Research On The Interannual Variation Of Forest Cover And Albedo In Northern China

Northern China (above the 35 degrees Northern latitude) with its vast landmass has scarce vegetation and fragile ecological envionment. Ecological security in this region and even in the whole world is affected by the variations of forest coverage in this area. Albedo of different types of forest coverage has obvious space-time difference, the variations of which will affect the entire energy balance of the earth-atmosphere system, thus impact on climate change. This paper tries to evaluate the result of ecological construction in northern China in recent years, and explore the general regularity between the variations of forest coverage and albedo.In this study, MODIS product data of land cover types and albedo in four typical phases during 2003 to 2012 was collected to analysis the variations of different forest cover types, and to study the spatial distribution and variation of forest in the area. Albedo fornew and degenerate forest of different coverage types were discussed respectively using data in typical season. The results showed that:(1) A growing trend appears in the forest coverage of northern China overall. Forest increasing rate is 3.017%, the newly grew forest mainly come from the farmland (46.5%), grassland (39.6%), bare soil (13%), and evergreen coniferous forest has the fastest growth rate, while mixed forest has the largest growth amount. Forest degradation rate is 1.447%, the forest degradation mainly transformed into grassland (53.9%), farmland (39.4%) and bare soil (5.7%);(2) The boreal forest coverage rate increased from 8.51% to 10.27% with a net increase of 1.57% during the 10 years. Forest distribution of northern China mainly exists in big and small Xing’an mountain and Changbai Mountain area, followed by Beijing and surrounding provinces, Shanxi, Shaanxi Gansu Ningxia and western Xinjiang area. Forest coverage rate showed a gradual upward trend in the temperate monsoon climate zone, while increased and reached the peak in 2008, and then began to slow down in the temperate continental climate zone and the mountain plateau climate zone. Overall, forest coverage was significantly higher in 2012 than that in 2003;(3) A decreasing trend appears in the albedo of northern China during the ten years as a whole, which shows a negative correlation with the forest coverage change. Albedo in the temperate monsoon climate zone changes slightly, but remains unchanged at the level about 0.15; albedo in the temperate continental climate zone and the mountain plateau climate zone decreased year by year, at about 0.19-0.2;(4) Forest increase and degradation mainly occur between different types of vegetation coverage, so albedo variations of unchanged forest, increased forest and degraded forest over the same period in summer during 10 years were small. Reduction effect on albedo was obvious when the coverage types changed from others to evergreen coniferous forest and shrub, indicating that evergreen coniferous forest and shrub have a significant effect on the decrease of albedo, which means that they have better ecological functions from the perspective of energy balance.