1. Comparing Simulated and Observed Gross Primary Productivity
Schaefer, Kevin1, NACP Site Synthesis Participants2
1 National Snow and Ice Data Center, University of Colorado
2NACP Site-Level Interim Synthesis
Contact: Kevin Schaefer: ;
1) Objective
3) Taylor Plot Daily GPP
5) Light Use Efficiency
Figure 5: Typical simulated and observed Light Use Efficiency (LUE) curves. On average, the model LUE slopes are too small. Model performance would improve with better values for parameters that define LUE slope, such as the leaf-to-canopy-scaling factor or Vmax.
Compare simulated and observed Gross Primary Productivity (GPP)
Identify how to improve models
Daily Ave. SW Radiation (W m-2)
GPP (mmol m-2 s-1)
Observed
Simulated
US-Ho1
US-Ha1 C5
C5.1
Standard Deviation Ratio
Figure 3: Taylor diagram for all sites based on daily average GPP. The radial direction is essentially the ratio of simulated to observed GPP. Some models overestimate GPP, but on average, models underestimate GPP
2) NACP Site Synthesis
The Site Synthesis compares simulated and observed fluxes at eddy covariance flux towers across North America. Models were spun up to steady state using gap-filled observed weather. Observed fluxes were filtered, filled, and partitioned in GPP and respiration. Total uncertainty includes random, U* filtering, gap-filling, and partitioning uncertainty.
4) Monthly GPP
6) Temperature Response
Date (Year)
GPP (mmol m-2 s-1)
Observed
Simulated
US-Ho1
US-Ha1
Figure 6: Typical simulated and observed temperature response curves. Models overestimate GPP at low temperatures and underestimate GPP at high temperatures. Model performance would improve with better values for parameters controlling temperature response, such as optimal temperature.
Daily Average Temperature (°C)
GPP (mmol m-2 s-1)
Observed
Simulated
US-Ho1
US-Ha1
Figure 4: Typical plots of observed and simulated monthly average GPP. On average, models underestimate GPP, with simulated seasonal amplitudes between % of observed values.
Figure 1: Eddy covariance flux tower sites participating in the NACP Site Synthesis. Sites in this analysis are the red and blue triangles.
Figure 2: Table listing the models participating in this analysis. The models include three variants of MODIS GPP, the mean of all models, and the mean of those models that resolve the diurnal cycle.
7) Conclusions
1) Models underestimate GPP
2) Need better values for LUE and Temperature Response parameters