MULTI-OBJECTIVE CALIBRATION OF IBIS MODEL BY GENETIC ALGORITHM WITH PARAMETRIC SENSITIVITY ANALYSIS

Atmospheric circulation models combine different modules for a good description of the atmospheric dynamics. One of these modules is the representation of surface coverage, since the dynamics depends on the interaction between the atmosphere and the surface of the planet. However, these modules depend on a number of parameters that need to be adjusted. The parameter adjustment process is called model calibration. In this study, the IBIS (Integrated Biosphere Simulator) model is calibrated following a multi-objective strategy. The Pareto set, which embraces the non-dominated solutions in the search space of objective functions, is determined by a version of multi-objective genetic algorithm (NSGA-II). The model sensitivity to the parameters is evaluated by the Morris’ method. Synthetic data for calibration were obtained from the Tapajós National Forest (FloNa Tapajós), located near to the 67 km from Santarém-Cuiabá highway (2,51S, 54,58W).

Implementation of a Marauding Insect Module (MIM, version 1.0) in the Integrated BIosphere Simulator (IBIS, version 2.6b4) dynamic vegetation–land surface model

Insects defoliate and kill plants in many ecosystems worldwide. The consequences of these natural processes on terrestrial ecology and nutrient cycling are well established, and their potential climatic effects resulting from modified land–atmosphere exchanges of carbon, energy, and water are increasingly being recognized. We developed a Marauding Insect Module (MIM) to quantify, in the Integrated BIosphere Simulator (IBIS), the consequences of insect activity on biogeochemical and biogeophysical fluxes, also accounting for the effects of altered vegetation dynamics. MIM can simulate damage from three different insect functional types: (1) defoliators on broadleaf deciduous trees, (2) defoliators on needleleaf evergreen trees, and (3) bark beetles on needleleaf evergreen trees, with the resulting impacts being estimated by IBIS based on the new, insect-modified state of the vegetation. MIM further accounts for the physical presence and gradual fall of insect-killed dead standing trees. The design of MIM should facilitate the addition of other insect types besides the ones already included and could guide the development of similar modules for other process-based vegetation models. After describing IBIS–MIM, we illustrate the usefulness of the model by presenting results spanning daily to centennial timescales for vegetation dynamics and cycling of carbon, energy, and water in a simplified setting and for bark beetles only. More precisely, we simulated 100 % mortality events from the mountain pine beetle for three locations in western Canada. We then show that these simulated impacts agree with many previous studies based on field measurements, satellite data, or modelling. MIM and similar tools should therefore be of great value in assessing the wide array of impacts resulting from insect-induced plant damage in the Earth system.

Implementation of a Marauding Insect Module (MIM, version 1.0) in the Integrated BIosphere Simulator (IBIS, version 2.6b4) Dynamic Vegetation–Land Surface Model

Insects defoliate and kill plants in many ecosystems worldwide. The consequences of these natural processes on terrestrial ecology and nutrient cycling are well established, and their potential climatic effects resulting from modified land–atmosphere exchanges of carbon, energy, and water are increasingly being recognized. We developed a Marauding Insect Module (MIM) to quantify, in the Integrated BIosphere Simulator (IBIS), the consequences of insect activity on biogeochemical and biogeophysical fluxes, also accounting for the effects of altered vegetation dynamics. MIM can simulate damage from broadleaf defoliators, needleleaf defoliators, and bark beetles, with the resulting impacts being estimated by IBIS based on the new, insect-modified state of the vegetation. MIM further accounts for the physical presence and gradual fall of insect-killed dead standing trees. The design of MIM should facilitate the addition of other insect types besides the ones already included and could guide the development of similar modules for other process-based vegetation models. After describing IBIS-MIM, we illustrate the usefulness of the model by presenting results spanning daily to centennial timescales for vegetation dynamics and cycling of carbon, energy, and water following a simulated outbreak of the mountain pine beetle. We then show that these simulated impacts agree with many previous studies based on field measurements, satellite data, or modelling. MIM and similar tools should therefore be of great value in assessing the wide array of impacts resulting from insect-induced plant damage in the Earth system.

