基于马尔科夫过程的珠江流域干旱特征研究

Research on Drought Behaviors in the Pearl River Basin Based on Markov Chain

对干旱转移概率的有效把握是干旱预报的关键,进而能够用于减轻干旱危害。基于此,根据Copula函数导出了马尔科夫链的转移概率矩阵。将干旱分为了6种状态,干旱事件和干旱状态不同,当干旱事件的严重程度不小于某一干旱状态时,在本文中就被定义为具有该严重程度的干旱事件。为了研究珠江流域的干旱特征,对某一严重程度干旱事件的平均历时、从任一干旱状态到没有干旱状态的平均首达时间、以及从没有干旱状态到某一严重干旱事件的平均首达时间进行了分析。研究结果表明:1非常极端干旱事件持续约1.5个月,轻微干旱事件持续约3个月;2从非常极端干旱状态恢复到没有干旱状态需要约3.5个月,从轻微干旱状态恢复到无旱情需要约1.7个月的时间;3一般来说,珠江流域平均0.5 a中有一次中等干旱事件,1 a中有一次严重干旱事件,1.5 a中有一次极端干旱事件,以及3.5 a中有一次非常极端干旱事件。此外,研究结果还表明,珠江流域东南部地区干旱风险较高,而该地区人口稠密、经济发达,特别是其中的珠三角地区,因而需要特别重视干旱风险。同时,珠江流域西部地区也是干旱风险较高的区域。

Deep understanding of transition probability behaviors of droughts is the key to forecast of droughts,and mitigation of drought hazards. In this case,the transition probability matrix of the Markov chain was derived by the Copula functions. Six drought status were classified in the study,drought event was different from drought status,and a drought event with the severity not less than a certain drought status had been considered as a certain severe drought. In order to investigate the drought behaviors in the Pearl River basin,the mean duration of a certain severe drought,the mean first passage time from any drought status to no drought status,and the mean first passage time from no drought status to a certain severe drought were analyzed in this study. The results of this study indicated that：（ 1） the exceptional drought event lasted about 1. 5 months,and the mild drought event lasted about 3 months;（ 2） it took about 3. 5months from the exceptional drought status to no drought status,while it took about 1. 7 months from the mild drought status to no drought status;（ 3） generally,and there was a moderate drought event average in 0. 5 years,a severe drought event in 1 year,an extreme drought event in 1. 5 years,and an exceptional drought event in 3. 5 years. Further,the results of this study indicated higher risk of drought in the southeast part of the Pearl River basin,and further works needed to be done to prevent or mitigate the drought hazards,as these regions were densely populated and economically developed,especially in the Pearl River delta. In addition,the west part of the Pearl River basin had also been identified as a region with a higher risk of drought.