# Contribution of Climate Change and Grazing on Carbon Dynamics in Central Asian Pasturelands
## 3 Results
### Spatio-Temporal Variations in NEE  
Simulated annual carbon fluxes over the pasturelands from 1981 to 2014, from three versions of reanalysis data, are shown in Figure 4. The model simulated an annual total terrestrial NEE of \(-0.06\)\(\pm\) 0.04 Pg C year\({}^{-1}\), which means that pasturelands in Central Asia released 2.10 \(\pm\) 1.60 Pg C in the past 36 years. We compared the average state (1981-2014) of the terrestrial carbon cycle among climate datasets (Figure 5), and the NEE differed among the simulations. The highest values were obtained with the CFSR (\(-15.42\) g C m\({}^{-2}\) year\({}^{-1}\)) and the lowest with the MERRA (\(-23.69\) g C m\({}^{-2}\) year\({}^{-1}\)) dataset.  
In response to climate change and grazing effects, regional NEE estimated by the three reanalysis datasets increased 0.43 g C m\({}^{-2}\) year\({}^{-1}\) (R\({}^{2}\) = 0.30) in the CFSR, 0.40 g C m\({}^{-2}\) year\({}^{-1}\) (R\({}^{2}\) = 0.20) in ERA-Interim, and 0.54 g C m\({}^{-2}\) year\({}^{-1}\) (R\({}^{2}\) = 0.35) for the MERRA, respectively. Precipitation is more significantly related with NEE interannual variability than temperature at the regional scale (Figure 4).  
Figures 5 and 6 show the spatial distribution of annual mean values of the NEE in DG, TG, and FM. The three datasets all agreed that DG, TG, and FM were C sources during the study period, as well as the strongest carbon loss in TG (\(-35.47\)\(\pm\) 7.75 g C m\({}^{-2}\) year\({}^{-1}\)). The simulation results under the MERRA showed the largest carbon release in all the three grassland types, while the CFSR drove the weakest carbon source. In addition, the NEE from the three versions of the reanalysis data differed significantly. In DG and TG regions, CFSR data performed differently with the other two, by more than 35% on average. In contrast, there was a smaller difference in FM from the CFSR and ERA-Interim (Table 3).  
Figure 2: Changes in annual mean air temperature (**a**) and annual total precipitation (**b**) in Central Asia from 1981 to 2014.  
Figure 3: Comparison of the spatial patterns of precipitation and annual mean temperature during 1981–2014. (**a**,**c**,**e**) are the mean values of annual total precipitation calculated from the CFSR, ERA-Interim, and the MERRA, respectively. (**b**,**d**,**f**) are the average annual mean air temperature derived from the CFSR, ERA-Interim, and the MERRA, respectively.  
Figure 4: Changes in NEE, annual precipitation, and grazing intensity in Central Asia from 1981 to 2014: (**a**) Dry Grassland (DG), (**b**) Temperate Grassland (TG), (**c**) Forest Meadow (FM), and (**d**) Central Asia. Positive values of NEE indicate carbon sink and the negative indicate carbon source. NEE was calculated from the averaged results of the three sets of simulation results.  
Figure 5: Comparison of the averaged NEE of different grassland types during 1981–2014, forced by the three sets of reanalysis data: (**a**) Dry Grassland (DG), (**b**) Temperate Grassland (TG), (**c**) Forest Meadow (FM), and (**d**) Central Asia. AVG: calculated from the averaged results of three sets of simulation results. The squares and asterisks represent the medians and outliers, respectively. The blocks are determined by the 25 th and 75 th percentiles, and the whiskers are based on the 5 th and 95 th percentiles.