| The study on the effects of climate change and human activities on the runoff and sediment of rivers is of great significance and value to the rational utilization and protection of water and soil resources and water and soil conservation projects in the river basin.Taking Donggou watershed in Chongli District of Zhangjiakou as the study area,this paper used cumulative anomaly method,Mann-Kendall non-parametric test method,moving average method,Morlet analysis method and double accumulation curve method to analyze the change characteristics of precipitation,runoff and sediment discharge and their future change trend during 2006-2018.The classification function of ENVI software was used to classify the land use types in Donggou watershed,and the land use transfer matrix,single and comprehensive land use dynamic degree and of Donggou watershed from 2006 to 2018 were obtained by combining with Arc GIS technology and Fragestats soft to explore the spatio-temporal change process and characteristics of land use and landscape pattern.Based on the double accumulation curve method and regression analysis method,the contribution rates of climate change such as precipitation and human activities including land use change to water and sediment change in the basin were studied.The main research conclusions are as follows:(1)Precipitation change: The annual average rainfall,flood season precipitation,summer precipitation,autumn precipitation and precipitation index of day(maximum daily precipitation and seven consecutive days maximum precipitation)of Donggou watershed are present the rising trend but not significant,the spring and winter precipitation showed the downward trend;The annual rainfall,flood season precipitation and summer precipitation,autumn precipitation index were plentiful from2013 to 2018,however the winter precipitation was plentiful in 2007-2018;Except for spring precipitation and autumn precipitation,which have no sudden change point,the sudden change points of other precipitation indexes are all from 2011 to 2013;There are two obvious cycles of annual precipitation,and the peak value is 2a and 7a,respectively,indicating that the annual precipitation changes are mainly periodic oscillations in small scales.(2)Land use change in Donggou watershed: Since 2006,the land use types in Donggou Basin are mainly forest land,cultivated land and shrub/grassland,and the total area of the three types in 2006,2010,2014 and 2018 accounts for 84.43%,92.62%,94.99% and 96.02%,respectively.Most of the forest land has not changed since 2006.From 2006 to 2010,the dynamic degree of land use was high,and there was a lot of mutual transformation among different land use types.From 2010 to 2018,the area change of each land use type was relatively small,and the dynamic degree of comprehensive land use was only half of that in duration of 2006-2010;.In Donggou watershed,urban and rural construction land,agricultural land and water area are mainly distributed in flat slope(0°-5°)and gentle slope(5°-15°)sunny slope area,while forest land,shrub/grassland are mainly distributed in incline(15°-25°)and steep slope(>25°)area,and most of them are in sunny slope having better hydrothermal conditions.Water area,urban and construction land,forest land and cultivated land all showed a trend of decreasing landscape heterogeneity,decreasing landscape fragmentation and good connectivity.However,due to the influence of human factors,the landscape fragmentation degree of shrub/grassland patches increased and the connectivity between patches became worse.(3)Variation of water and sediment in Donggou watershed: From 2006 to 2018,the runoff of Donggou watershed showed a slight upward trend,while the sediment discharge showed an obvious downward trend,and the inter-annual variation of runoff and sediment in the basin was relatively large.From 2006 to 2014,the runoff in the watershed was abundant,and after 2014,the runoff was in a dry period.From 2006 to 2008,the sediment was in a high-sand period,and from 2009 to 2018,the sediment was in a low-sand period.2013 is the abrupt change point of runoff from less to more,and there is no abrupt change point of sediment discharge in the same period.The results of periodic variation of runoff and sediment show that there are two cycles in the runoff,of which the time scale of6 a is the most periodic scale of runoff,and the scale of the periodic change of sediment discharge is 16 a,and the cycle is much larger than that of runoff.(4)The correlation between precipitation,land use pattern index and water and sediment in Donggou Basin : The correlation between annual runoff,annual sediment transport and precipitation、land use type area was not significant(P>0.05);The correlation between runoff and landscape pattern index is not significant,while NP and PD index are positively correlated with sediment discharge,while AI is negatively correlated with sediment discharge.(5)Impact assessment of precipitation and land use change on runoff and sediment: The dual cumulative analysis of precipitation and runoff and sediment in the Donggou watershed shows that human activities such as land use change are the main reasons for water and sediment change in the Donggou Basin from 2006 to 2018.Taking 2006-2009 as the base period,the contribution rates of human activities such as land use to runoff and sediment discharge from 2010 to 2014 are 56.46% and67.81%,respectively,and the contribution rates of annual precipitation to runoff and sediment discharge are 43.54% and 32.19%,respectively.From 2015 to 2018,the contribution rates of human activities such as land use to runoff and sediment transport were 33.56% and 80.04%,respectively,and the contribution rates of annual precipitation to runoff and sediment transport were 66.44% and 19.96%,respectively. |
