Studying On The Soil Erosion Risk By Water In China

With growing global population and increased high demand for food and for living standards,soil erosion rates are increasing,bringing a series of environmental problems,and seriously threatening sustainable development of resources,environment and social economy.Those have gradually attracted the attention of governments and soil erosion has been become one of the most important research topics in soil science,agricultural science and environmental science.China is one of the countries with the most serious soil erosion around the world and its soil erosion is featured by complex formed reasons,widely distribution,huge loss,severe erosion intensity and severe hazard.Therefore,the task of soil erosion and water sedimentation becomes more and more arduous and the demand of governments for soil erosion research is more urgent today than ever before.Based on soil science,geomorphology,remote sensing and GIS techniques,spatial statistics,information theory and risk viewing-control analysis of Pansystems technology,we determined the study area under a framework of first class of soil erosion by water and the soil-water conservation zones,and collected weather station data,multi-sensor and multi-temporal remote sensing data,China soil at 1:1000000 scale,and ecological environment background data for extracting and calculating factors affecting soil erosion by water,such as soil erodibility,rainfall erosivity,relief amplitude,vegetation coverage,and land use structure.We analyzed their spatial-temporal changes.The risk assessment model of soil erosion by water was built with determining the weight of influencing factors in each soil-water conservation zone and combining the erosion risk factor.We systemically studied on regional soil susceptibility,erosion sensitivity,potential erosion risk and natural erosion risk from the point of view on soil and water conservation,and analyzed variations of erosion risk exploring their driving factors.Combined with China land use/cover at 1:100000 scale and China soil erosion intensity at 1:100000 scale,we analyzed responses of erosion risk variation to land-use changes and the relationship between soil erosion risk index and soil erosion intensity.(1)There is a severe soil erosion environment in China,where has 60% of lands with weaker soil susceptibility(2 and below level)and other 40% with stronger soil susceptibility(3 and up level).The lands with highest soil susceptibility are mainly distributed in the west and middle part of North wind-sand area(NWSA),the northwest Loess Plateau(NLP),the southeastern and northern Tibetan Plateau(TP),the west of Southwest China(SC),the north of Northern rocky mountain area(NRMA),and the south of the black soil region of Northeast China(BSRNC),while the lands in Northeast Plain area(NPA),Sanjiang Plain area(SPA)and North China Plain area(NCPA)are with weakest soil susceptibility.(2)The soil erosion sensitivity was high in the West,such as the NLP with the higher erosion sensitivity,the rocky mountain area of Northern China with above moderate erosion sensitivity,north wind-sand area and TP with high and very high sensitivity,and low in the East,such as red soil region of South China,purple soil region of Southwest China(PSRSC),the karst area of Southwest China(KASC).During 2000 to 2010,the soil erosion sensitivity in the most of areas decreased,and the most significantly decrease is happened in NLP.The main reason of this decrease is that their vegetation coverage ratio obviously increased from 2000 to 2010.However,there were some places with increased erosion sensitivity due to their increased annual variation coefficient of vegetation coverage.(3)Potential erosion risk,which is used to describe the inherent erosive feature of soil,in NLP area is the highest,and in NPA and North China is the lowest.During 2000 to 2010,the variation of potential erosion risk index of study area was non-significant,which means their inherent erosive characteristics of each soil and water conservation zones are relatively stable.(4)Under the joint action of five main factors of soil erosion by water,most of erosion risk indices in each soil-water conservation zone were larger than their potential erosion risk index,which means anthropic activities aggravated the possibility of soil erosion.In the entire study area,the erosion risk of NLP,Southwest mountain area,the north of NRMA and southern TP is relatively the highest.Oppositely,that of NPA and NCPA is relatively the lowest.During 2000-2010,the average erosion risk index of BSRNC,NRMA,red soil region of South China(RSRSC)and(PSRSC)increased slightly,and others decreased.The average erosion risk index of NLP decreased significantly from 2000 to 2010.(5)The variations of erosion risk are significantly correlation with the changes of annual rainfall erosivity,of instantaneous vegetation coverage and of land-use structure index in entire study area during 2000 to 2010.The variation of land-use structure index is the first driving factor among these three factors,and the change of annual rainfall erosivity is the second one.The areas of soil erosion by water with high erosion risk,such as NLP,PSRSC,KASC,TP,the south of Da Hinggan Mountains,and the north of Yanshan Mountains,are high susceptibility mainly limited by their own physical and chemical soil characteristics and terrain environment,combined large annual rainfall erosivity and unreasonable land use types.During 2000 to 2010,those areas of soil erosion by water with increasing erosion risk were mainly affected by changes of single factor or multiple factors from annual rainfall erosivity increased,instantaneous vegetation coverage decreased,and land-use structure index increased.Similarly,those areas of soil erosion by water with decreasing erosion risk were mainly affected by changes of single factor or multiple factors from annual rainfall erosivity decreased,instantaneous vegetation coverage increased,and land-use structure index decreased.(6)The spatial pattern of erosion risk by water was similar to the erosion intensity by water in China,such as the largest area percentage happened in low erosion risk areas and the smallest happened in high erosion risk areas.Both of the area percentage of low erosion risk soil and that of high erosion risk soil obviously increased from 2000 to 2010.There were obvious response characteristics between the erosion risk by water and the erosion intensity by water.The lands with low erosion intensity by water were also with low erosion risk by water and the lands with high erosion intensity by water were also with high erosion risk by water.The area percentages of middle erosion risk and down in most of erosion intensity types obviously increased from 2000 to 2010,and the area percentages of extremely high erosion risk in extreme erosion intensity and severity erosion obviously decreased during this period,which means the erosion risk by water of study area generally trend to become better.The Northwest Loess Plateau is a region with high erosion risk and high erosion intensity,while its area percentage of high erosion risk level significantly decreased from 2000 to 2010.(7)For farmlands,woodlands,grasslands and unused lands these are four main erosion land types,their area percentages of moderate and below erosion risk were all largest,and of extreme high erosion risk were smallest.Relatively,the area percentages of higher erosion risk in grassland area and in unused land area were obviously larger than those in farmland area and in woodland area.During 2000-2010,except woodland areas,the area percentage of low erosion risk trend to increase and that of high and higher erosion risk trend to decrease.However,the area percentages of extreme high erosion risk in farmland area,woodland area and grassland area obviously increased while those in unused land area decreased slightly from 2000 to 2010.In general,land-use structure trends to reasonable,which is useful to soil conservation and protect.