Space-time Variety Characteristics And Eco-environment Effect Of Permafrost In The Source Region Of The Yellow River

In the source region of the Yellow River, its hydrological and ecologicalenvironment, such as lakes、 wetlands shrinking, rivers dry-up, grass landdesertification or “black-soil patch”, have occurred in recent decades, especially sincethe1980s. Preliminary studies of these phenomena have shown that permafrost, aspecial aquitard, has a great impact on regional hydrological cycle andeco-environmental existent. In order to understand the causes of ecologicalenvironment variation, the research carried out includes the following studies.We employed the basic theory of eco-hydrology, mathematical calculations andGeographic Information System software to analyze the characteristics of climatechange, vegetation indices, annual and future temperature and moisture in seasonalactive-layer by making use of the meteorological data, remote sensing data. Base onthese studies, we simulated the spatial and temporal characteristics of active layerthickness. We also studied the correlation between Normalized Difference VegetationIndex (NDVI) and active layer thickness, temperature and precipitation along with thesignificance level of each influencing factor over a range of spatial temporal scale.Some results can be reached.(1) The annual average air temperature in the source region has been rising at therate of0.03℃/a from1955to2011. Since the end of the1990s the rising rate evenreached0.06℃/a. Precipitation changed slightly during the same time.(2) Based on the variation of annual temperature and moisture in active layer, themodeling results that the active layer thickness increased from about2.5m in2000to2.8m in2011at a rate of2.5cm/a. The active layer thickness will reach3.5m after20years at a rate of3.5cm/a, while the increase rate of columnar moisture per unitarea will be4.5cm/a under a warming rate of0.04℃/a assumed.(3) From2000to2011, the area of increasing and stable vegetation with positiveslope of NDVI occupies89.2%of the region. On the contrary, the degradation areaswith negative NDVI slopes are about4.64%of the total area and mainly located insouth of the two largest lakes, Yueguzonglie basin in the west, upstream of the Yellow River and north of the Gyaring Lake.(4) By analyzing the correlation between NDVI from2000to2011and activelayer thickness、temperature and precipitation, it was found that rainfall is the mainimpact factor on the NDVI, the secondary facts are active layer thickness andtemperature sequentially. Analysis results on significance level of each factor onNDVI showed that active layer thickness dominating the vegetation variation on aspatial scale, meanwhile, the impacts of temperature and precipitation on NDVI varieswith altitude. When elevation is within4630~4850m, precipitation plays moreimportant role on NDVI, while the dominating impact may be temperature out of thealtitude range.(5) Utilizing the surface frost number0.5,0.8respectively as the delimitationcriterion to partition permafrost, transitional frozen soil and seasonal frozen soil, theresults modeled showed that the area of permafrost is about19850km2takes up morethan90percent of the whole area in2011. The total area of transitional frozen soil andseasonal frozen soil, located around Madoi County and the two big lakes, occupiedabout494km2,2.3percent of the region which matched well with the findings of fieldinvestigation. Furthermore, the permafrost area modeled will reduce about220km2and the area of seasonal frozen soil will increase65km2under a warming rate of0.04℃/a in the next20years.