北省夏大豆种植区97个气象站的气温、降水、日照时数、风速等资料,以作物水分亏缺距平指数划分干旱等级,基于游程理论提取干旱事件的历时和烈度,采用Copula函数分析干旱事件的同现重现期,以及干旱事件同现重现期与大豆单产之间的关系。结果表明:(1)该区干旱历时、干旱烈度的高值区位于邢台、邯郸,干旱频次的高值区位于石家庄西部、保定西部、廊坊北部,说明高频次的区域不一定是长历时、强烈度干旱过程的分布区域。(2)河北省夏大豆干旱历时以威布尔分布和对数正态分布为主,而干旱烈度以广义极值分布和对数正态分布为主。(3)Frank-Copula函数为河北夏大豆干旱历时和干旱烈度的最优联合分布函数。(4)时长为3旬的干旱事件重现期最小,重旱的高风险区主要分布在廊坊、保定、石家庄中西部、沧州中东部、衡水、邢台、邯郸;时长为11旬的各等级干旱仅邯郸中东部为相对高风险区,其它大部地区为低风险区,即时长为11旬的干旱事件出现的可能性较小。(5)大豆单产与干旱时长、干旱烈度的相关系数75%的站点通过了P<0.05的显著性检验,与重现期的相关系数所有站点均通过了P<0.05的显著性检验,甚至1个站点通过了P<0.001的显著性检验,说明重现期更能反映干旱事件对产量的影响,长历时、高烈度干旱事件的重现期低值区为干旱的高风险区。

Drought is one of the main agro-meteorological hazards in the growth period of summer soybean in Hebei Province.Based on the observed meteorological data of 97 weather stations in the summer soybean planting area of Hebei Province from 1991 to 2020 and the crop water deficit index,the duration and intensity of drought events were analyzed by the runs theory,and the recurrence period of drought as well as its relationship with soybean yield were studied by the Copula function.The results showed that:(1)The high value area of drought duration and drought intensity in this area was in Xingtai and Handan,and the high value area of drought frequency was in the west of Shijiazhuang,west of Baoding and north of Langfang,indicating that the area of high frequency was not necessarily the distribution area of long duration and intense drought process.(2)The marginal distribution function with the largest number of sites for drought duration was Weibull and lognormal,and for drought intensity was generalized extreme value and lognormal.(3)According to the goodness-of-fit test of the root mean square error,the optimal joint distribution function of drought duration and intensity was the Frank-Copula function.(4)The recurrence period of drought events in 3 ten-days was the smallest,and the high-risk areas of severe drought were mainly distributed in Langfang,Baoding,the middle west of Shijiazhuang,and the central and eastern of Cangzhou,Hengshui,Xingtai,and Handan.All levels of drought in 11 ten-days were relatively high-risk areas,while most other areas were low risk areas,and the possibility of drought events in 11 ten-days was less.(5)The correlation coefficient of soybean yield and drought duration and drought intensity of 75%passed the significance test of 0.05,and the correlation coefficient of the recurrence period of 0.05.Even one site passed the significance test of 0.001,indicating that the recurrence period better reflected the influence of drought events on yield,and the recurrence period of low value of long duration and high intensity drought events was the high-risk area of drought.