To assess the accuracy of the land surface dataset currently used in CLM2 (referred as the old data thereafter), we create a new land surface dataset from the latest MODIS land products using similar procedures as described by Bonan et al. [2002b].   

We aggregate MODIS 500m collection 3 Global Vegetation Continuous Fields (VCF) [DeFries et al., 1999] from 2000-2001 to generate 1 km FVC data. The VCF data contain percent of tree cover (tall trees), herbaceous cover (shrubs and grasses) and bare. The sum of these three components equals 100% ground cover. The FVC data is calculated as a sum of percentage of tree canopy cover and herbaceous cover.

We generate a 15 PFT dataset at 0.5°x 0.5° resolution from the MODIS 1 km PFT and IGBP land cover maps. The MODIS PFT map consists of 7 primary PFTs, needleleaf evergreen or deciduous tree, broadleaf evergreen or deciduous tree, shrub, grass and crop. It is expanded to 15 PFTs based on climate rules [Bonan et al., 2002b]. Since the current VCF data does not distinguish between evergreen versus deciduous and broadleaf versus needleleaf for the tree cover or shrub versus grass for the herbaceous cover, we assume that each 1 km pixel has only one PFT and its abundance equals its FVC. The bare fraction is 1-FVC. The 1-km data were aggregated to grid cells at 0.5° resolution by averaging the 1-km percentages per 0.5° grid cell, which normalized the percent of each grid cell covered by a particular PFT by the vegetated area [Bonan et al., 2002b]. The bare ground in each grid cell is always considered to be the cumulative canopy opening.

We generate an monthly LAI dataset for every PFT at 0.5° resolution from two and half years of collection 4 MODIS 1-km LAI data [Myneni et al., 2003] in 2000, 2001, and January through June in 2003. First, LAI at 1-km was divided by the FVC to produce LAI with respect to vegetated area only. Second, evergreen needleleaf PFTs were adjusted to be no less than 70% of their maximum LAI to correct the MODIS biases of lower winter LAI values in the presence of snow [Tian et al., 2004]. It is no longer necessary to adjust the evergreen broadleaf LAI since the current MODIS data has substantially improved LAI retrievals in tropical and subtropical regions compared to AVHRR. Third, for each PFT, a pure PFT LAI was estimated at a 0.5° grid cell by averaging only the LAIs over 1-km pixels whose abundance of the PFT is greater than 60%.

New land surface data set is available for use in CLM2. Please contact Yuhong Tian (ytian@eas.gatech.edu) for downloading information.

 Tian, Y., Dickinson, R.E., Zhou, L., Myneni, R.B., Friedl, M., Schaaf, C.B., Carroll, M.,  and Gao, F., Land boundary conditions from MODIS data and consequences for the albedo of a climate model, Geophy. Res. Lett., accepted, 2004.