| Watershed runoff is an important part of the hydrological cycle,a fundamental factor in the change of river hydrological situation,and one of the main driving forces of soil erosion.Watershed runoff and sediment yield are generally inf luenced by climate and land use/vegetation underlying surface natural geographic factors,there is spatial heterogeneity,the scale of hydrological cycle is different,the sensitivity of runoff sand yield to climate and land use/vegetation change response There are also differences.Therefore,previous studies on a single watershed are difficult to answer the relationship between runoff and sediment production and the environment.In this paper,the integrated analysis method is used to collect the research results related to runoff and erosion research under land use/vegetation changes on a global scale.The land use/vegetation under different regional/spatial scale differentiation is systematically,comprehensively and objectively discussed.The general law of runoff and sediment production under different changes;studied the runoff,sediment production effect and ecological sensitivity under the change of land use/vegetation under the background of compound watersheds and forest watersheds;analyzed the physical characteristics of different zones,altitudes,and underlying surfaces Characteristics and other spatial heterogeneity,the ecological hydrological effect and ecological hydrological sensitivity of the watershed;the ecological hydrological response threshold value of runoff and sediment production in the watershed was explored;finally,the conclusions of some parts of the world were carried out using long-term observation data of typical watersheds and the Zhang model simulation method Regional verification and resolution.(1)The ecological and hydrological sensitivity under different vegetation types in the composite watershed is forest land(1.16±0.13%)>agricultural land(0.86±0.15%)>shrub grass(0.49±0.06%),indicating that the impact of forest land on runoff The land is large,and in areas with unbalanced water resources,adjusting forest vegetation will signif icantly improve runoff conditions;the sand-sensitive agricultural land under different vegetation types(2.23±0.58%)>shrubland(2.01±0.55%)> forest land(1.51± 0.30%),the agricultural land in the composite watershed has a greater impact on sand production than forest land.In areas with severe erosion,adjusting the regional farmland structure will significantly improve the sand production.(2)There is spatial heterogeneity in the correlation between runoff and vegetation change in forest basins.The southern temperate zone mainly exhibits a negative correlation,the tropical zone mainly exhibits a positive correlation,and the northern temperate zone forest-water relationship is the most controversial.The drought index is generally positively correlated;the runoff effect of vegetation changes in small-scale watersheds has large spatial variability;the effect of vegetation on runoff regulation under extreme rainfall conditions is weak;the effect of shrub vegetation on 750-1000 meters elevation is optimal;sand The response of runoff to vegetation change in soil or sandy soil type areas is signif icantly higher than that of other soil types.The runoff effect of vegetation change in the middle and low altitude regions of the North Temperate Zone decreases with increasing scale,and the ecological and hydrological functions of the vegetation in the water-restricted areas are too large or too small,and the vegetation's inhibitory effect on runoff will increase with rainfall.Large and elevated;in areas with low rainfall and heavy rainfall,the effect of vegetation runoff control is weak.The relationship between forests and water in tropical and energy-restricted areas,small-scale watersheds,and extreme precipitation conditions is prone to controversy,and most of them occur in watersheds dominated by broad-leaved forests or shrub vegetation.(3)The ecological hydrological sensitivity of the pure forest-dominated watershed is greater than that of mixed forests.From a regional perspective,the maximum change in eco-hydrological sensitivity in the southern temperate basin is 3.76 mm/1%,and the maximum is 0.95 in the north temperate zone;the change in eco-hydrological sensitivity is negatively correlated with the drought index,and the eco-hydrological sensitivity is The drought index is positively correlated;the maximum change of ecological hydrological sensitivity at low altitudes of 0-250 m is3.22mm/1%;the change of ecological hydrological sensitivity increases with the increase of precipitation.From the perspective of regional coupling,the eco-hydrological sensitivity of the northern temperate watershed gradually decreases with the increase of rainfall,and the opposite is true in the tropical region.The relationship between the eco-hydrological sensitivity of the southern temperate zone and rainfall is not significant;The watershed scale increases and increases;the transitional and energy-limited climate zone 800-1200 mm precipitation interval has the largest change in eco-hydrological sensitivity;the high-altitude and heavy rainfall area has relatively low eco-hydrological sensitivity,and vice versa.(4)There is an environmental response threshold for global scale runoff and sediment production.When the annual rainfall is less than 500 mm or higher than about 2500 mm,the probability of erosion and sand production in the watershed is very small;when the annual rainfall is about 1500 mm,the annual average sand production in the watershed is the largest;when the agricultural land coverage in the watershed is 30%,the yield The sediment yield is the smallest when the coverage is 80%,and the sediment yield is the largest;the rainfall and runoff thresholds of the water-restricted and energy-restricted areas in the northern temperate zone are 116.2mm and322 mm,respectively;762.5mm and 899.4mm respectively;the runoff in tropical regions increases first and then decreases with the increase of rainfall.The threshold of rainfall runoff in water-restricted areas is 784.5mm.When rainfall reaches 2733.7mm,the annual runoff in the basin is the largest,about It is 1460mm;when the rainfall in the transitional area is 611.4mm,the minimum annual runoff in the basin is 119.4mm.The annual runoff in the northern temperate zone increases first and then decreases with the increase of vegetation coverage.When the coverage reaches 60%,the inhibitory effect on runoff begins to appear.The coverage is between 60% and80%.The runoff is the largest and the coverage is greater than At 80%,the inhibitory effect on runoff is significantly increased;the annual runoff in tropical regions decreases first and then rises with the increase of vegetation coverage.When the coverage is 35%,the minimum annual runoff is about 80 mm.The global watershed runoff and sediment production show obvious scale effects as the watershed area increases.(5)The ecological and hydrological sensitivity of the changes in forest land and agricultural land in Haihe Mountain area are 1.27±0.54 and 0.92±0.43,respectively,which is close to the results of the integrated analysis of the global composite watershed;the rainfall runoff threshold of Haihe Mountain area is 341.74 mm,which is the same as that of the global study area.The research results of temperate water-restricted watersheds have an error of only 6%;the annual average flow in the Haihe Mountain watershed first increases and then decreases with the change of forest vegetation coverage.When the forest coverage is about 62%,the watershed production capacity is the strongest,which is the same as the global The results in the northern temperate zone are basically the same;the scale effect expression of the runoff in the Haihe Mountainous area with the drainage area is y =-34.9ln(x)+335.68,which is consistent with the global runoff scale effect function,and the scale conversion coefficient is similar;it is close to the runoff The scale effect of related environmental factors is the internal driving force of runoff scale effect.Meteorological factors are the main direct factors affecting runoff coefficient.Other factors mostly indirectly affect the change of runoff coefficient through climate feedback.Forest land only affects runoff in small-scale watersheds.Coefficient,the increase in agricultural land has the greatest negative effect on runoff coefficient in the mesoscale watershed,with a contribution rate of up to-31%. |
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