Long-Term Variation of Global LAI and the Uncertainty: Analysis of the GEOV2 and Modis LAI Products

Abstract

This study investigates the long-term variation of global leaf area index (LAI) and their uncertainties based on an analysis of the most recent global GEOV2 and MODIS (V6.0) products from 2003 to 2018. The global LAI values, the product qualitative quality flags (QQFs) and quantitative quality indicators (QQIs) were analyzed to study their temporal trend. Results shows that the global GEOV2 and MODIS LAI increased from 2003 to 2018. Meanwhile, the GEOV2 product shows that the global LAI uncertainty (0.019/decade) and relative uncertainties (0.8%/decade) have also increased during the same period. Seasonally, both spring (MAM) and summer (JJA) have seen stronger increase in LAI, uncertainty and relative uncertainty from GEOV2. Among the biome types, the LAI increase mainly occur over the savanna regions, where the LAI uncertainty also increased swiftly (0.033/decade for GEOV2). The GEOV2 product shows that the LAI uncertainties for the evergreen broadleaf forest (EBF) increased abruptly since 2014, possibly because of the shift of satellite sensors. The global urban areas have observed a steady decrease in LAI. This study highlights the importance of global LAI uncertainty study and the information is critical for global environmental studies.