利用MCI指数和Gumbel-Copula函数评估新疆干旱灾害危险性

Assessing drought disaster hazard in Xinjiang of China using MCI and Gumbel-Copula function

干旱是新疆地区的主要气象灾害之一,其危险性评估对该地区防旱抗旱工作具有重要的指导意义。该研究基于新疆106个气象站1961—2019年逐日观测数据计算气象干旱综合指数(meteorological drought composite index,MCI),根据游程理论识别干旱过程,采用Gumbel-Copula函数建立干旱历时和烈度的联合分布并计算干旱重现期;选取干旱频次、历时和烈度作为危险性评估因子,采用随机森林算法计算权重并得到新疆干旱灾害危险性结果。结果表明:1961—2019年间新疆共出现了47次干旱过程,其中短历时、低烈度(干旱烈度≤50且干旱历时≤60 d)干旱过程多发,长历时、高烈度(干旱烈度≥200且干旱历时≥180 d)重现期较长。长历时和高烈度倾向于同时发生,但随着干旱历时和烈度的增加,长历时和高烈度干旱过程发生概率较低。新疆地区干旱灾害危险性空间分布上呈现“中间低,南北高”的特点,天山山脉地区干旱重现期长于其他地区,危险性低,天山北坡的干旱过程发生频率低、持续时间短、强度小,危险性较低;南疆大部分地区的干旱过程发生频率较低,但持续时间长、强度大、危险性较高。而北疆大部分地区干旱发生频率高,但持续时间不长,强度不高,但塔城地区西北部和阿勒泰地区危险性较高。因此南北地区对干旱灾害应对应有所不同。在全球变暖背景下,新疆各地区用水矛盾进一步加剧,各地应结合实际,统筹提高水资源高效配置合理利用水平,合理开发水资源,降低干旱灾害的风险。

Drought is one of the major meteorological disasters in the world.It is urgent to accurately assess the frequency of drought events and the risk of drought disasters in the region,particularly for the warning,prevention and mitigation of regional damage.In this study,the MCI(meteorological drought composite index)was calculated using the daily observation data from the 106 meteorological stations in Xinjiang in western China during 1961-2019.The drought process was identified using the runs theory.The joint distribution of duration and intensity was also established to calculate the return period using the Gumbel-Copula function.Eventually,the hazard factors were taken as the frequency duration and intensity of drought events.The weights were calculated to assess the hazards of drought using the random forest.The results show that there were 47 drought events in the study area during 1961-2019.Among them,drought events with short duration and low intensity(intensity≤50 and duration≤60d)were frequent,whereas,the extreme drought events occurred less frequently with long duration and high intensity(intensity≥200 and duration≥180 d)tend to associtate with longer return periods.Long duration and high intensity tended to occur simultaneously.However,the probability of occurrence decreased with the increasing drought duration and intensity.The drought return period was longer along the Tianshan mountain range than that of other regions under the same duration and intensity conditions.The spatial distribution of drought hazards was performed as the middle low,and the high north-south ends.The hazard was much lower along the Tianshan Mountains.The drought events occurred less frequently on the northern slope,especially with the short duration and the low intensity.The higher hazards can be observed in most parts of the southern region.A similar trend was found in the northwestern part of the Tarbagatay Prefecture,as well as the central and northern of the Altay Prefecture in the northern region.There were different characteristics of drought,although the hazards were high in both the northern and southern regions.The drought events occurred less frequently,but lasted for a long duration with the high intensity in most stations in the southern region.However,the high frequency of droughts was found in the northern region,but for a short duration and low intensity.The northern and southern regions should respond to the drought disasters in different plans.An efficient drought early warning and monitoring system can consider the drought occurrences and development trends in the local conditions.Efficient allocation and utilization of water resources can then be balanced to reduce the risk of drought disasters.