Comparison of Seasonal and Interannual Variations of Leaf Area Index from Satellite Data and a Dynamic Vegetation Model

Using Moderate Resolution Imaging Spectrometer (MODIS) and Global Inventory Monitoring and Modeling Studies (GIMMS) data, leaf area index (LAI) has been compared with the simulated results by a recently developed dynamic vegetation model, Interactive Canopy Model (ICM), which includes the carbon and nitrogen cycling processes of the ecosystem. Results show that ICM has the capability of reproducing the seasonal and interannual variations of the global vegetation. However, LAI was generally overestimated in the high and low latitudes but underestimated in the middle latitudes. The underestimations in mid-latitude are always followed by the vegetation sprout for the reason that modeled growth period lag behind the observed. The significant interannual variabilities and the spatial distributions of LAI are well captured by the model. But the simulated LAI exhibits larger variabilities than the observations in most areas except for some tropical regions. The temporal and spatial evolutions of the observed LAI are well simulated in low-latitudes. The bimodal distributions in seasonal variations of the tropical evergreen broadleaf trees and crops have not been well simulated. In addition, the model gives better results in the interannual variations of the boreal shrubs, savanna and deciduous needleleaf trees than other types of vegetation. And the simulated LAI in natural vegetation cases is better than that of crop in both seasonal and interannual time scales, which suggests that it is very important to incorporate the human interferences into the dynamic vegetation model.