Temporal And Spatial Variation And Driving Factors Of Surface Water In The Yellow River Basin And Typical Regions

Surface water is an important source of water for agriculture,aquaculture,industrial production and terrestrial ecosystems.It affects evaporation and infiltration during water cycle,regulates local climate and maintains ecosystem stability.The ecological protection and highquality development in the Yellow River Basin have been elevated to a national strategy,with water resources as its core element,affect the stability of the ecological environment and regional economic development of the Yellow River Basin.In recent years,under the combined influence of climate change and human activities,the Yellow River basin has been confronted with problems such as water shortage,sediment deposition and channel change.Therefore,it is significant to reveal the spatial and temporal distribution pattern of surface water in the Yellow River Basin,and to investigate the relationship between surface water and climate change and human activities for the rational development,utilization and protection of water resources.Based on Google Earth Engine(GEE)platform,Landsat remote sensing images from 1986 to 2020 were obtained in the Yellow River Basin and typical regions.Surface water was extracted by combining vegetation index and water index.The spatial and temporal distribution pattern of surface water area in the Yellow River Basin,Hetao area and Xiaolangdi junction reservoir area and the area of water-level-fluctuation zone in the wandering reach of the lower Yellow River were revealed by using trend analysis,dynamic attitude analysis,correlation analysis and transfer matrix analysis.The dynamic variation characteristics of surface water in the Yellow River basin and typical regions are clarified,and the impacts of climate change and human activities on the surface water area change in the Yellow River Basin and typical regions are explored.The main conclusions are as follows:(1)The extraction method of surface water in Yellow River basin and typical regions was established.Based on Landsat 5/7/8 remote sensing images,this paper constructed a surface water extraction method using the modified Normalized Difference Water Index(m NDWI),Normalized Difference Vegetation Index(NDVI)and Enhanced Vegetation Index(EVI),and used HAND index to eliminate potential errors of terrain shadows.The overall accuracy of this method was 94.19%.(2)The spatial and temporal variation patterns of surface water in the Yellow River basin and typical regions was revealed.(i)The spatial distribution of surface water in the Yellow River Basin from 1986 to 2020 was uneven,the seasonal and maximum water area are both decreasing,while the permanent water area is increasing.(ii)From 1989 to 2019,the maximum and seasonal surface water areas in hetao area showed a decreasing trend,while the maximum,seasonal and permanent water bodies showed an increasing trend.(iii)From 1999 to 2020,the interannual and annual variation of the maximum water area in Xiaolangdi pivot project reservoir area was significant,and the interannual changes of the maximum,seasonal and permanent water area showed an upward trend.The ratio of minimum surface water area to maximum surface water area in a year is 1:2.16.The new permanent water body in Xiaolangdi pivot project reservoir area is mainly converted from non-water body,and the reduced permanent water body is mainly converted to seasonal water body.(iiii)Interannual variation in the area of the water-level fluctuation in the lower Yellow River from 1986 to 2020 shows a decreasing trend.Before and after operation of Xiaolangdi pivot project,there are significant differences between inter-annual and intra-annual water-level-fluctuation zones.Before operation,the area of inter-annual water-level-fluctuation zone shows a rapid downward trend,and the variation of area of intra-annual water-level-fluctuation zone shows an "interval fluctuation" trend.After the operation,the inter-annual variation of the area of the fallout zone shows a slow decreasing trend,and the intra-annual variation of the area of the fallout zone shows a trend of "rising-stable-decreasing".(3)The driving factors of surface water in Yellow River Basin and typical regions were explored.(i)The maximum water area of the Yellow River Basin is positively correlated with precipitation and land water storage,and negatively correlated with temperature,surface water withdrawals,groundwater withdrawals and surface water area in the previous year.(ii)Variation in surface water area in the Hetao area is mainly influenced by large water bodies,and variation in the number of water bodies is mainly influenced by small water bodies.The area and number of the maximum,seasonal and permanent water bodies in Hetao are positively correlated with precipitation,but negatively correlated with temperature and irrigation area.(iii)The surface water area of xiaolangdi pivot project reservoir area is positively correlated with precipitation and runoff,among which the runoff is the key factor affecting the change of surface water area in the reservoir area.(iiii)The area variation of water-level-fluctuation zone is affected by sediment amount,precipitation,dam and reservoir,among which sediment amount has the most significant effect.