Karst regions are typically geologically constrained and ecologically fragile. Karst landscapes can be greatly affected by external factors such as environmental change. Southwestern China has one of the largest karst regions in the world which extends over about 540000 km² and is home to more than 220 million people. Desertification of the karst environment in this region has expanded at an increasing rate over the last few decades. Water and soil loss processes, and in particular the spatial distribution patterns of water and soil loss, in the karst regions of southwest China are particularly unique. This is due to the solubility of the carbonate rocks that results in a low rate of soil formation, a low-tolerance for soil loss, high topographic relief and the destruction of vegetation. In this study, rainfall erosion, topographic relief, soil types, vegetation types, and soil loss tolerance were selected as indicators used to assess water and soil loss sensitivity. Using GIS techniques, we evaluated the water and soil loss sensitivity of each individual indicator then integrated the results to examine the differences in the spatial distribution of water and soil loss in southwestern China. The results show that rainfall erosion, topographic relief, soil types, and soil loss tolerance are highly sensitive to water and soil loss in karst regions, whereas vegetation cover is not as sensitive. Water and soil loss sensitivity in the karst regions of southwest China is generally high, with more than 82.76% of the karst regions classified as being at least moderately affected and only 6.4% of the area classified as insensitive. The spatial distribution analysis indicated that karst regions with moderate of higher deteriorative water and soil loss sensitivity are mainly distributed in northeastern and southeastern Chongqing, southwestern Hubei, northwestern Hunan, most of Guizhou, northeastern Yunnan, and the peak-cluster depression of Guangxi. In addition, as the content of insoluble acidic material in the soils increased, the areas with extreme or high sensitivity to water and soil loss declined, but those with moderate sensitivity to water and soil loss increased.
In addition to usual factors such as precipitation, terrain conditions, soil cover, and vegetation, the distribution of ground water and soil loss in karst regions is significantly related to soil loss tolerance. As a result, soil loss tolerance must be considered as an important indicator of water and soil loss in karst regions. However, when the water and soil loss reaches extreme levels, exposed bedrock can become widely distributed. In this situation, there is no water or soil to lose and karst rock desertification occurs. Our results suggest that increases in the extent of karst rock desertification can be taken as a primary indicator of water and soil loss in this region. Therefore, occurrences and changes in karst rock desertification should be taken further into consideration to enhance regional prevention and remediation plans directed at water and soil loss and karst rock desertification. Our study provides useful references for the prevention and control of water and soil loss and the ecological restoration and reconstruction of degraded karst system in southwestern China.