基于EMD西安市虚拟水总量波动及其成因的时空多尺度分析

Fluctuation and causes of total virtual water in Xi'an City at multi-time and space scale based on empirical mode decomposition method

根据虚拟水相关原理方法,计算出西安1980-2014年主要农作物虚拟水,通过利用经验模态分解方法(EMD)分析了1980年以来西安市虚拟水总量的波动周期,指出其存在着3 a及10 a准周期的波动,并以10 a的周期波动为主,并从时空多尺度对西安市虚拟水总量波动周期的影响因素进行了分析。结果表明:从时间尺度来看,粮食总产量和作物虚拟水交替影响着西安市虚拟水总量准3 a周期的波动;西安市虚拟水总量准10 a周期左右的波动,在1990年以前主要受作物虚拟水影响,1990年以后受作物虚拟水和粮食总产量波动的交互叠加影响。对西安市三大区域进行EMD分解时发现,在短周期显示,西安市三大区域都是西安市虚拟水总量的主要控制区,其影响程度由高到低依次为:四郊县、远郊区和城六区;在长周期显示,远郊区和四郊县是西安市虚拟水总量波动的主要控制区,且远郊区是第一控制区。

As a case study of Xi＇an City,the virtual water and the total amount of virtual water were calculated using the meteorological data and data from statistical yearbook of Xi＇an from 1980 to 2014. By the means of EMD,the Empirical Mode Decomposition method,the influencing factors of total amount of virtual water were discussed and studied atspatio-temporal multiscale. Results show as follows：（1）The total amount of virtual water in Xi＇an showedan increasing trend expect for the year of 1982,1992 and 2014. There werea 3-year-cycle fluctuation and a 10-year-cycle fluctuation in the gross amount of virtual water,and the 10-year-cycle wasthe main fluctuation.（2）At the spatial-temporal multiscale,the 3-year quasi-cycle fluctuation of total amount of virtual water was affected by the grain yield and crop virtual water. The 10-year cycle fluctuation of total amount of virtual water was mainly affected by the crop virtual water before 1990 and the grain yield and the crop virtual water after 1990.（3）The study of three zones by EMD reveals that in short period,the three zones of Xi＇an City wereall the control areas of the 3-yearquasi-cycle fluctuation of Xi＇an city＇s total amount of virtual water;from high to low,the degree of impact ranked as： suburbs county,outer suburb district and the city six districts;in the long period,outer suburb district and suburbs county werethe major control areas of 10-year-cycle fluctuation of Xi＇an city＇s total amount of virtual water,and outer suburb district was thefirst control zone. The paper provides a better understanding of the water resource consumed by grain production in Xi＇an;it also facilitates a more scientific regulation of grain production;furthermore,it provides a reference for similar cities thatare short in water resource to mitigate the pressure on water resource and develop a strategy for grain production.