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Water use efficiency of China's terrestrial ecosystems and responses to drought.

Liu Y, Xiao J, Ju W, Zhou Y, Wang S, Wu X - Sci Rep (2015)

Bottom Line: Droughts usually increased annual WUE in Northeast China and central Inner Mongolia but decreased annual WUE in central China. "Turning-points" were observed for southern China where moderate and extreme droughts reduced annual WUE and severe drought slightly increased annual WUE.The cumulative lagged effect of drought on monthly WUE varied by region.WUE is expected to continue to change under future climate change particularly as drought is projected to increase in both frequency and severity.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Key Laboratory of Agricultural Meteorology, School of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing, 210044, China.

ABSTRACT
Water use efficiency (WUE) measures the trade-off between carbon gain and water loss of terrestrial ecosystems, and better understanding its dynamics and controlling factors is essential for predicting ecosystem responses to climate change. We assessed the magnitude, spatial patterns, and trends of WUE of China's terrestrial ecosystems and its responses to drought using a process-based ecosystem model. During the period from 2000 to 2011, the national average annual WUE (net primary productivity (NPP)/evapotranspiration (ET)) of China was 0.79 g C kg(-1) H2O. Annual WUE decreased in the southern regions because of the decrease in NPP and the increase in ET and increased in most northern regions mainly because of the increase in NPP. Droughts usually increased annual WUE in Northeast China and central Inner Mongolia but decreased annual WUE in central China. "Turning-points" were observed for southern China where moderate and extreme droughts reduced annual WUE and severe drought slightly increased annual WUE. The cumulative lagged effect of drought on monthly WUE varied by region. Our findings have implications for ecosystem management and climate policy making. WUE is expected to continue to change under future climate change particularly as drought is projected to increase in both frequency and severity.

No MeSH data available.


Validation of BEPS simulated annual WUE against WUE derived from EC measurements.The error bars indicate standard deviation of annual WUE for each site.
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f7: Validation of BEPS simulated annual WUE against WUE derived from EC measurements.The error bars indicate standard deviation of annual WUE for each site.

Mentions: In this study, we further used EC data from 35 sites (13 forest sites, 14 grassland sites, 5 cropland sites, and 3 wetland sites)11253455 to evaluate the performance of BEPS in simulating WUE across China (Fig. 6 and Table S2). The annual MODIS NPP and ET products were also used to calculate WUE and to compare against annual WUE simulated by the BEPS model. The NEP data observed at EC sites were partitioned into GPP and ER. In order to calculate tower WUE (NPP/ET), tower GPP should be converted to NPP. As the residual of GPP minus autotrophic respiration, NPP can be treated as a fixed fraction of GPP at longer time step with uncertainties3536. Mean values of NPP/GPP over the EC tower sites simulated by BPES are 0.43 ± 0.10 for forest, 0.48 ± 0.07 for grassland, 0.54 ± 0.06 for cropland, and 0.54 ± 0.01 for wetland, respectively. These values were consistent with the previous observation synthesis and modeling studies3536. We converted tower GPP to NPP using the ratio of NPP to GPP simulated by BEPS for each site and then compared the tower-derived annual WUE with modeled WUE across the sites. The comparison showed that the BEPS model could simulate the annual WUE across sites fairly well (Y = 0.78X + 0.12, R2 = 0.93, p < 0.0001) (Fig. 7). The BEPS model slightly overestimated WUE in the lower end of the range (<0.4 g C kg−1 H2O) and slightly underestimated WUE in the higher end of the range (>0.8 g C kg−1 H2O). The ratios of NPP to GPP simulated by BEPS were used to convert tower-based GPP to NPP. To provide a more independent validation, we also validated modeled GPP/ET using EC-derived GPP/ET. The comparison showed that BEPS simulated WUE with the definition of GPP/ET fairly well for 35 EC tower sites across China (Fig. S13).


Water use efficiency of China's terrestrial ecosystems and responses to drought.

Liu Y, Xiao J, Ju W, Zhou Y, Wang S, Wu X - Sci Rep (2015)

Validation of BEPS simulated annual WUE against WUE derived from EC measurements.The error bars indicate standard deviation of annual WUE for each site.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4562296&req=5

f7: Validation of BEPS simulated annual WUE against WUE derived from EC measurements.The error bars indicate standard deviation of annual WUE for each site.
Mentions: In this study, we further used EC data from 35 sites (13 forest sites, 14 grassland sites, 5 cropland sites, and 3 wetland sites)11253455 to evaluate the performance of BEPS in simulating WUE across China (Fig. 6 and Table S2). The annual MODIS NPP and ET products were also used to calculate WUE and to compare against annual WUE simulated by the BEPS model. The NEP data observed at EC sites were partitioned into GPP and ER. In order to calculate tower WUE (NPP/ET), tower GPP should be converted to NPP. As the residual of GPP minus autotrophic respiration, NPP can be treated as a fixed fraction of GPP at longer time step with uncertainties3536. Mean values of NPP/GPP over the EC tower sites simulated by BPES are 0.43 ± 0.10 for forest, 0.48 ± 0.07 for grassland, 0.54 ± 0.06 for cropland, and 0.54 ± 0.01 for wetland, respectively. These values were consistent with the previous observation synthesis and modeling studies3536. We converted tower GPP to NPP using the ratio of NPP to GPP simulated by BEPS for each site and then compared the tower-derived annual WUE with modeled WUE across the sites. The comparison showed that the BEPS model could simulate the annual WUE across sites fairly well (Y = 0.78X + 0.12, R2 = 0.93, p < 0.0001) (Fig. 7). The BEPS model slightly overestimated WUE in the lower end of the range (<0.4 g C kg−1 H2O) and slightly underestimated WUE in the higher end of the range (>0.8 g C kg−1 H2O). The ratios of NPP to GPP simulated by BEPS were used to convert tower-based GPP to NPP. To provide a more independent validation, we also validated modeled GPP/ET using EC-derived GPP/ET. The comparison showed that BEPS simulated WUE with the definition of GPP/ET fairly well for 35 EC tower sites across China (Fig. S13).

Bottom Line: Droughts usually increased annual WUE in Northeast China and central Inner Mongolia but decreased annual WUE in central China. "Turning-points" were observed for southern China where moderate and extreme droughts reduced annual WUE and severe drought slightly increased annual WUE.The cumulative lagged effect of drought on monthly WUE varied by region.WUE is expected to continue to change under future climate change particularly as drought is projected to increase in both frequency and severity.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Key Laboratory of Agricultural Meteorology, School of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing, 210044, China.

ABSTRACT
Water use efficiency (WUE) measures the trade-off between carbon gain and water loss of terrestrial ecosystems, and better understanding its dynamics and controlling factors is essential for predicting ecosystem responses to climate change. We assessed the magnitude, spatial patterns, and trends of WUE of China's terrestrial ecosystems and its responses to drought using a process-based ecosystem model. During the period from 2000 to 2011, the national average annual WUE (net primary productivity (NPP)/evapotranspiration (ET)) of China was 0.79 g C kg(-1) H2O. Annual WUE decreased in the southern regions because of the decrease in NPP and the increase in ET and increased in most northern regions mainly because of the increase in NPP. Droughts usually increased annual WUE in Northeast China and central Inner Mongolia but decreased annual WUE in central China. "Turning-points" were observed for southern China where moderate and extreme droughts reduced annual WUE and severe drought slightly increased annual WUE. The cumulative lagged effect of drought on monthly WUE varied by region. Our findings have implications for ecosystem management and climate policy making. WUE is expected to continue to change under future climate change particularly as drought is projected to increase in both frequency and severity.

No MeSH data available.