# Evidence of Carbon Uptake Associated with Vegetation Greening Trends in Eastern China
## 3 Results
### Trends in Regional XCO\({}_{2}\) Summer Drawdown
#### 3.2.1 Satellite Observed XCO\({}_{2}\) Trends after Removing Global Mean Growth  
As a first attempt, we removed the NOAA global mean XCO\({}_{2}\) growth rate from the GM-XCO\({}_{2}\) in order to calculate summer drawdown trends using the mean value of detrended GM-XCO\({}_{2}\) during the GP of each year as shown in Figure 5a. This removed remote influence, the long-term atmospheric growth rate, at each grid cell. Red grid cells with black outlines, indicating significant decreasing  
Figure 4: Growing period greening trends from 2003 to 2016 in (**a**) Moderate-Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and (**b**) AVHRR NDVI. Annual trends for the same years in (**c**) Advanced Very-High-Resolution Radiometer (AVHRR) leaf area index (LAI) and (**d**) tree canopy coverage. Increasing trends are in blue with decreasing trends in red, and grid cells with black outlines indicate trend significance using the Mann–Kendal test (\(p<0.05\)). All vegetation indices show significant greening in Eastern China, outlined in red. t trends, were observed in some parts of south China (\(-0.07\pm 0.05\) ppm yr\({}^{-1}\) for decreasing grid cells). Blue grid cells with black outlines, indicating significant increasing trends, \(0.05\pm 0.05\) ppm yr\({}^{-1}\), were observed in some urban regions like Beijing and Shanghai. Regions around cites like Beijing and Shanghai showed increasing XCO\({}_{2}\) at more extreme rates than the global mean. Blue grid cells indicate CO\({}_{2}\) emission increases (\(0.045\pm 0.055\) kg C m\({}^{-2}\) yr\({}^{-2}\)) near urban centers of Eastern Asia in Figure 5a. This is because fossil emissions have increased faster in Beijing and Shanghai than most other regions. Gridded trends in anthropogenic emissions from January 2003 to December 2016 from ODIAC are shown in Figure 5b. Therefore, it is necessary to remove the influence of the local urban CO\({}_{2}\) emission domes in order to isolate trends in local biospheric influence on XCO\({}_{2}\). .2.2 Satellite-Observed XCO\({}_{2}\) Trends after Removing Influence of the Urban CO\({}_{2}\) Dome  
In order to remove the influence of increasing anthropogenic emissions from urban centers in our study area, we tested four different spatially variable methods of detrending GM-XCO\({}_{2}\) observations: GM-XCO\({}_{2}\) fitting (Figure 6a), CT-XCO\({}_{2}\) fitting (Figure 6b), and GEOS-Chem simulated XCO\({}_{2}\) fitting at two different spatial scales: a coarse \(2\times 2.5\) degree lat/lon simulation and a high-resolution nested simulation for Eastern Asia (Figure 6c-d). All methods showed GM-XCO\({}_{2}\) residuals decreasing in many EC grid cells from 2003 to 2015 indicating greater CO\({}_{2}\) uptake during the GP. For the entire EC domain, detrending the XCO\({}_{2}\) time series of each grid by the long-term trend of each grid cell (GM-XCO\({}_{2}\) detrending using the full record including growing season and dormant season) resulted in a small trend in the corrected GM-XCO\({}_{2}\) during the GP, \(-0.058\pm 0.029\) ppm yr\({}^{-1}\). The standard deviation reported here is the variability in individual grid cell trends across the EC domain and not an indicator of within grid cell trend uncertainty. This is possible because the annual means and the GP drawdown only can have different trends as seasonal cycles change over time. Detrending using model simulations of XCO\({}_{2}\) from remote and local non-biospheric CO\({}_{2}\) fluxes resulted in larger GP CO\({}_{2}\) uptake trends: \(-0.084\pm 0.090\), \(-0.081\pm 0.088\), and \(-0.070\pm 0.093\) ppm yr\({}^{-1}\) (mean \(\pm\) 1 standard deviation in space), for CT-XCO\({}_{2}\) and GEOS-Chem coarse and fine resolution, respectively. Of all the grid cells, larger GP CO\({}_{2}\) uptake trends were observed in 80%, 79%, and 77% of the grid cells  
Figure 5: GM-XCO\({}_{2}\) trends from 2003 to 2015 in growing period corrected with NOAA annual increase (**a**).