Human Causes of Aeolian Desertification in Northern China

Aeolian desertification has rapidly developed in the past 50 years in Northern China,covered an area of 0.386 million km2 by 2000,affected nearly 170 million population,and caused the direct and indirect economic loss of about $6.75(U.S.dollar) billion per year.Here we present several lines of evidence to demonstrate that human activities guided by policy shifts have been a major force to drive aeolian desertification via changes in land-use patterns and intensity.It is suggested that the desertification can be curbed or even reversed by adopting prevention and control measures with ecologically sound land-use practices in China.

Changes in wind activity from 1957 to 2011 and their possible influence on aeolian desertification in northern China

Wind activity is proved to have significant impacts on aeolian desertification. Clarifying the fluctuations and change trend of wind velocity is important for understanding their influence on aeolian desertification. In this study, we used a dataset of wind velocities collected from 93 meteorological stations across northern China from 1957 to 2011 to analyze the changes in wind activity during this period. We tested the monotonic and step（abrupt） trends for annual and seasonal data of mean wind velocity by using Mann-Kendall and Mann-Whitney tests, respectively. The results indicated that the annual mean wind velocity decreased by 0.83 m/s from 1957 to 2011. The decreasing trends were also significant（P〈0.01） for each season. The magnitude of the decrease was smallest in the east of northern China and largest in the west of northern China, and the most remarkable decrease occurred in the northwest of northern China. Abrupt decreases in annual and seasonal mean wind velocities occurred in the mid-1980 s, which was consistent with the changes in aeolian desertification since the mid-1980 s in northern China. As revealed by our study, although both modern aeolian desertification and ecosystem rehabilitation are affected by human activities to some extent, they are also likely to be strongly controlled by climate change, especially by wind activity.

Mapping the dynamic degree of aeolian desertification in the Shiyang River Basin from 1975 to 2010

The Shiyang River Basin is an area of China that is severly affected by aeolian desertification.Thus,we established an aeolian desertified land classification system for visual interpretation,which classified the Aeolian Desertified Land(ADL)into Slight(SL),Moderate(M),Severe(S)and Extremely Severe(ES)according to the severity.Imagery of Landsat series(acquired in 1975,1990,2000 and 2010)were employed to monitor the status,trend and spatial pattern of aeolian desertification,especially to map the overall spatial pattern of ADL dynamics by proposing a new Dynamic Index(DI)in the Shiyang River Basin from 1975 to 2010.The results show a generally decreasing trend from 1975 to 2010.However,the ES ADL kept increasing throughout the whole study period.Moreover,the area of ADLs with different severity increased with increasing severity,this S and ES ADLs dominated characteristics of aeolian desertification was contrary to those sandy lands in eastern China where was dominated by SL and M ADLs.Among the three sub-periods of 1975−1990,1990−2000 and 2000−2010,the first two were the restoration stage,while the last one was the expansion stage of aeolian desertification.Moreover,all these new ADLs occurred in Minqin County during 2000−2010,indicating a detrimental increase of aeolian desertification in Minqin,and the concentration of ADLs toward the lower reaches of the Shiyang River Basin.The DI works well to identify areas with desertification changes no matter the sub-periods.Moreover,DI results disclosed a stable status of aeolian desertification,and the DI decreased with increasing ADL severity.These results indicate that it will be difficult to control the expansion of aeolian desertification in Minqin County over an extended period of time.Thus,we suggest effective and long-lasting aeolian desertification control programs in the Shiyang River Basin,especially in Minqin,and SL and MADLs should have priority in facilitating a quick reversal of aeolian desertification.

Deserts and Aeolian Desertification in China: Book review and some thoughts

Desertification is a global phenomenon that affects about two billion people. It occurs in arid zones where the annual precipitation is below 400 mm, partic- ularly in the marginal areas of the world＇s largest deserts. It is a result of water and wind erosion, over- grazing, global warm-ing, improper soil cultivation, and increased pressure ot population growth, and it causes degradation of soil and natural and agricultural vegetation. The direct result is less food for people and livestock, which influences pop- ulation and animal husbandry fluctuations. Despite ef- forts to combat and reduce desertification, the affected areas are annually increasing.

Aeolian desertification and its control in Northern China

Aeolian desertification is a kind of land degradation through wind erosion resulted from the excessive human activities in arid,semiarid and part of sub-humid regions in Northern China.To compare the results of remote sensing data in the late 1950s,1975,1987,2000 and 2010,we can summarize that the expansion of aeolian desertified land in Northern China has been accelerated for 5 decades,as its annual expanded rate was 1,560 km^(2) during the late 1950s and 1975,2,100 km^(2) between 1975 and 1988,3,600 km^(2) from 1988 to 2000,and-1,375 km^(2) from 2000 to 2010.The desertified land kept expanding before 2000 and began to get rehabilitated since 2000.The impact of human activity on the aeolian desertification process is much more active than that from natural process which mainly incarnates on land use change(from rangeland to farmland)and increased land use intensity(over-cultivation,over-grassing,and over-fuelwood collection).The natural vegetation cover destroyed by the human activities has accelerated the development of aeolian desertification.China has made great progresses in understanding and combating aeolian desertification through decades of effort and there were many projects carried out for the prevention and control purpose.The National Project of Grain for Green Program is the most important one with 1060 counties of 22 provinces involved.The objective is to withdraw 3.67 million ha of dry land farming and degraded steppe,and 5.13 million ha of aeolian desertified land suited to reforestation and re-vegetation will be rehabilitated.There are about 8 million ha of lands suffering from aeolian desertification will be brought under control in the next ten years and 26.67 million ha of windbreaks will be planted.The total investment from the central government is estimated to be 75 billion RMB(11 billion USD).

Land surface roughness impacted by typical vegetation restoration projects on aeolian sandy lands in the Yarlung Zangbo River valley,southern Tibetan plateau

Aeolian sandy lands are widespread and desertification is recognized as one of the main environmental issues in the Yarlung Zangbo River valley,southern Tibetan plateau.The surface microtopographic var-iations induced by the near soil surface characteristics of plant communities are important compositions of land surface roughness,which likely influence wind erosion.This study was conducted to quantify the effects of typical vegetation restoration on land surface roughness on the aeolian sandy lands,and to identify the main influencing factors of land surface roughness in the Yarlung Zangbo River valley.Two bare sandy lands(as controls)and eight vegetated sandy lands with different restoration communities and ages were selected,and land surface roughness(LSR),as represented by surface microtopographic variations in this study,was measured by photogrammetric surveys.The results showed that LSR significantly increased by 7.9-16.8 times after vegetation restoration on the aeolian sandy lands,and varied among different restoration communities and ages.The mostly restored communities of Sophora moorcroftiana and Populus L.had greater LSR as compared to Artemisia wellbyi and Hedysarum scoparium.With succession from 6 to over 30 years,LSR gradually increased in the Sophora moorcroftiana restored sandy lands,but decreased in the Populus L restored sandy lands.The variations of LSR were mainly attributed to the differences in near soil surface characteristics of vegetation(plant stem diameter and coverage,and plant residue density)and biological soil crusts(coverage and thickness).Mixed plantation of Populus L and Sophora moorcroftiana was considered as the best restoration communities because of their effectiveness in increasing land surface roughness on the aeolian sandy lands in the Yarlung Zangbo River valley.The results would facilitate the understanding of the benefits of vegetation restoration in controlling wind erosion on the aeolian sandy lands.