The uncertainty in simulations by a Global Biome Model (BIOME3) to alternative parameter values

Abstract

Summary The sensitivity of a global biome model (BIOME3) to uncertainty in parameter values was investigated by testing the model's sensitivity to minimum and maximum parameter values obtained from an extensive literature search. Simulations were conducted replacing the default parameter value by each of the maximum and minimum values determined from the literature. In doing so, the aim was to identify those parameters where the use of an alternate (observed) value leads to a significant change in the simulation of plant functional types at a global scale, in order to identify those which are functionally important to the model. BIOME3 was found to be insensitive to changes in the majority of its parameters, providing a generally sound foundation for confidence in model simulations. However, there was considerable sensitivity shown to over a quarter of the parameters. Three main types of parameters led to a change in plant functional types distribution relative to the control simulation: (i) parameters affecting the photosynthesis parameterization; (ii) parameters affecting the evapotranspiration parameterization; and (iii) root distribution which affected both parts of the model. The main causes of sensitivity were changes in the photosynthesis parameters leading to differential changes in plant functional type's net primary productivity. This caused a shift in the competitive balance between specific plant functional types or between C3 and C4 plant types, and a consequent change in their global distribution. Changes to the evapotranspiration parameters and root distribution similarly affected net primary productivity and soil moisture, and often led to shifts in the competitive balance between grass and trees. Changes in the value for several poorly known parameters produced substantial changes in the distribution of plant functional types, and reduced the κ‐statistic to a large degree, indicating areas of potential uncertainty in the model. This suggests that great care must be taken in prescribing values to these parameters and provides guidance on which parameters need further attention in observational work.

Assessing the Response of Terrestrial Ecosystems to Potential Changes in Precipitation

“…Another limitation of current global models is the representation of the root zone depth, which varies between models but usually does not vary between biomes within a model (but see Kleidon and Heimann 1998). Root zone depth assignments can have large-scale effects on global change predictions (Hallgren and Pitman 2000).…”

Sensitivity tests of the integrated biosphere simulator to soil and vegetation characteristics in a pacific coastal coniferous forest

“…For large-scale simulations, Hallgren and Pitman (2000) also reported that the distribution of Plant Functional Types (PFTs) simulated by the BIOME3 global biome model could be very sensitive to the assumptions made concerning vertical root distribution, while Aguiar et al (1996) found that changes in vegetation composition could have major effects on mass and energy exchanges with the atmosphere. In DGVMs, this means that small uncertainties in root profile specification could lead to significant errors in simulated surface vegetation and hence in the modelled surface exchanges of energy, water and carbon.…”

“…In the present study, this competition was not simulated because Douglasfir was considered to be the only vegetation type at the site (Table 1). The global simulations of Hallgren and Pitman (2000) show a potentially important effect of root profile uncertainties on global vegetation distribution (and hence on predictions of exchanges of heat, water and carbon between surface and atmosphere) because the process of competition between lower and upper canopy species was present in their simulations. In agreement with our results, however, the simulations of Hallgren and Pitman (2000) indicated only a minor effect due to root profile uncertainties on vegetation distribution in the Canadian Pacific coastal region (Figs 3a,b in Hallgren and Pitman, 2000).…”

O conceito de bioma

“…Simulações com modelos globais da distribuição de tipos funcionais de plantas, variando os valores de certos parâmetros como fotossíntese, evapotranspiração e distribuição das raízes, provocaram modificações na produtividade primária líquida, modificações no balanço competitivo entre tipos funcionais de plantas, ou entre plantas C 3 e C 4 , com uma conseqüente modificação em sua distribuição global. Modificações em parâmetros de evapotranspiração e distribuição de raízes afetaram similarmente a produtividade primária e a umidade do solo, levando freqüentemente a modificações no balanço competitivo entre gramíneas e árvores (Hallgren & Pitman 2000). Todos estes trabalhos mostram quão delicada e susceptível são a existência e a distribuição dos seres vivos em nosso Planeta e quão graves são as modificações que nele estão ocorrendo em função das atividades humanas.…”