Long-term trend of precipitation in the Yellow River basin during the past 50 years

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Some of previous studies showed that the drying-up of the lower Yellow River was resulted from decreasing precipitation and excessive industrial and agricultural consumption of water from the middle and lower Yellow River.The analysis for the long-term trend of precipitation is helpful for the rational use of water resources in the Yellow River basin. The Mann-Kendall statistictest is a rank-based,non-parametric approach and has been widely used to estimate the significance of long-term trends in the hydro-meteorological time series such as water quality,streamflow,temperature,and precipitation.The long-term trend of precipitation in the Yellow River basin was analyzed in this paper and the Mann-Kendall test was applied to annual and monthly precipitation time series.The linear regression was compared with the results obtained by using Mann-Kendall test.The results show that 65 of 77 stations exhibited downward trend for annual precipitation.April,July and October contributed the most of the decreasing trend of annual precipitation,and the spatial distribution of long-term trend for typical months is different.In all months except January,February,March and June,the values of trend are negative,exhibiting the decreasing tendency.In all seasons except summer,there is a similar increasing trend in the upstream of the Yellow River,south of the northern latitude 35 degrees.Except the regions in the upstream of the Weihe River and Hohhot the precipitation showed a decreasing trend in the Yellow River basin,especially in the downstream of the Yellow River.Comparing the results estimated by two methods,the Mann-Kendall test and linear regression test,the stations in winter(from December to next February),without trend tested by Mann-Kendall method,are much more than those tested by linear regression method,and the number of stations with trends tested by both methods is similar in other seasons.The magnitude of trend estimated by both methods is also similar in all months except July and December,and the absolute values of trend estimated by linear regression method are greater than those estimated by Mann-Kendall method.