| The karst area of southwest China is one of the three concentrated karst areas in the world,it is the largest karst area and most developed karst areas,where mainly distributed in Yunnan,Guizhou and Guangxi.The bed rock is high permeability and the land surface water resources are lacking,which resulting soil moisture is the dominant restrictive factor for plant growth in this region.Due to its special geological structure,this region characterized by rugged terrain,shallow soil layer and discontinuous soil cover,leading to strong spatial heterogeneity of soil moisture,and the influencing factors of soil moisture change are complex and diverse.However,the spatio-temporal variation of soil moisture and its relationship with influencing factors are still unclear in Yunnan,Guizhou and Guangxi.Therefore,this paper first analyzed the spatio-temporal characteristics of annual and inter-annual changes of soil moisture during 1982-2015 based on linear trend analysis and M-K mutation test.Secondly,based on the method of geographic detector,the influencing factors such as topography,climate,vegetation cover,land use and soil type on the spatial heterogeneity of soil moisture were analyzed,thus the main influencing factors of the spatial heterogeneity of soil water were identified.Finally,based on residual analysis method,the contribution of climate change and human activities to soil moisture change was analyzed,therefore,the main influencing factors of soil moisture time change process were analyzed.The main conclusions of this paper are as follows:(1)During 1982-2015,soil moisture in Yunnan,Guizhou and Guangxi mainly experienced a drying trend,the abrupt change year of soil moisture was 1999.The decreasing trend of soil moisture during 2000-2015 was more obvious than that during 1982-1999.The decreasing trend of soil moisture was more obvious in the karst basin,the karst peak cluster-depression and the karst middle and high mountains.(2)The spatial distribution pattern of soil moisture over the years was high in the east and south,but low in the central and northwest.The maximum soil moisture(0.45 m~3/m~3)distributed in karst trough valley,the minimum soil moisture(0.33m~3/m~3)distributed in karst moderately high mountains.When the altitude was greater than 1441 m and the slope was greater than 25°,the soil moisture decreased significantly with the increase of altitude and slope.The soil moisture content was higher on the north,northwest and northeast aspect,but lower on the other aspect.The soil moisture under different land use cover types shows as:cultivated land>grass land>forest land>unused land.The soil moisture of limestone soil,brown soil and paddy soil was high,while that of brown coniferous forest soil,yellow brown soil and lateritic soil was low.(3)During 1982-2015,the climate in Yunnan,Guizhou and Guangxi showed a warming and drying trend,The variation rate of annual precipitation and the annual average temperature were-22.85 mm/10a and 0.30℃/10a,respectively.The annual precipitation and annual average temperature decrease from southeast and southwest to central and northwest.The precipitation and temperature were high in peak-cluster depression and peak forest plain,but low in karst moderately high mountains.The annual average NDVI in the study area mainly fluctuated and increased,with a variation rate of 0.008/10a.The spatial distribution of annual average NDVI in the study area mainly decreased from southeast and southwest to central and north,and there were significant differences in the annual average NDVI in different geographic units.The high NDVI mainly distributed in non-karst region,peak-cluster depression,peak forest plain,karst trough valley,while the high NDVI mainly distributed in karst moderately high mountains,karst plateau,karst gorge and karst basin.(4)The spatial distribution pattern of soil moisture in Yunnan,Guizhou and Guangxi is mainly affected by precipitation,geographic unit,soil type and elevation.The spatial distribution pattern of surface soil moisture was not affected by a single factor,but by the synergistic interaction of multiple factors.Since 2000,human activities contributed 58.68%and climate change 41.32%to the change of soil moisture in the karst areas of southwest China from 2000 to 2015.The influence of human activities on soil moisture change is greater than that of climate change,which is the main reason for the decrease of soil moisture in Yunnan,Guizhou and Guangxi.(5)The results of this study indicated that the surface soil moisture in Yunnan,Guizhou and Guangxi experienced a decreasing trend during 1982-2015,and the climate showed a warming and drying trend,which was not beneficial to the soil water conservation in this region.In the practice of ecological construction,attention should be paid to the soil moisture conservation in the karst moderately high mountains,the areas with an elevation of greater than 1441 m and the slope greater than 25°,as well as the unused land.Additionally,the correlation between water consumption of forest and soil moisture status,so as to avoid the vegetation restoration reduce on soil moisture,such as controlling suitable forest vegetation density and reasonable forest structure.The research results of this study is not only of great significance to know the regional spatio-temporal dynamics of soil moisture,hydrology model research and soil moisture scale conversion,but also has an important guiding role for the water resource reasonable utilization in agricultural development and ecological construction... |
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