## 3 Results
### iWUE* and LUE Trend during 1982-2010
#### 3.2.3 fAPAR3g, MTE-GPP and MTE-ET Trend during 1982-2010  
To better understand the iWUE* and LUE trends, we analyzed the trends of fAPAR, GPP and ET separately. The comparison between the simulations and data-products for fAPAR, GPP and ET trends is shown in Figure 5. Both GIMMS satellite data and the MTE-GPP show positive trends (at 95% CI) over the northern savannahs, especially in West Africa for the MTE product. For example, fAPAR3g shows a robust and positive trend over the northern savannahs by 4% per decade (Figure 5A). However, the fAPAR3g trend calculated from the annual values does not show a significant trend during 1982-2010 over the Sahelian band, probably due to the compensation of trends between wet and dry seasons, especially for the last decade (fAPAR3g has a negative trend in dry season during 2000-2010 over the  
Figure 3: 1982–2010 trends of iWUE* (% of iWUE*): **(A)** iWUE* calculated from MTE-GPP and MTE-ET product with VPD from WFDEI CF; **(B)** iWUE* trend obtained with the ORCHIDEE 11-layer version and **(C)** the 2-layer version. Same color code than Figure 3.  
Sahel). The GPP from the MTE product shows a large positive trend at 95% CI over the northern savannah, particularly over the West African and Sahelian zone over which MTE-GPP increases by 25% per decade (Figure 5 B). A positive and strong MTE-ET trend at 95% CI is found over West Africa (more than 10% per decade over the Senegal) and the southern Sahel (4% per decade over the Guinea band). Over the African southern savannah, ET increases significantly by 15% per decade during 1982-2010. Note however the negative trend in both MTE-ET and MTE-GPP over Tanzania with values of about \(-\)5% of decrease per decade.  
Figure 4: Same as Figure 4 for 1982–2010 trends of LUE (% of LUE). **(A)** MTE-LUE trend; **(B)** S1-LUE trend; **(C)** S2-LUE trend.  
Figure 5: 1982–2010 trend of fAPAR (left column), GPP (middle column) and ET (right column). The first line is **(A)** GIMMS-fAPAR3g satellite observations, **(B)** MTE- GPP, and **(C)** MTE-ET data-products. The middle line is **(D)** simulated fAPAR, **(E)** GPP and **(F)** ET with the ORCHIDEE 11-layer simulation driven by variable CO\({}_{2}\) and WFDEI climate forcing (see text). The bottom line is **(G)** simulated fAPAR, **(H)** GPP and **(I)** ET with the 2-layers version. Trends are expressed in % of the each variable. The color table represent negative or positive trends statistically significant at 95% confidence interval (CI). Slate (dark) grey and grey represent respectively pixels with positive and negative trends with a CI lower than 95%.  
Simulation results from both versions of ORCHIDEE (11-layer and 2-layer) show comparable geographical patterns of fAPAR, GPP and ET trends during 1982-2010. Contrary to the GIMMS-fAPAR3g trends, the ORCHIDEE model shows no significant temporal trend from annual fAPAR over a large part of Africa, regardless of the soil hydrology scheme. Areas of simulated fAPAR trend at 95% CI are patchy and include only few grid cells (Figure 5D,G). In comparison with MTE-GPP product, ORCHIDEE only simulates positive GPP trend at 95% CI over central African forest (4% per decade) for both soil hydrology schemes, and does not match the MTE-GPP product. However, ORCHIDEE simulates strong and positive GPP trend in some grid cells over the African southern savannahs (20% per decade) consistently with MTE-GPP (Figure 5E,H). As for GPP, the simulated ET trend does not match the geographical pattern of MTE-ET trend over the northern savannah. In contrast, the model better matches the MTE-ET trends over the African southern savannahs (Figure 5F,I). ORCHIDEE simulates a negative ET trend during 1982-2010 over the southern African forests (Zambia and Zimbabwe) of -4% per decade. Over the African southern savannahs, ORCHIDEE simulates a positive and strong ET trend during 1982-2010 in a few grid cells (15% of increase per decade).