Boreal forest CO₂ exchange and evapotranspiration predicted by nine ecosystem process models: Intermodel comparisons and relationships to field measurements

Abstract

Abstract. Nine ecosystem process models were used to predict CO2 and water vapor exchanges by a 150-year-old black spruce forest in central Canada during 1994-1996 to evaluate and improve the models. Three models had hourly time steps, five had daily time steps, and one had monthly time steps. Model input included site ecosystem characteristics and meteorology. Model predictions were compared to eddy covariance (EC) measurements of whole-ecosystem CO2 exchange and evapotranspiration, to chamber measurements of nighttime moss-surface CO2 release, and to ground-based estimates of annual gross primary production, net primary production, net ecosystem production (NEP), plant respiration, and decomposition. Model-model differences were apparent for all variables. Model-measurement agreement was good in some cases but poor in others.Modeled annual NEP ranged from -11 g C m -2 (weak CO 2 source) to 85 g C m -2 (moderate CO2 sink). The models generally predicted greater annual CO2 sink activity than measured by EC, a discrepancy consistent with the fact that model parameterizations represented the more productive fraction of the EC tower "footprint." At hourly to monthly timescales, predictions bracketed EC measurements so median predictions were similar to measurements, but there were quantitatively important model-measurement discrepancies found for all models at subannual timescales. For these models and input data, hourly time steps (and greater complexity) compared to daily time steps tended to improve model-measurement agreement for daily scale CO 2 exchange and evapotranspiration (as judged by root-mean-squared error). Model time step and complexity played only small roles in monthly to annual predictions. IntroductionThe boreal forest biome is estimated to cover 6-13% of

Evaluating the Community Land Model in a pine stand with shading manipulations and <sup>13</sup>CO<sub>2</sub> labeling

“…CLM has been evaluated against observations from a wide range of sources, and these evaluations have resulted in improved model performance (Bauerle et al, 2012;Bonan et al, 2011Bonan et al, , 2012Koven et al, 2013;Lawrence et al, 2011;Mao et al, 2012aMao et al, , b, 2013Oleson et al, 2008;Randerson et al, 2009;Riley et al, 2011;Shi et al, 2011Shi et al, , 2013Shi et al, , 2015Thornton et al, 2007). Nevertheless, little attention has been paid to CLM's ability to replicate short-term manipulative experiments, which provide an avenue for exploring and validating model response to sudden, large changes in environmental drivers that control physiological and ecological responses (Amthor et al, 2001;Bonan et al, 2013;Shi et al, 2015). Processes operating over short timescales can have long-lived ecosystem consequences through indirect effects; e.g., stomatal conductance varies on timescales of hours or shorter, but indirect effects on site-level water balance through controls on transpiration can extend to annual timescales and beyond.…”

Carbon and energy fluxes in cropland ecosystems: a model-data comparison

“…Previous model comparison studies mostly focused on forested (e.g. Ryan et al 1996;Amthor et al 2001;Grant et al 2005), and agricultural (e.g. Semenov et al 1996;Frolking et al 1998;Ciais et al 2010;Asseng et al 2013Asseng et al , 2015Bassu et al 2014;Martre et al 2015) ecosystems.…”

Spatial and seasonal variations in evapotranspiration over Canada's landmass

“…1) that are dynamically coupled with each other to simulate the land surface: (i) radiation transfer Wang et al, 2007), (ii) energy balance (Wang et al, 2002a;Zhang et al, 2008), (iii) water dynamics including surface watergroundwater interactions (Wang, 2008(Wang, , 2012Wang et al, 2009a, b), and (iv) carbon and (v) nitrogen biogeochemical cycles (Wang et al, , 2002b. EALCO has been calibrated and validated throughout using tower-flux measurements and watershed-level water budget approach, which were reported in the above literature as well as in Amthor et al (2001), Potter et al (2001), Hanson et al (2004), Grant et al (2005Grant et al ( , 2006, Fernandes et al (2007), Mi et al (2007Mi et al ( , 2009, Li et al (2011), Widlowski et al (2011), and Yang et al (2012. In this study, we report the large-scale characterization of ET by EALCO across Canada's landmass and validation by comparing with other existing studies.…”