Variation of Precipitation and Streamflow in the Upper and Middle Huaihe River Basin, China, from 1959-2009

Variation of precipitation and streamflow in the Upper and Middle Huaihe River Basin (UMHRB) during 1959-2009 is characterized in this study with the Mann-Kendall (MK) test and Sen's slope estimator. The rotated empirical orthogonal function (REOF) was selected to obtain the sub-basins over UMHRB. The cumulative sum of departures of modulus coefficient (CSDMC) was used in this study to detect the temporal variability of streamflow and precipitation. The results are drawn as follows: (1) Four sub-basins were obtained by REOF: Region I: northern UMHRB, Region II: southern UMHRB, Region III: western UMHRB and Region IV: eastern UMHRB. (2) For precipitation, noticeable wet/dry seasonal shifts in UMHRB can be found: the wet tendency in summer and winter and dry tendency in spring and autumn. The northern (Region I) and southern (Region II) UMHRB were more significant than other two parts. For streamflow, measurements at stations in the northern UMHRB showed downward trends for all four seasons, especially, for spring and autumn. Although precipitation of the northern UMHRB showed upward trends in summer and winter, the streamflow trends were downward. (3) Precipitation and streamflow of the most stations in UMHRB exhibited a close correlation. However, the correlation coefficients of the linear regression models of Fuyang and Zhoukou for locations in the northern UMHRB were lower than those of the other five stations. The runoff decreased faster than precipitation in Fuyang, Zhoukou, and Jiangjiaji since 1980, which trend has become significant after 1990. (4) Streamflow variability in the northern part showed a negative direction in the most years, especially after 1985 and partly influenced the streamflow variability in Bengbu and Lutaizi located in the downstream of UMHRB. The observed downward trend of actual evapotranspiration should slow down the downward runoff trend. However, the results indicate that since 1980 the runoff patterns in the northern and southern UMHDRB have exhibited declining trends, which became strongly manifested since 1990, with the streamflow reduction being mainly attributed to human activities. The results obtained are instrumental in getting a deeper insight into precipitation and flow variations in the northern and southern parts of China since the investigated basin is a transition zone between them.