Impacts of land use and climate change on the net primary productivity in XinJiang based on remote sensing

Abstract

Arid and semi-arid ecosystems exhibit a spatially complex biogeophysical structure. According to arid western special climate-vegetation characters, using the remote sensing spectral mixture analysis. The study developed a modified production efficiency model Net Primary Productivity-Geography Processing Ecology Model (NPP-GPEM) appropriate for the arid area at regional scale based on the concept of radiation use efficiency. Combined with recent historical period climate data and two periods of land use data sets from remote sensing data, we test the net primary productivity (NPP) data sets over last 20 years in XinJiang of the North China modelled by the NPP-GPEM with the satellite data-driven for detecting the wide spread spatial temporal characteristics of the impacts of climate and land use change impact with the regional NPP. Our results shows that over past 20 years, the average annual temperature in the research region has remarkably increased by more than 0.056°C, but over the same period, there has been a 0.635mm increase in annual precipitation and increase in NPP by an annual rate of 0.142TgC. Taking use of 16 land covers of Xinjiang which was carried on the calculation of the matrix transfer, the study got the matrix of the NPP changes over past 20 years. The result found that the quicker trend increasing is the others woodlands (the 5.51gC/m2/yr) and the oasis farmland (4.32 gC/m2/yr). The pasture area is the biggest to about 29.3% of total area, the pasture growth is smaller than others, but its increase to the contribution rate of the annual NPP in the whole land ecosystem system biggest is pasture and agricultures to land use covers, that had the total annual NPP increase with 52.2% and 19.9% of the quantity respectively, the plant cover is only the shrub pant which has a absolute decrease ecosystem system in the type (- 14.39gC/m2); In fine, the paper mainly reveals the dissimilarities and conversion among the pasture, farmland, woodland and different covered pasture and other types. The correlation analysis between annual NPP and annual precipitation was highly consistent with plant cover spatially (R2=0.64, P<0.01) in the overall XinJiang, and the northern of XingJiang is better than the southern of it, and the correlation coefficient changes with the changes of vegetation types and different regions. The analysis revealed that the climate changes dominate the impacts on the NPP in the whole study region. However, land use plays a dominative role in the areas with land cover changes. Over past 20 years, the NPP in the whole study region remarkably increased due to obvious precipitation decrease and temperature rise. Between two periods of land use (about 10 years), the changes in climate are predicted to cause increases in NPP, and combined impacts of climate changes and land use to cause to increase in NPP.