岷江上游水文气象因子多尺度周期性分析

Multiresolution and periodicity analysis of hydrological and meteorological factors in upper reaches of Minjiang River

采用Dmey小波变换法对岷江上游杂谷脑流域1959年至2006年月径流量、月平均气温和月降水量不同时间尺度下的变化周期进行分析,探讨三者在长时间序列周期性变化中的相互响应,并根据主周期预测未来气温、降水和径流的变化趋势,结果表明:气温、径流和降水存在多尺度周期性变化,在不同的尺度周期中,表现出不同的冷暖、丰枯和干湿的振荡规律,总体表现为由小尺度无明显规律的剧烈振荡向大尺度有明显规律的振荡变化。3个要素同以8—12个月的小尺度为周期剧烈振荡,在较大时间尺度上,具有明显规律振荡变化的周期分别为气温500个月、径流150个月和降水120个月。受森林砍伐的影响,研究区域在1962—1988年期间径流对降水变化的周期性响应迟钝,而在1988—2006年期间基本同步。根据大尺度周期性波动趋势预测,未来十几年研究区域处于偏暖的年代际背景下,未来6—7a为多雨期,但径流量偏少。

In this study,the Dmey transformation approach was used to analyze monthly runoff,mean temperature,and precipitation from 1959 to 2006 in the Zagunao basin in the upper reaches of the Minjiang River,to explore the mutual responses to periodic changes in these three variables and to attempt to predict the trends of future temperature,precipitation,and runoff. This study is focused on dynamic-change mechanisms of runoff on a large scale,and should provide helpful insights into water management and control of soil water losses in the Zagunao watershed. The results showed that temperature,runoff,and precipitation changed periodically in several scales,and the oscillation raw data on cold and warm temperatures,plentiful and scarce runoff,and wet and dry periods differed. Overall,the presentation changed from nonobvious regular violent oscillation on a small scale to obvious regular oscillation on a large scale. All three elements showed the small-scale periodic violent oscillation of 8 to 12 months. On a larger time scale,the periods of obvious regular oscillation of temperature consisted of 500 months,and the runoff 150 months,the precipitation 120 months. The Zagunao watershed is characterized by high average elevation,low annual average temperature,and a prolonged snow cover. The percentage of the snow area is 3. 53% at the end of June. Therefore,snow melting is a hydrological process that must be taken into account in this area. Temperature is the main factor that influences snowmelt runoff. The latter might be the main reason for the differences between this study and others. Because the Zagunao watershed belongs to an alpine region that hasa short spring season,the characteristics of temperature and precipitation in the spring are similar to those of winter.November to December and January to April are nongrowth seasons. The precipitation types are dominated by snow,which should undoubtedly have an impact on the dynamic and periodic changes of runoff,thereby resulting in periodic variation,which is different from that in a low-elevation area. From 1962 to 1988,the periodic response of runoff to precipitation changes was insensitive,but it changed and became synchronized with precipitation from 1988 to 2006. Deforestation and vegetation that were damaged in the study area between 1962 and 1978,as well as the low-frequency oscillation of runoff,might have resulted in soil drought and a reduction in soil water. The high-frequency oscillation of runoff was the reflection of the periodic changes in surface runoff. The intra-annual variation and interannual high-frequency oscillation of runoff in this area were caused by variation of precipitation. The focus of this research was the dynamic mechanisms of these three hydrological and meteorological factors on a large scale. Ecological and hydrological processes on a large scale showed better predictability and regularity. Some local heterogeneity and nonlinearity on a small scale are expected to be smoothed out on a large scale. According to the trend of large-scale periodic fluctuation,the study area should be in a warmer background era in the coming decades,and the precipitation is expected to be plentiful in the next 6—7 years; in contrast,the runoff is expected to be scanty.