Calibration and Validation of the Integrated Biosphere Simulator (IBIS) for a Brazilian Semiarid Region

The reliability of predictions from climate and weather models is linked to an adequate representation of the land surface processes. To evaluate performance and to improve predictions, land surface models are calibrated against observed data. Despite an extensive literature describing methods of land surface model calibration, few studies have applied a calibration method for semiarid natural vegetation, especially for the semiarid northeast of Brazil, which presents caatinga as its natural vegetation. Caatinga is a highly dynamic ecosystem with the physics at the land surface–atmosphere interface still poorly understood. Therefore, in this study a multiobjective hierarchical method, which provides means to estimate optimal values of the model parameters through calibration, is evaluated. This method is applied to caatinga by using the Integrated Biosphere Simulator (IBIS). Results demonstrated that the calibrated set of vegetation parameters produced a considerably different energy balance from the default parameters. In general, the model was able to simulate the partition of the available energy into sensible and latent heat fluxes when the calibrated parameters were used. The IBIS model was not able to capture short-term, intense changes in latent heat flux from a dry condition to a wetter condition, however, even when the new set of calibrated parameters was used. Therefore, the parameter optimization may not be sufficient if processes are missing or misrepresented. This study is one of the first to understand the physics at the land surface–atmosphere interface in the caatinga ecosystem and to evaluate the ability of the IBIS model to represent the biophysical interactions in this important ecosystem.

Impactos das mudanças de cobertura vegetal nos processos de superfície na região semiárida do Brasil

A cobertura vegetal da superfície continental tem sido consideravelmente alterada pelas atividades humanas, principalmente através da conversão em grande escala da vegetação natural por áreas de cultivos e pastagens. Essas mudanças na cobertura da superfície podem alterar o clima regional e global por meio de processos biofísicos e biogeoquímicos. Assim, o presente trabalho avaliou como a substituição da vegetação natural da caatinga por agropecuária, bem como a degradação da caatinga, podem causar modificações nos processos de superfície na região semiárida do Nordeste do Brasil (NEB), a qual é uma das mais vulneráveis do Brasil, do ponto de vista social, à mudança de clima. Para isto, foram realizados experimentos numéricos de conversão da cobertura da superfície utilizando-se o modelo Integrated Biosphere Simulator - IBIS. Por meio da conversão da cobertura vegetal, as características morfológicas e biofísicas da vegetação foram modificadas e por isso, causaram alterações nas componentes dos balanços de energia, de água e de carbono. O balanço de energia foi mais afetado pelo aumento do albedo decorrente da alteração da vegetação caatinga para agropecuária e para caatinga degradada. Além disso, as alterações do comprimento de rugosidade e das propriedades estomáticas da vegetação corroboraram para as alterações ocorridas nas trocas turbulentas entre a superfície e a atmosfera. Com relação às componentes do balanço de carbono, durante a estação chuvosa com a conversão da caatinga natural para agropecuária, houve um aumento da assimilação de CO2 (NEE) e com isso maior Produtividade Primária Líquida do ecossistema (NPP). O contrário ocorreu com a conversão para caatinga degradada, na qual a assimilação se manteve próxima de zero durante as horas do dia e NPP foi reduzida, o que pode ter ocorrido em função das alterações ocorridas no Índice de Área Foliar (IAF), tanto para a agropecuária, como para a caatinga degradada.

THE INFLUENCE OF ARCHITECTURAL AND SPECTRAL PARAMETERS OF A TROPICAL FOREST CANOPY UNDER ITS REFLECTANCE DESCRIBED BY IBIS MODEL

