Assessment And Monitoring Of Land Degradation Using NPP And Vegetation Rain Use Efficency

Land degradation refers to the land productive capacity or the land use and potentialenvironmental regulation continue to decline or even comletely loss under the influence of avariety of natural ecosystems and human activities. Desertification is defined as the landdegradation in arid and semi-arid and dry-sub-humid areas resulting from various factors,including climatic variations and human activities. Desertification is a disaster directlythreatening human survival of the natural environment. The serious consequences is decreasedor loss of the land biological or economic productivity and diversity. Desertification isessentially land degradation. The land degradation which relates to the social economy andnatural sciences is one of the most serious environmental and socio-economic issues in theworld. Land degradation has become increasingly serious and ecological environmental qualitydecreases significantly in China affected by climate change and unreasonable human activities,which seriously affect China’s international image and pose a serious threat to the sustainabledevelopment of the political, economic, cuitural. The maintenance of the ecological safety hasbecome a fundamental guarantee for the sustainable development of economy and society inChina. Monitoring and assessment of land degradation is the core content of desertificationresearch. With the development of remote sensing technology, remote sensing information hasbecome the important sources for land degradation assessment, while provided the technologyand accuracy guarantee for monitoring and assessment of land degradation reseach. Highprecision and quantitative desertification information extraction based on remote sensingtechnology, which is critical to achieving the quantitative assessment and monitoring of landdegradation.On the basis of summarizing the new research achievements and questions at home andabroad for land degradation, this paper tried to assess the land productivity based on vegetationrain use efficency (RUE) and to monitor the vegetation degradation by annual variation ofvegetation net primary productivity (NPP) for long time series, taking the long time series MODIS data as the main data source. Combining with the high spatial resolutionclimatological data, this paper assessed and monitored the land degradation comprehensivelyusing remote sensing technology in the Beijing-Tianjin dust and sandstorm source region forrecent10years, and analyzed the contribution of human activity and climate change to regionalland degradation quantitatively, in order to improve the land degradation assessment andmonitoring technology based on remote sensing at different scale and to provide the basis forbenefit evaluation of the project in the Beijing-Tianjin dust and sandstorm source region andfor the reasonal layout of the future management.The main research contents are as follows:(1) This paper put forward a new comprehensive method for land degradation assessmentbased on RUE and NPP. The land productivity was assessed quantitatively based on relativeaverage RUE（rRUE_me）and extreme maximum RUE（rRUE_ex）, and the land degradationassessment and monitoring were conducted with remote sensing technology by analyzing thevegetation degradation trend based on the long time series NPP variation. Compared with theother methods, this method can reflect the land degradation more objectively and be benefit toassess and monitor the land degradation quantitatively with remote sensing at a larger range.(2) Based on the meteorological data, the annual precipitation, annual average temperatureand moisture index trends during1981-2010were analyzed using a variety of mathematicalstatistics methods in the Beijing-Tianjin dust and sandstorm source region. The results werethat the annual average temperature showed a significant increasing trend, and the precipitationand moisture index exhibited a downward trend in the past30years in the Beijing-Tianjin dustand sandstorm source region. However the downward trend was not significant. In the last30years, there was a significant increase trend in93.12%of the study area for the averagetemperature based on Mann-Kendall test. And for the precipitation and moisture index, therewas a decreasing trend respectively in69.77%and84.93%of the study area. While thesignificant downward trends at0.1confidence level only accounted for18.76%and28.02%inthe Beijing-Tianjin dust and sandstorm source region. (3) The NPP for long time series in the study region was calculated based on the improvedCASA model using monthly MODIS NDVI data for2001-2010, and the RUE data wasobtained, combining with annual precipitation. It can be seen that the NPP and RUE exhibiteda downward trend and the vegetation activity was being degraded in the Beijing-Tianjin dustand sandstorm source region during2001-2010, but the decreasing trends were not significant.There was a downward trend of the NPP in64.24%of the study area using the correlationanalysis method, while only14.74%of the study area was significant at0.1confidence level.The spatial distributions of trends in NPP and RUE were very different in the Beijing-Tianjindust and sandstorm source region. For the NPP, the significantly decreased areas were mainlylocated in the northeastern part of the study area, these significant decreasing regions weremainly a southwest to northeast band within the area, however the spatial distributions of thesignificant downward trends for RUE were scattered.(4) The land productivity was assessed at the pixel level based on the rRUE_me andrRUE_ex. The rRUE_me can reflect the medial state of land productivity for10years, whilethe rRUE_ex can reflect the jamproof restore elasticity of different ecosystems. The resultsshowed that the lands with the lowest and lower productivity accounted for2.45%and5.44%of the total area of Beijing-Tianjin dust and sandstorm source region, which mainly located inthe western arid regions include desert grassland, the central of Otindag sandy land, andNorthern Shanxi’s mountains. While the land with good productivity accounted for92.1%ofthe whole study area.(5) By analyzing the correlation between NPP and time series, the results showed that thevegetation about67.4thousands km~2had degradated in recent10years under the influence ofclimate change and human activities, it took up about14.74%of the whole study area.Meanwhile, the recovered area of vegetation was18.3thousands km~2, which accounted for3.99%of the total area. The degradated vegetation region mainly distributed in the east ofXilingol grassland, located in the northeast of the Beijing-Tianjin dust and sandstorm sourceregion, while the recovered region mainly located in the south of the study area, such as thehilly and mountainous area in the north of Shanxi and Hebei province. (6) By analyzing the results of land productivity assessment and vegetation degradationmonitoring, the comprehensive method for land degradation assessment was put forward, and ithad been applied to assess the land degradation in the study area for recent10years. As theresults showed that the area of degradated lands in the Beijing-Tianjin dust and sandstormsource region was91thousands km~2, and it took up19.88%of the whole area, among whichthe degradated land at severe degree accounted for2.45%and the moderate degree took up5.44%, they were mainly distributed in the western region, such as Inner Mongolia desertgrassland, Otindag sandy land and the hilly and mountainous area in the north of Shanxiprovince. While the area of slightly degraded land was the largest and accounted for11.99%,which mainly distributed in the east of the Otindag sandy land and the south of Great Khingan.(7) Among the land degradation in the Beijing-Tianjin dust and sandstorm source regionfor recent10years, that mainly caused by human activity was68.05%, while the degradatedland caused by both of them accounted for31.95%. The other degradated land may bedegenerated much earlier, but its reason needs to be verified further. By contrast, the vegetationrecoverage mainly caused by human activity, it may be correlated to the ecologicalengineerings in the study area for recent years.