A study on the annual runoff change and its relationship with water and soil conservation practices and climate change in the middle Yellow River basin

Based on the long-term hydrological and meteorological series. DEM, soil database and documents of soil conservation measures of the middle Yellow River, investigations are made on the spatial and temporal changes of runoff and the impact of 11 factors, which include rainfall, temperature, terrain slope, drainage density, gravel, sand, silt, and organic carbon content in soil, water consumption, and soil conservation measures. The results show that the total runoff generated from the middle Yellow River had a decreasing trend in the past 60 years, with two abrupt falls around the years 1971 and 1991. In the spatial dimension, runoff modulus grew from the north to the south and from the west to the east, and the largest gradient of spatial change of runoff modulus happened during the period of 1956-1970 before the first falls of the total runoff. In the period 1954-2009. the average annual rate of temporal change of runoff modulus increased acceleratedly outward from the northwest of the middle Yellow River with a concentric ring pattern. Correlation analysis of runoff modulus with potential influencing factors in the spatial perspective reveals that the spatial distribution of the runoff modulus is principally the results of the regional variation of natural conditions. The results of the correlation analysis of the temporal series of runoff coefficient and influencing factors suggest that climate change, hydraulic engineering and soil conservation measures, were all the major causes of runoff reducing in the second half of the last century in the middle Yellow River. For the whole middle Yellow River, climate change contributed over 40% of the runoff deviations in the 1960s, 1970s and 1990s. while water consumption induced also over 40% runoff reduction in the 1960s. 1970s and 1980s. The runoff reduction due to hydraulic engineering was about 2-3 times of that caused by soil conservation measures, and both of them increased continuously from the 1960s to the 1980s, and kept at a higher level in the 1990s. The contribution of different causes to runoff deviation was variable in different drainage areas. Generally, in the semi-arid areas climate change played a decreasing role in runoff reduction comparing with other causes, while in the semi-humid areas it induced a higher and more variable proportion of runoff deviation according to the decade means. (C) 2012 Elsevier B.V. All rights reserved.