Estimation Of The Vegetation Net Primary Productivity Based On CASA Model In Gan River Basin

Based on energy efficiency model CASA (Carnegie-Ames-Stanford Approach), using1998-2012annual SPOT-VEGETATION NDVI data in Gan River Basin, combined withmeteorological data, the land cover data and soil texture data in the same period, we estimatedthe vegetation NPP during the15-year period in Gan River Basin, and analyzed temporal andspatial distribution characteristic of vegetationNPP and the correlation between it and climaticfactors inGan River Basin.The major conclusions are as follows:(1)Spatial distribution of annual vegetation NPP in Gan River Basin from1998to2012appear obvious differences, while the maximum NPP value is1264gC/m2,and annual NPP is758.88gC/m2/a. The highest cumulative NPP value is forest ecosystem, which is followed byfarmecosystem, and the grassland ecosystem isthe minimum.(2)The NPP of different vegetation types in Gan River Basin are quite different. Thelargest average NPP units is the forest ecosystem, the annual NPP of which is745.9gC/m2,followed by farmland, with an average annual NPP is745gC/m2, then is the shrub and grass,annual NPP of which were570gC/m2and501gC/m2separately.(3)From1998to2012the average NPP in Gan River Basin shows an overall steadyincrease trend, which the lowest value appears in2003, that is664.73gC/m2/a; and themaximum appears in2002, that is gC/m2/a. In the aspect of seasonal variations, the averageNPP in each spring (March to May) is46.26gC/m2/season, in summer(June to August) is114.75gC/m2/season, in autumn (September to November) is56.21gC/m2/season, and inwinter (December to February) is7.74gC/m2/season.(4)The month NPP for each vegetation type appear obvious single peak curvecharacteristic.The changing characteristics of the seasonal changes with the seasons andappears more obvious. NPP values of different vegetation types in July reached a maximumpeak, which in January and December reached the minimum.(5)Vegetation NPP inGan River Basin was negatively correlated with annual averagetemperature, and the partial correlation coefficient between the NPP and the average annualtemperature was-0.22throughout the study area. The area in which NPP was positivelycorrelated with mean annual temperature accounts for about16.42%of the totalvegetationarea, and the vegetation NPP in the region increases with increasing temperature; the area inwhich NPP was negatively correlated with average annual temperature accounts for83.58%of the total vegetation area, and the vegetation NPP decreases with increasing temperature.Vegetation NPP in Gan River Basin was positively correlated with annual precipitation, andpartial correlation coefficient between average NPP and annual precipitation was0.12 throughout the study area. The area of which NPP was positively correlated with annualprecipitation is about71.03%of the total vegetation area, where NPP of typical grasslandincreaseswith precipitation; the area of which NPP was negatively correlated with annualprecipitation accounted for28.97%of the total vegetation area, where NPP decreased withprecipitation decreasing.