黄河流域日照时数变化趋势分析

Variation of Sunlight Radiation Duration in the Yellow River Basin

本文利用非参数统计检验方法(Mann-Kendall法)分析了黄河流域77个气象站1958年～2001年日照时数序列的长期变化趋势,并用参数检验法对其结果进行了相互验证.结果表明,黄河流域1958年～2001年的年、典型月日照时数序列均大致存在一定的下降趋势,年序列所选77个站中有53个表现出下降趋势,只有24个表现出一定的上升趋势;在有意义(拒绝零假设)的34个站点中,28个站点表现出下降趋势,6个显示出上升趋势.为了进一步阐明日照时数长期变化趋势的时空分布特点,根据研究区的气候特点,将黄河流域分为5个子区域.结果表明子区域Ⅰ,Ⅱ和Ⅲ的日照时间均表现出了明显的下降趋势,但这一趋势在子区域Ⅳ和Ⅴ表现并不明显.这一结果说明在过去的40年到50年期间,黄河流域的日照时间总体上呈下降趋势,这一趋势在黄河流域中下游地区尤其明显.在此基础上,选择1月、4月、7月和10月作为一年四季的代表时段,对日照时数的时间分布特点进行了分析.其结果表明,对年日照时数下降趋势贡献最大的月份是1月、6月、10月和12月;日照时数的长期变化趋势既存在一定的时间差异,也存在着一定的地区差异.

The Mann-Kendall statistic test is a rank-based non-parametric method, which has been widely used to detect trends in hydro-meteorological time series such as streamflow, temperature, precipitation and sunlight radiation hours, etc. Sunlight radiation duration is one of the important climatic factors. The possible trend of annual and monthly sunlight radiation duration in the Yellow River basin was detected by using the Mann-Kendall test in this paper. The data used in this study were observed at 77 meteorological stations in the Yellow River basin. The Mann-Kendall test was applied to annual and monthly time series from 1958 to 2001. At the same time, a parametric test was also applied to make the trend analysis. The results shown that there is an obvious downward trend in the annual and monthly sunlight radiation durations in the subregion of Ⅰ , Ⅱ , and Ⅲ , but subregion of Ⅳ and Ⅴ did not exhibit significant long-term trend. The results from 53 stations shown a decreasing trend and only 24 stations exhibited an increasing trend. 34 stations rejected the null hypothesis, among which 28 stations shown significant decreasing trend, and only 6 stations shown significant increasing trend. In other words, most area of the middle and downstream of the Yellow River basin exhibited downward trend of sunlight radiation duration, but the upstream did not show obvious long-term trend. This demonstrated that decreasing trend dominated the long-term trend of the sunlight radiation duration in the study area during the past fifty years. On the basis of above analysis, January, April, July, and October were selected as typical months to represent four seasons of the year, and the corresponding long-term trend for these representative months were further investigated. The results shown that in January, June, October and December there is a greater long-term trend and a greater contribution made by annual sunlight radiation duration. The temporal and spatial distribution of the long-term trend for the sunlight radiation duration in the study area shows that there is a difference for the trend of sunlight radiation duration over different area during different periods in the Yellow River basin from 1958 to 2001.