The Status And Scale Effect Of The Yanhe River Watershed Soil Monisture

Yanhe River watershed is a typical representative of regional scale in hilly-gully region of Loessplateau.Study on the temporal and spatial distribution of the Yanhe River watershed soil moisture, theimpact of environmental factors on the distribution of soil moisture, and information change under theassumption of various environmental factors from watershed scale to regional scale,which can providetechnical guidance for soil erosion control, ecological reconstruction and sustainable development ofenvironmental systems of regional-scale. In this study, on the basis of the previous researches,whichcontainYanhe River watershed evaporation, precipitation, temperature and terrain factor interpolation,theauthor made a systematic study on Yanhe River watershed soil moisture and the scale effect of the differentscales of soil moisture. The main conclusions are as follows:(1)Generally speaking, through the Yanhe watershed soil moisture descriptive statistice, soil moisturein0-20cm and20-40cm had larger differences with other layers,especially before the rainy season.Soilmoisture changed smoothly and stably, and soil moisture was also larger different in the same soil layer ofdifferent locations, especially in the rainy season the coefficient of variation changed more complex.Thehysteresis effect of soil water infiltration was not obvious in0-80cm layer, soil moisture in the rainy seasonwas significantly greater than both before the rainy season and after the rainy season;80-200cm layershowed significant hysteresis effect.（2） The researches and analysis were carried out to study vertical the profiles of soil moistureclassification using sequential clustering method. The profiles of soil moisture was classified to5land-usetypes such as argricutural land, woodland, shrub land, orchard and grassland land use types on loess hillyregion. When K=5, there is an optimal ordered partition. According to various land use types, overall, thevertical soil moisture profile in this area can be divided into4types: weak moisture utilizing layer, rootconcentration layer, strong water consumption layer, and moisture regulating layer, which was easy to findthe main fact of soil water in different scales.（3）Through mathematical statistics on soil moisture and environmental factors of the Yanhe Riverwatershed,the results showed that:For the study area,no aspect of soil moisture content was highest,soilmoisture in north slope and the north by west were higher than in the south slope and the south by east.Damtableland soil moisture was highest,due to land-use types of Hilly top were often terraces, so its soil moisture content was after the Dam tableland;consistent with the study on aspect and slope position,agricultural land soil moisture was highese, while shrub woodland was lowest among different land-usetypes. Meteorological factors (precipitation, temperature, evaporation) had significantly correlated with soilwater content, and effects of precipitation and temperature were particularly prominent. In the study areas,slope and elevation influenced on soil moisture were not as good as meteorological factors.（4）Studies of land, slope, watershed and reginal scales had shown that:The slope and slope positionwere the master factors in the plot scale. Slope position and land-use types were the master factors in theslope scale, slope, land-use types and elevation were the master factors in the small watershed scale, andevapotranspiration, precipitation, temperature and types of land-use were the master factors in the regionalscale, all of which influenced on soil moisture. Small-scale soil moisture was closely related withmicrotopography. With the sacle increasing, the amount of information, which assumed by aspect, slopeposition, slope and other topography, gradually moved to evapotranspiration, precipitation, temperature andother meteorological factors. The amount of information, which assumed by land-use types, changedrelatively stable.According to screening the main control factors influenced on soil moisture, simulated on soilmoisture curved surface of the Yanhe River watershed and then found that the calculation of thin smoothspline function method was more complex and accurate,no longer showed a patchy mosaic distribution ofby sampling points as the center, but showed the transitional changes with the topography,so the resultsfrom the method were more in line with the actual situation of soil moisture changes.