## 3 Results
### Dynamic Change in Ecosystem GPPs  
Recalling that the GLASS-GPP showed the best performance for observed GPP, we present the magnitude of changes in the GLASS-GPP time series and their statistical significance using the \(Z\)-statistic. As shown in Figure 3, the \(Z\)-statistic for the majority of the GPP time series was 1.95 or more (\(p<0.05\)). GLASS-GPP showed a significant increasing trend in Turkey, west Iran, and Syria, while the western portions of Egypt and south Saudi Arabia witnessed significant negative trends (Figure 3). As illustrated in Figure 3, the annual GLASS-GPP exhibited significant trends over the whole domain and had slope values ranging from \(-1\) to 60 gCm\({}^{-2}\) yr\({}^{-1}\). The greatest changes were observed in the Nile Delta and along the Nile River, which had values ranging from 7.5 to 60 gCm\({}^{-2}\) yr\({}^{-1}\). Conversely, changes in Egypt's eastern and western deserts were less pronounced and had values ranging from 0 to 3.5 gCm\({}^{-2}\) yr\({}^{-1}\). In Turkey, the changes were in the range of 3.5-15 gCm\({}^{-2}\) yr\({}^{-1}\) but were much weaker (\(<\)3.5 gCm\({}^{-2}\) yr\({}^{-1}\)) in central Turkey. In Saudi Arabia, changes in GLASS-GPP varied from \(-1\) to 3.5 gCm\({}^{-2}\) yr\({}^{-1}\) compared to a range of \(-1\) to 3.5 gCm\({}^{-2}\) yr\({}^{-1}\) in Oman, Yemen, and the eastern part of Iran.  
However, for more insights into the regional trends of GPP across the region, we also looked at changes in GPP using the different GPP datasets. This comparison was restricted to the common period (1982-2016) for all products. Moreover, we looked at the short-term changes in GPP by dividing the entire study period into two identical short sub-periods: 1982-1999 and 2000-2016.  
For almost all products, the regional GPP in the Middle East showed an increasing trend between 1982 and 2016 except for FluxCom-GPP, which suggested a decreasing trend (Figure 4). Notably, the GLASS-GPP dataset showed a significant upward trend from 1982 to 1999 and then a decreasing trend from 2000 to 2016. The highest GLASS-GPP value was noted in 2013 (1.53 PgC), while the lowest was observed in 1989 (1.09 PgC) followed by 2008 (1.23 PgC). In contrast, the GIMMS-GPP's series slope was +0.0026 PgC yr\({}^{-1}\) (\(p<\) 0.05) for the period of 1982 to 1999; it then showed a significant increasing trend after 2000 to +0.0052 PgC yr\({}^{-1}\). The highest GPP value was observed in 2016 (0.709 PgC), while the lowest was seen in 2008 (0.613 PgC).  
In comparison to other products, the VPM-GPP showed the highest increasing magnitude over the study period of +0.019 PgC yr\({}^{-1}\) (\(p<\) 0.05); the highest value was recorded in 2016 (1.57 PgC) and the lowest in 1982 (1.116 PgC) (Figure 4). Interestingly, the datasets  
Figure 4: Temporal trends of the regional carbon stocks (in PgC yr\({}^{-1}\)) for the Middle East between 1982 and 2016. 1 PgC = 10\({}^{15}\) gC. Grouped bars on the bottom row indicate the magnitude of change for the two short sub-periods (1982–1999 and 2000–2016). The black lines are the statistical confidence interval (95%) of the regression lines.  
based on machine learning models (e.g., FluxCom-GPP) showed the least inter-annual variability amongst all of the products.  
Based on several GPP products, our findings showed a significant variation in the spatio-temporal trends of the GPP in the Middle East (Figure 5). Even though there was some consistency in the trend patterns across several GPP datasets for some products, we found significant variations in the trend values across these GPP datasets. As presented in Figure 5, a significantly increasing trend in GPP was recorded in the northern parts of the study area between 1982 and 2016 as shown by the GLASS, GIMMS, and VPN models. In contrast, a significantly decreasing trend was detected in the central and southern parts of the study area.