Remote sensing analysis on gully morphology and spatial distribution in rolling hilly region and mountainous and hilly region of Northeast China

Gully erosion is the frequent and main form of soil erosion in the black soil region of the northeastern China, and has posed a threat to food security. There are 295 663 gullies present in this region according to calculations of the results of the first-ever nationwide water resources survey, and 88.9% of the gullies were active. Besides, morphological characteristics of gully are important for both representing environmental factors of the development of the gully and for understanding the mechanism of the gully erosion. However, information on characterizing morphological parameters of gully (e.g. gully length, gully width, gully area) using the remote sensing images with resolution would be higher than 0.61 m is not available. The aim of this paper was to explore the gully morphological characteristics, based on high-resolution remote sensing images (e.g. QuickBird (0.61 m)，GeoEye-1 (0.5 m)，Worldview 2 (0.5 m)), and to give an analysis on spatial distribution properties. In this research, 113 and 74 gullies were selected in the rolling hilly region and mountainous and hilly region of northeast China, respectively, and the values of morphological parameters extracted from the high-resolution remote sensing images, and then the gully length (L, m), gully width (W, m), gully perimeter (P, m), gully area (A, m2), and shape index (SI) were extracted by manual visual interpretation. The digital elevation model (ASTGTM2, 30 m) data were combined with data on gullies occurring on farmland with different slopes and aspects to analyze the distribution of these features, and GIS spatial analysis and geostatistical analysis methods were employed in this study. The results showed that the average values of the gully length, gully width, gully perimeter and gully area were 412.8 m, 14.7 m, 917.4 m, 7 309.8 m2 in the rolling hilly region. Respectively, those of parameters were 309.9 m,7.8 m, 683.1 m, and 2934.1 m2 in the mountainous and hilly region, and there was no significant (P>0.05) difference between the two regions (one-way ANOVA). The average value of the ratio between gully width and length in the mountainous and hilly region was greater than the rolling hilly region, indicating the gullies were much longer and thinner, and, subsequently, the SI in the mountainous and hilly region was much greater, which indicated the position of gully boundary was more complex in this region. Morphological parameters of gully initially increased with increasing slope up to some threshold value, then decreased as the slope increased further. Within the range of 3 - 6°, morphological parameters of gully were to reach the highest. The smaller the gradient of the gully was, the more complex the gully boundary was. In this study，morphological parameters of gully in southwest and southeast aspect were much larger than the other aspect, indicating that the intensive gully erosion in sunny slope or semi-sunny slope. The results can not only reveal the law of morphological parameter differentiation of gully erosion and help predict their spatial development, but also determine the erosive gully prone area and control gully erosion.