The Forest Vegetation Change And Its Water Consumption Research In Chaobai River Basin Under The Back Ground Of Climate Change

To monitor the forest vegetation cover change and forest ecosystem water balance under the background of climate change in the Chaobai river basin. This study evaluated the climate change of Chaobai river basin in the nearly30years based on the meteorological data. It included the aspects of temperature, precipitation, evaporation and drought. Then applying the multi-source remote sensing data (AVHRR NDVI\MODIS NDVI\MODIS LAP\Landsat5TM) to analyze the vegetation interannual and during the year grewing feature during the period of1982to2012. And applying the SEBAL model to estimate the regional evaporation amount and combining the model with the FAO reference crop transpiration by evaporation and crop coefficient method to estimate the vegetation transpiration water consumption in different time scale. The conclusions showed that:(1)The Chaobai river basin had a warming trend since80s of last century. There were most light droughts from1980s to the early of2010s, and there were just two heavy droughts in the study area.The seasonal drought trend showed that the summer drought had an increasing trend in Chaohe area and Baihe area, and the other seasonal drought conditions had better trends. The frequency of Spring drought was the highest, followed by the winter drought. Autumn drought and summer drought occurred less, but they had a greater impact on the level of annual drought.(2) The inter-annual NDVI values showed a slight rise, but its fluctuation was big in the whole basin. It accounted for about90.43%of the total area where the vegetation situation got improved. The vegetation growth season was during April to October, and the change law of LAI in the year conformed to the law of Logistic.(3) The evaporation of forest vegetation in the different growth stages had large differences. This study estimated the annual ecological water consumption by expanding the vegetation coefficients to the whole growing season. The annual ecological water consumption of Banchengzi river basin was619.8mm, and the Hongmenchuan was510.4mm. The vegetation was severe water shortage in early stages of growth. And the coniferous forest ecological water demand was the most, then the broad-leaved forest and shrub. To make the forest play a better benefits on the water conservation it can promote the composite mode which included the forest and shrubs. The major driving factors of forest vegetation transpiration water consumption were LAI, temperature and altitude. The accuracy of ET quantity that SEBAL model estimated compared with the lysimeter observation data was87.9%. And the accuracy of the vegetation coefficients that calculated by SEBAL model and P-M formula in this paper was74.5%.(4) In the whole basin, with the rising of drought level, the yearly average values of NDVI were falling down and the correlations between M values and NDVI were becoming stronger. And the vegetation growth will becoming deteriorated along with the drought conditions getting intensified. The yearly maximum of NDVI was most affected by the summer climate in the same year and the autumn climate of the last year. The inter-annual variation trends of M indexes and NDVI were very similar, but there were some inconsistencies between drought and inter-annual variability of vegetation, which were caused by human activities, different surface vegetation types or other natural and human factors.