Estudar e monitorar a cobertura vegetal são importantes para compreender o padrão climático atual em escala regional e global. Os Modelos de Dinâmica de Vegetação (MDV) são ferramentas úteis nos estudos de determinado bioma, pois são baseados em princípios físicos e em condições iniciais e de contorno, podendo então obter indícios dos fatores que influenciam o ambiente modelado, fazer previsões futuras do comportamento da vegetação e, associados a outros modelos, fazer previsões futuras da influência da vegetação no clima, ou da mudança do clima na vegetação. Em particular, os modelos que simulam a reflectância de um dossel fazem parte dos MDV. Alguns estudos têm sido feitos para identificar a influência dos componentes do dossel sobre o albedo da cobertura vegetal, obtendo a melhor configuração dos parâmetros a serem usados. Para a vegetação, importantes parâmetros são estimados a partir da reflectância em faixas espectrais específicas. Nesse aspecto o objetivo desse trabalho foi adicionar no modelo IBIS – Integrated Biosphere Simulator três bandas vermelho, infravermelho próximo e azul, referentes às bandas 1, 2 e 3 do sensor MODIS, a bordo dos satélites TERRA e AQUA, observando a sensibilidade aos parâmetros ópticos (reflectância de folhas) e arquitetônicos (inclinação das folhas) do dossel e calibrando esses parâmetros de acordo com os produtos de reflectância de superfície e índice de vegetação do MODIS para a Reservado Cuieiras (K34). A análise de sensibilidade indicou forte influência dos parâmetros referentes à parte superior do dossel. A combinação dos parâmetros que minimizou o RMSE do EVI – Enhanced Vegetation Index (RMSEmin =0,0245) foi a inclinação das folhas do dossel superior χup =0,92, reflectância das folhas da parte superior do dossel na faixa do azul ρblue−up = 0,0162, vermelho ρred−up = 0,0466 e infravermelho próximo ρnir−up = 0,4427. ABSTRACT: Studying and monitoring vegetation is the key to understand the current climate pattern in both regional and global scales. Dynamical Vegetation Models(DVM) are useful tools in biome studies, since they are based on physical principles as well as on initial and boundary conditions. They are able to obtain evidences of factors that influence the modeled environment, predicting future vegetation behavior and, in association with other models, making future predictions of vegetation influence on climate or the effect of climate change on vegetation it self. In particular, reflectance models are part of DVMs. Some studies have attempted to identify canopy elements influence on the vegetation cover albedo, obtaining the best configuration of parameters to be used. Important parameters are estimated from the reflectance inspecific spectral bands. Thus, the objective of this study was to evaluate the IBIS model - Integrated Biosphere Simulator performance running it at three bands – red, near infrared, and blue, corresponding to the bands 1, 2 and 3 of the MODIS sensor, onboard of the TERRA and AQUA satellites. The sensitivity to optical parameters (leaf reflectance) and architecture (slope of the leaves) of the canopy was also evaluated. These optical and architectural parameters were calibrated according to the surface reflectance and vegetation index from MODIS for the Cuieiras Reserve (K34). The sensitivity analysis indicated a strong influence of the upper canopy parameters.The parameters combination that minimizes the RMSE of EVI – Enhanced Vegetation Index (RMSE = 0.0245) were the slope of the upper canopy leaves χup = 0.92,reflectance from the upper canopy leaves in the blue band ρblue−up = 0.0162, red band ρred−up = 0.0466 and near infrared band ρnir−up = 0.4427.Keywords: reflectance models, tropical rainforest, remote sensing

Modeling radiative transfer in tropical rainforest canopies: sensitivity of simulated albedo to canopy architectural and optical parameters

This study evaluates the sensitivity of the surface albedo simulated by the Integrated Biosphere Simulator (IBIS) to a set of Amazonian tropical rainforest canopy architectural and optical parameters. The parameters tested in this study are the orientation and reflectance of the leaves of upper and lower canopies in the visible (VIS) and near-infrared (NIR) spectral bands. The results are evaluated against albedo measurements taken above the K34 site at the INPA (Instituto Nacional de Pesquisas da Amazônia) Cuieiras Biological Reserve. The sensitivity analysis indicates a strong response to the upper canopy leaves orientation (x up) and to the reflectivity in the near-infrared spectral band (rNIR,up), a smaller sensitivity to the reflectivity in the visible spectral band (rVIS,up) and no sensitivity at all to the lower canopy parameters, which is consistent with the canopy structure. The combination of parameters that minimized the Root Mean Square Error and mean relative error are Xup = 0.86, rVIS,up = 0.062 and rNIR,up = 0.275. The parameterizations performed resulted in successful simulations of tropical rainforest albedo by IBIS, indicating its potential to simulate the canopy radiative transfer for narrow spectral bands and permitting close comparison with remote sensing products.

Coupling of Integrated Biosphere Simulator to Regional Climate Model Version 3

A description of the coupling of Integrated Biosphere Simulator (IBIS) to Regional Climate Model version 3 (RegCM3) is presented. IBIS introduces several key advantages to RegCM3, most notably vegetation dynamics, the coexistence of multiple plant functional types in the same grid cell, more sophisticated plant phenology, plant competition, explicit modeling of soil/plant biogeochemistry, and additional soil and snow layers. A single subroutine was created that allows RegCM3 to use IBIS for surface physics calculations. A revised initialization scheme was implemented for RegCM3–IBIS, including an IBIS-specific prescription of vegetation and soil properties. To illustrate the relative strengths and weaknesses of RegCM3–IBIS, one 4-yr numerical experiment was completed to assess ability of both RegCM3–IBIS (with static vegetation) and RegCM3 with its native land surface model, Biosphere–Atmosphere Transfer Scheme 1e (RegCM3–BATS1e), to simulate the energy and water budgets. Each model was evaluated using the NASA Surface Radiation Budget, FLUXNET micrometeorological tower observations, and Climate Research Unit Time Series 2.0. RegCM3–IBIS and RegCM3–BATS1e simulate excess shortwave radiation incident and absorbed at the surface, especially during the summer months. RegCM3–IBIS limits evapotranspiration, which allows for the correct estimation of latent heat flux, but increases surface temperature, sensible heat flux, and net longwave radiation. RegCM3–BATS1e better simulates temperature, net longwave radiation, and sensible heat flux, but systematically overestimates latent heat flux. This objective comparison of two different land surface models will help guide future adjustments to surface physics schemes within RegCM3.