Fig.4. Consequences of biased input data on LUE-NDWI GPP at
global scale. (a) the mean annual GPP from 2000 to 2018 after data
correction. (b) the difference of mean annual GPP from 2000 to 2018,
GPPuncorrected – GPPcorrected. Symbols
indicate various levels of difference: ‘–’: -50%-(-30%), ‘-’:
-30%-(-10%), ‘±’: -10%-10%, ‘+’: 10%-30%, ‘++’: 30%-50%. The
inset bar chart shows the global distribution of the difference
proportions. (c) Comparison of annual global GPP estimates from various
models. The number after each model’s name in parentheses is the number
of years of the model in the interquartile range (IQR), indicated by the
shaded region. LUE-NDWI and LUE-NDWI1 are GPP estimated by LUE-NDWI with
corrected and uncorrected input data, respectively. (d) Boxplot of
annual GPP values during the study period for each model. (e) Trends of
annual GPP (Pg C yr−1) by model. Symbols of LUE models
are in black, machine learning models in green, biophysical models in
blue.