黄河源区基流量的变化规律及影响因素

选用改进的加里宁方法计算出源区的基流量,利用小波变换、小系数方差等方法分析了1955—1999年基流量周期变化规律,同时利用显著周期振幅的不稳定性,计算同周期基流量与气象要素的小波系数的相关系数,判定了基流量变化趋势及显著周期的气象成因,确定了三次断流的原因。计算结果表明:源区基流量存在一个强趋势项、7~8a与3~4a两个显著周期。强趋势项决定了基流量的总体变化规律。受其影响,20世纪50年代以来,源区基流量呈现枯—丰—枯的变化规律。强趋势项与两个显著周期的叠加是基流丰枯变化的本质,是历史上三次断流的根本原因。计算结果还表明,基流量的强趋势项为气温所致,两个显著周期为降水所致。源区植被覆盖率与基流指数成负相关关系,当植被覆盖率增加20%时,基流指数将减少10%以上。

Periodic regularity of the base flow in the headwater region of the Yellow river and affecting factors

The headwater region of the Yellow river has become an excellent place for the study of alpine eco-hydrology and eco-environmentology for a series of serious eco-environmental deterioration problems occurring in the last two to three decades. The current study of the periodic regularity and affecting factors of the base flow, would be greatly beneficial to the understanding of the periodic regulation of the groundwater and the causes of the environmental degradation. Using the 1955-to-1999 runoff data measured at the Huangheyan hydrological station, we separate out the base flow by using the Kalinin method. Then the tendency and the periods of base flow are analyzed by employing wavelet transformation and variance of wavelet coefficient, respectively. The tendency of the base flow and the causes of the periodicity of the base flow and of the three-time-break runoff are also analyzed based on the correlation of the wavelet coefficient of the base flow and the meteorologic factors. The results indicate that there is a strong tendency and two significant periods, 3-4 year and 7-8 year with variable amplitudes in the base flow. The tendency with most intensive amplitude dominates the whole tendency of the base flow and induces the base flow changing from low-to-high-to-low. The strong tendency combined with the two significant periods result in the variation in the base flow including three breaking-flows from 1955 to 1999. In addition, the results based on the correlation of wavelet coefficient show that the tendency is determined by the same strong tendency of temperature, while the precipitation contributes to the two remarkable periods of the base flow. The base flow is negatively correlated with the vegetation coverage, that is, a rise of 10% in vegetation coverage would lead to a decrease of 20% in base flow.