| Yanhe watershed is a typical experimental Soil and Water Conservation District. This paper researched the land use/cover change before and after "Grain for Green Project" in Yanhe watershed, established the relationship between natural environmental conditions, human-socio-economic development and history development, assessed the impact on watershed landscape pattern to ecological important processes.It is important scientific value and practical significance to research watershed landscape pattern and hydrological processes.Using remote sensing and GIS(Geographic Information System) technology and combining with field research and mathematical statistical methods, firstly this paper researched land use/cover change(LUCC) status in Yanhe watershed before and after "Grain for Green Project", then predicted the land use trend by CA-Markov model; analyzed, simulated and predicted ecological hydrological processes in Yanhe watershed based on SWAT model.On this basis, this paper tried to define the landscape unit which included terrain, soil and land use/cover change (LUCC) information and described quantitatively land use/cover change (LUCC) on eco-hydrological processes by landscape indices method, considering particularly those soil erosion influences caused by the change of landscape pattern with the complicated terrain and soil type status in Yanhe watershed, and constructed a comprehensive landscape index which closely related to soil erosion and reflected the coupling relationship between regional landscape pattern change and soil erosion.The main results are as follows:(1) Land-use changes in Yanhe watershed:cultivated land is shrinking, while ecological land is growing. From1990to2010, it shows that pasture, shrubs and forest were growing but cultivated land shrinking. Pasture was the biggest proportion of other types, belonging to the advantages landscape in Yanhe watershed. According to CA-Markov model, the total area of pasture, shrubs and forest will reach66.63%in2020, cultivated land accounting for14.53%, pasture reducing10.59%, garden increasing105.35%, construction land growing89.68%. These changes are consistent with economic and social trends in Yanhe watershed.(2) Hydrological processes in Yanhe watershed:precipitation, runoff and sediment load have regularly temporal variation. Based on historical documents,"droughts and floods time sequence diagram in Yanhe watershed" was generated, which found the historical droughts and floods occurred alternately, and droughts had a great harm. The time series variation of precipitation, runoff and sediment load for recent60years was similar, and had significant correlation. But the correlation was weak between precipitation and sediment discharge, and variation coefficient of precipitation, runoff and sediment transport increased gradually. With analysis on IDW interpolation points chart of6h rainfall, the spatial variation of runoff and rainfall intensity was similar, and presented in descending order from the middle to the east and west sides. However, sediment yield spatial characteristics, being clearly different from spatial distribution of rainfall intensity and runoff distribution, presented the decreasing trend from south to north and from east to west.(3) Construction and application of distributed hydrological SWAT model in Yanhe watershed:with simulated land use/cover change on hydrological effects using SWAT model, it is obtained that the growth of forest, shrub and grassland helps runoff to increase in Yanhe River, and the sediment amount will greatly reduce.(4) This paper attempts to study landscape pattern using hydrological response unit (HRU) as the basic unit:it constituted the spatial heterogeneity of hydrological response unit (HRU) by several factors such as land-use type, soil type, terrain, etc. It attempted to research the space pattern feature of hydrological response unit (HRU) with landscape index method. At the landscape level, it selected seven landscape indices involving DCAD, GYRATESD, COHESION, SHEI, TCA, PAFRAC, IJI, etc., with principal component factor analysis. And based on the analysis on landscape-scale both range and particle size, it determined80m as the appropriate granularity. Coupled analysis on the relationship of landscape indices and annual runoff as well as annual sediment yield in every sub-basin, the correlation coefficient of seven selected landscape indices and runoff is very small, no passing all significant tests. But the correlation between sediment yield and the indices except for TCA and IJI is significant, and the absolute value of the correlation coefficient is between0.3and0.5.(5) Trying to build Slope-HRU landscape index:the coupling relationship between Slope-HRU landscape indices and annual sediment yield in every sub-basin is very clear, and correlation coefficient is-0.6, which is significantly negatively correlated. According to "the source-sink" theory of soil erosion, Slope-HRU landscape index was built, and reflected the relationship between landscape pattern and soil erosion processes to a certain extent. By analysis on the R-value space distribution of the Slope-HRU landscape indices in41sub-basins, the results show that:on the sub-basin scale, Slope-HRU landscape indices and annual sediment have obvious regional differential regularity. And the R-value spatial variation of Slope-HRU landscape indices and the spatial variation of annual sediment amount are on contrary, which is the R-value increasing from southeast to northwest with annual sediment yield decreasing from southeast to northwest.(6) Innovation points:①Hydrological response unit (HRU) was as the basic landscape unit for the first time,constituted by several factors such as land-use type, soil type, terrain, etc.The feature of hydrological response units’ space pattern was researched with landscape index method.②According to "the source-sink" theory of soil erosion, Slope-HRU landscape index was built, which better reflected the relationship between landscape pattern and soil erosion processes. |
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