## Results
### Seasonal and Interannual Variabilities of Modeled and Observed Carbon Dioxide and Water Fluxes
#### 3.2.1 Day-to-Day and Seasonal CO\({}_{2}\) and Water Fluxes Variability
The removal of aboveground biomass by harvesting or grazing led to sharp reductions of the transpiration rates, partially compensated by the increase in soil transpiration caused by an increase of solar radiation reaching--and higher temperature at--the soil surface. Grazing events greatly affected GPP and ET (Figure 7a,d) and caused massive spikes in modeled ER due to cattle respiration (Figure 7b). Similarly to the mowed paddock discussed above, the removal of photosynthesizing biomass by grazing animal caused an important subsequent reduction in carbon assimilation rates (GPP). However, in contrast to harvest events which were sudden and restricted to single days, the removal of biomass by dairy cows was progressive and spread over several consecutive days (on average five days). GPP reductions were therefore not as abrupt as for the mowed grassland (Figures 6a, 7a and A1) and generally, postgrazing daily modeled and observed GPP values agreed well and remained higher than postharvest values, which most likely resulted from the extent of biomass removal that differ between the two treatments. Day to day variability and seasonality of ER and NEE of the grazed paddock were also reasonably well captured by CenW (Figure 7b,c), but there were large discrepancies between these two daily modeled and observed variables during most of the grazing events. These differences resulted from the fact that the CenW model specifically simulated grazers' respiration rates based on measured amounts of vegetation ingested, which caused the large pulses in modeled ER and NEE. According to  
Figure 6: Time series of modeled (black line) and observed (red dots) daily carbon fluxes (**a**) GPP, (**b**) ER, and (**c**) NEE, and water fluxes (**d**) ET for the mowed grassland site. Vertical green lines represent mowing events. CenW simulations, the grazing animal respiration rate is 4.15 kg C head\({}^{-1}\) d\({}^{-1}\) (4 \(\upmu\)mol CO\({}_{2}\) head\({}^{-1}\) s\({}^{-1}\)). In some cases, such pulses were visible but much smaller in the eddy covariance measurements than in the model. Measurements could only record what happened within the flux footprint, which varied with wind speed and direction while the CenW model simulated the whole paddock. If all dairy cows were not inside the footprint at any given time, it would have been impossible for the EC tower to measure total grazing animals' respiration while it was fully accounted for in the CenW model. At other times, a large number of cows might have been present within the flux footprint and their respiration would have been captured by the EC system. However, because this rate could have been an order of magnitude higher than the base respiratory carbon flux from the soil and pasture [56] the corresponding data could have been filtered out during the processing of EC fluxes. If the resultant data gaps during grazing events were filled using the traditional Reichstein gap-filling and partitioning algorithms it could have resulted in gaps being filled based on data collected during periods in the preceding and following week when there were no cows present within the flux footprint. Figure 7: Time series of modeled (black line) and observed (red dots) daily carbon fluxes and water fluxes (**a**) GPP, (**b**) ER, (**c**) NEE, and (**d**) ET for the grazed grassland site. Vertical green lines represent grazing events. 2.2 Interannual Variability of CenW Modeled and EC Measurements of CO\({}_{2}\) and H\({}_{2}\)O Fluxes  
Interannual Variations in Mean Daily Fluxes  
Generally, daily modeled and observed fluxes averaged over the five years of the study agreed very well for the mowed grassland site, as well as their interannual variations (+/- 1 SE from the 5-year daily averages). This is highlighted in Figure 8 by error bars (for EC observed fluxes) and yellow area (for CenW modeled fluxes) and confirms that the CenW model simulations captured well the fluxes variations due to differences in meteorological conditions and management for the mowed paddock.