Study On Rainfall-runoff-evapotranspiration And Spatial Distribution On The Loess Plateau

This research was carried out in National Observatory System for the Forest Ecosystem in Ji Country,Shanxi province.There were 11 land use types in the basin.In every typical landuse type,we carry out hydrological observation at slope-scale.Observation include:precipitation,canopy interception,surface runoff,plant transpiration,soil evaporation and so on.Based on this and combination of meteorology,land use and other basic data,comparative analysis of different types of hydrological characteristics of the slope,obtained the spatial distribution of the basin hydrology.The results show that the number of for 6 to 13 times/year,which was accounted for 52.3%～60.4%by the total rainfall throughout the year.The erosive rainfall was the major rainfall which caused soil erosion on study area.The average of annual canopy interception of different land use types was showed as followed:91.46mm in artificial Robinia pseudoacacia,90.73 mm in natural secondary forest,68.96mm in artificial Pinus tabulaeformis forest;the order of canopy interception rate showed as follows: artificial Robinia pseudoacacia(18.70%)＞natural secondary forest(18.55%)＞artificial Pinus tabulaeformis forest(14.10%).There was a good linear relationship between the forest rain and the natural rain.With the increase of natural rain,the forest rain also increased.The range of increase as follows:artificial Robinia pseudoacacia＞natural secondary forest＞artificial Pinus tabulaeformis forest.There were significant differences in runoff coefficient of different land types at slope scale.The runoff coefficient was showed as follows:16.25%in bare land.9.60%in artificial Pinus tabulaeformis forest.6.38%in waste-grassland.1.95%in shrubbery,0.82%in artificial Robinia pseudoacacia forest and 0.72%in natural secondary forest.The average runoff coefficient of the whole basin was 3.89%. The runoff interception rate was showed as follows:95.92%in secondary forest.94.95%in artificial Robinia pseudoacacia forest,88.00%in shrubbery,60.74%in waste-grassland and 40.92%in artificial Pinus tabulaeformis forest.Seasonal variability was observed in the relationship between slope runoff coefficient and rainfall intensity in the same land type.There was exponential correlation between the slope runoff coefficient and the rainfall intensity.Surface runoff was more easier formed in spring and autumn than in summer under the same rainfall intensity.The reduction rate of flood peak discharge w as 86.44%～98.38%in secondary forest.64.21%～99.11%in artificial Robinia pseudoacacia forest, 51.93%～95.61%in shrubbery,14.24%～84.79%in waste-grassland and 17.74%～97.26%in artificial Pinus tabulaeformis forest,respectively.Flood peak discharge showed an exponential correlation with I₃₀or I₁₀,but the relationship between flood peak discharge and I₃₀is superior to that between flood peak discharge and I₁₀.According to runoff coefficient,the research area can be divided into four grades as follows:typeâ… was mainly consist of artificial Robinia pseudoacacia forest,artificial Pinus tabulaeformis forest and artificial mixed forest(artificial Robinia pseudoacacia forest and artificial Oriental arborvitae forest),with their runoff coefficient 0～1.0%;typeâ…¡was related to shrubbery and orchard dominated by apple and pear trees,with their runoff coefficient 1.0%～5.0%;typeâ…¢was involved with artificial Pinus tabulaeformis forest,waste-grassland and farmland,with their soil evaporation 5.0%～10.0%;typeâ…£was related to architectural land and unused land,with their runoff coefficient beyond 10.0%.Daily plant transpiration of different land use types was in the following descending order: 2.60mm/d in natural secondary forest,2.33mm/d in orchard,1.82 mm/d in farmland,1.51mm/d in artificial mixed forest,1.96mm/d in artificial Robinia pseudoacacia forest,1.40mm/d in shrubbery, 1.27mm/d in artificial Pinus tabulaeformis forest,0.75mm/d in waste-grassland,with the average plant transpiration of the whole watershed 1.73mm/d.Daily plant transpiration curves with different land use type had the same tendency of change,which was closed related with solar radiation and showed as single peak type or double peaks type.Solar radiation was the main factor on plant transpiration. According to daily plant transpiration,the research area can be divided into seven grades as follows: typeâ… was mainly consist of architectural land and unused land,with their plant transpiration 0～0.5 mm/d;typeâ…¡was related to waste-grassland,with its plant transpiration 0.5～1.0mm/d;typeâ…¢was involved with artificial Pinus tabulaeformis forest and shrubbery,with their plant transpiration 1.0～1.5mm/d;typeâ…£was involved with artificial Robinia pseudoacacia forest,artificial mixed forest and farmland,with their plant transpiration 1.5～2.0mm/d;typeâ…¤was orchard,with its plant transpiration2.0～2.5mm/d;typeâ…¥was natural secondary forest,with its plant transpiration 2.5～3.0mm/d and typeâ…¦was water area,with its soil evaporation beyond 3.0 mm/d.Daily soil evaporation of land use types was in the following descending order:1.82mm/d in farmland,1.44 mm/d in shrubbery,1.42 mm/d in artificial Robinia pseudoacacia forest,1.15mm/d in orchard,0.89mm/d in artificial in artificial Pinus tabulaeformis forest,0.75mm/d in natural secondary forest,0.69mm/d in waste-grassland,0.53mm/d in artificial mixed forest(artificial Robinia pseudoacacia forest and artificial Oriental arborvitae forest),with the average soil evaporation of the whole watershed 0.95mm/d.Daily soil evaporation curves with different initial soil water content had the same tendency of change,which is closed related with the meteorological factors such as solar radiation,forest temperature,forest humidity and so on.Daily soil evaporation increases with initial soil water content,and they had a liner relationship.According to daily soil evaporation,the research area can be divided into eight grades as follows:typeâ… was mainly consist of residential district,roads,stony area and other unused land,with its soil evaporation 0～0.5 mm/d;typeâ…¡was related to artificial mixed forest,waste-grassland and natural secondary forest of Populus davidiana,Quercus liaotungensis Koidz and Oriental arborvitae,with its soil evaporation 0.5～0.75 mm/d;typeâ…¢was artificial Pinus tabulaeformis forest,with its soil evaporation 0.75～1.0mm/d;typeâ…£was involved with orchard dominated by apple and pear trees,with its soil evaporation 1.0～1.25mm/d;typeâ…¤was involved with artificial Robinia pseudoacacia forest and shrubbery,with its soil evaporation 1.25～1.50mm/d;typeâ…¥no land use type was involved,with its soil evaporation 1.50～1.75mm/d,typeâ…¦was farmland mainly planting Zea mays L,with its soil evaporation 1.75～2.0mm/d,and typeâ…§was water area,with its soil evaporation beyond 2.0 mm/d.