*2.1. GLASS LAI*

The GLASS LAI [10,28], available from http://glass-product.bnu.edu.cn/, is based on China's National High Technology Research and Development Program 863 key project 'Generation and application of global products of essential land variables'. A fused LAI dataset was generated from MODIS and CYCLOPES LAI products, and the MODIS and AVHRR surface reflectance was reprocessed to remove cloud and snow contamination. The training database was established over BELMANIP (Benchmark Land Multisite Analysis and Intercomparison of Products) sites, and then the general regression neural networks (GRNNs) were trained for each biome type to retrieve LAI from time-series reflectance data [29]. Then the entire year MODIS/AVHRR red and NIR reflectance data were input to the GRNNsto estimate one-year LAI pixel by pixel. In our study, we use the version 3 product. The product has different spatial resolutions at 5 km (about 0.05 degree at the equator) from 1981 to the present and 1 km after 2000, but the same time step of eight days for the whole temporal coverage.
