| In order to analyze soil moisture condition and distribution characteristics of different vegetation zone and small watershed in Yan river basin, this study took different vegetation zone and its small watershed in loess hilly-gully region as object. The soil moisture vertical distribution characteristics and variation coefficient before and after rain, spatial distribution and variation law of soil moisture, change rule and characteristics of terrain factors under different resolution DEM between small watershed and Yan river basin have been researched. According to the terrain factors under different resolution DEM and its soil moisture condition and distribution characteristics, terrain factors impacting on soil moisture and scale have been described. The main conclusions are as follows:(1) Soil moisture content of different soil layer had significant differences in Yan river basin, and increased with the increasing of soil depth, but CV was opposite. Its soil moisture after the rainy season was significantly higher than before the rainy season. And soil moisture was proportional to depth after rainy season, increased at first then decreased with soil depth before rainy season. Moreover, soil moisture content of different environmental conditions showed a decreasing trends from south to north for the whole Yan river basin. Same layer soil moisture varied from different sites, CV was less than before the rainy season, surface soil moisture had a big difference before the rainy season, deep soil moisture had a big difference after rainy season.(2) There was a significant difference on soil moisture in different vegetation zone, its order was forest belt, forest grassland, grassland. According to the analyze to soil moisture of different vegetation, soil moisture increased with increasing of soil depth between 0cm and 200 cm, and there was a significant difference on average soil moisture in small watershed, its order was forest, forest grassland, grassland, reflected a decreasing tendency from south to north. Soil moisture in every small watershed increased along with soil depth before rainy season. After rainy season, rainfall infiltration resulted in soil moisture gap decreasing between surface and deep soil. Moreover, CV of small watershed soil moisture in every vegetation zone before rainy season were much bigger than after rainy season.(3) There was a good diminishing linear relation between average slope and resolution as the continuous falling of resolution. Their slop showed an attenuation, and mainly took place in steep slop, and value of slop increased in steep slop, decreased in gentle slop, where got close to the middle, without obvious fluctuation, these made all terrain blurred gradually. Among three small vegetation watersheds, topography is highest in Zhou Jiashan watershed, its each terrain was small discrete because of gentle slop. Same tendency in Mao Baoze, but in Chen Jiagua, which had minimum elevation in most steep slops and more complex terrain. Moreover, three small watersheds showed increasing at gentle slop, cutting at steep slop, concentrating to middle. Slope did not change significantly to overall and ground was decreased, continue to reduce to zero after 40 m DEM. Compared the characteristic of terrain between small watershed and Yan river basin, terrain factor had less change in Yan river basin, more change in small watershed under decreasing of resolution ratio.(4)Slop and soil moisture had a significantly negative relation at 0.05 level, and same to exposure and soil moisture in Yan river basin. There was a significant correlation between elevation and soil moisture at 0.01 level. But having a significant negative correlation between each terrain and soil moisture at Chen Jiagua basin, gradient and elevation got negative correlation with soil moisture at 0.01, same with exposure at 0.05. The order of significance was gradient, elevation, exposure. Gradient had the same correlation with soil moisture at 0.01, but a weak negative correlation with exposure, opposite correlation between elevation and soil moisture. There was no obvious effect on terrain and soil moisture as changing of resolution at regional scale, and without obvious fluctuation among gradient, exposure, elevation and soil moisture even increasing of DEM. However, it was opposite in small basin, the correlation between terrain and soil moisture had an obvious fluctuation with decreasing of resolution, the changing order was Mao Baoze, Zhou Jiashan, Che Jiagua. |
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