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1

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The uncertainty in simulations by a Global Biome Model (BIOME3) to alternative parameter values (2000)

Hallgren, W. S. ; Pitman, A. J

Oxford, UK : Blackwell Science Ltd

Global change biology 6 (2000), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: 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.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00325.x

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2

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Sensitivity of regional climates to localized precipitation in global models (1990)

Pitman, A. J. ; Henderson-Sellers, A. ; Yang, Z-L.

[s.l.] : Nature Publishing Group

Nature 346 (1990), S. 734-737

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] The land surface is an essential component in atmospheric general circulation models (AGCMs). A series of sensitivity experiments12 has shown that the simulation of the Earth's climate is affected by the land surface3'8 and its representation9'13. In the past decade several models for ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/346734a0

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3

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The impact of implementing the bare essentials of surface transfer land surface scheme into the BMRC GCM (1995)

Yang, Z.-L. ; Pitman, A. J. ; McAvaney, B. ; [et al.]

Springer

Climate dynamics 11 (1995), S. 279-297

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract. This study describes the first order impacts of incorporating a complex land-surface scheme, the bare essentials of surface transfer (BEST), into the Australian Bureau of Meteorology Research Centre (BMRC) global atmospheric general circulation model (GCM). Land seasonal climatologies averaged over the last six years of integrations after equilibrium from the GCM with BEST and without BEST (the control) are compared. The modeled results are evaluated with comprehensive sources of data, including the layer-cloud climatologies from the international satellite cloud climatology project (ISCCP) data from 1983 to 1991 and the surface-observed global data of Warren et al., a five-year climatology of surface albedo estimated from earth radiation budget experiment (ERBE) top-of-the-atmosphere (TOA) radiative fluxes, global grid point datasets of precipitation, and the climatological analyses of surface evaporation and albedo. Emphasis is placed on the surface evaluation of simulations of land-surface conditions such as surface roughness, surface albedo and the surface wetness factor, and on their effects on surface evaporation, precipitation, layer-cloud and surface temperature. The improvements due to the inclusion of BEST are: a realistic geographical distribution of surface roughness, a decrease in surface albedo over areas with seasonal snow cover, and an increase in surface albedo over snow-free land. The simulated reduction in surface evaporation due, in part, to the biophysical control of vegetation, is also consistent with the previous studies. Since the control climate has a dry bias, the overall simulations from the GCM with BEST are degraded, except for significant improvements for the northern winter hemisphere because of the realistic vegetation-masking effects. The implications of our results for synergistic developments of other aspects of model parameterization schemes such as boundary layer dynamics, clouds, convection and rainfall are discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820050076

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4

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Key results and implications from phase 1(c) of the Project for Intercomparison of Land-surface Parametrization Schemes (1999)

Pitman, A. J. ; Henderson-Sellers, A. ; Desborough, C. E. ; [et al.]

Springer

Climate dynamics 15 (1999), S. 673-684

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Using atmospheric forcing data generated from a general circulation climate model, sixteen land surface schemes participating in the Project for the Intercomparison of Land-surface Parametrization Schemes (PILPS) were run off-line to equilibrium using forcing data from a GCM representative of a tropical forest and a mid-latitude grassland grid point. The values for each land surface parameter (roughness length, minimum stomatal resistance, soil depth etc.) were provided. Results were quality controlled and analyzed, focusing on the scatter simulated amongst the models. There were large differences in how the models’ partitioned available energy between sensible and latent heat. Annually averaged, simulations for the tropical forest ranged by 79 1 3;W m-2 for the sensible heat flux and 80 W m-2 for the latent heat flux. For the grassland, simulations ranged by 34 W m-2 for the sensible heat flux and 27 W m-2 for the latent heat flux. Similarly large differences were found for simulated runoff and soil moisture and at the monthly time scale. The models’ simulation of annually averaged effective radiative temperature varied with a range, between all the models, of 1.4 K for tropical forest and 2.2 K for the grassland. The simulation of latent and sensible heat fluxes by a standard ‘bucket’ models was anomalous although this could be corrected by an additional resistance term. These results imply that the current land surface models do not agree on the land surface climate when the atmospheric forcing and surface parameters are prescribed. The nature of the experimental design, it being offline and with artificial forcing, generally precludes judgements concerning the relative quality of any specific model. Although these results were produced de-coupled from a host model, they do cast doubt on the reliability of land surface schemes. It is therefore a priority to resolve the disparity in the simulations, understand the reasons behind the scatter and to determine whether this lack of agreement in de-coupled tests is reproduced in coupled experiments.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820050309

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5

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Testing a GCM land surface scheme against catchment-scale runoff data (1996)

Pitman, A. J. ; Chiew, F. H. S.

Springer

Climate dynamics 12 (1996), S. 685-699

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract. A GCM land surface scheme was used, in off-line mode, to simulate the runoff, latent and sensible heat fluxes for two distinct Australian catchments using observed atmospheric forcing. The tropical Jardine River catchment is 2500 km2 and has an annual rainfall of 1700 mm y–1 while the Canning River catchment is 540 km2, has a Mediterranean climate (annual rainfall of 800 mm y–1) and is ephemeral for half the year. It was found that the standard version of a land surface scheme developed for a GCM, and initialised as for incorporation into a GCM, simulated similar latent and sensible heat fluxes compared to a basin-scale hydrological model (MODHYDROLOG) which was calibrated for each catchment. However, the standard version of the land surface scheme grossly overestimated the observed peak runoff in the wet Jardine River catchment at the expense of runoff later in the season. Increasing the soil water storage permitted the land surface scheme to simulate observed runoff quite well, but led to a different simulation of latent and sensible heat compared to MODHYDROLOG. It is concluded that this 2-layer land surface scheme was unable to simulate both catchments realistically. The land surface scheme was then extended to a three-layer model. In terms of runoff, the resulting control simulations with soil depths chosen as for the GCM were better than the best simulations obtained with the two-layer model. The three-layer model simulated similar latent and sensible heat for both catchments compared to MODHYDROLOG. Unfortunately, for the ephemeral Canning River catchment, the land surface scheme was unable to time the observed runoff peak correctly. A tentative conclusion would be that this GCM land surface scheme may be able to simulate the present day state of some larger and wetter catchments but not catchments with peaky hydrographs and zero flows for part of the year. This conclusion requires examination with a range of GCM land surface schemes against a range of catchments.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820050136

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6

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The Project for Intercomparison of Land-surface Parametrization Schemes (PILPS): 1992 to 1995 (1996)

Henderson-Sellers, A. ; McGuffie, K. ; Pitman, A. J.

Springer

Climate dynamics 12 (1996), S. 849-859

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract. The World Climate Research Programme Project for Intercomparison of Land-surface Parametrization Schemes (PILPS) is an on-going international intercomparison of land surface schemes designed for use in climate modelling and weather prediction. The five phases of PILPS are described in this work with an indication of the status of each. Phase 0 documented the status of land surface schemes. Phase 1 performed a series of off-line tests using synthetic atmospheric forcing. Phase 2 exploited observational data in off-line tests. Phase 3 was comprised of coupled tests within the Atmospheric Model Intercomparison Project (AMIP) project and finally Phase 4 will consider the performance of land-surface schemes when coupled to their host climate models in fully coupled evaluations. Results from Phase 1 indicate that there is a wide range among models. Phase 2 indicates that while some models are consistent with observations, there remains a large range among models and that many diverge greatly from observations. PILPS phases 2(a) and 2(b) results suggest that individual land-surface schemes capture specific aspects of the complex system with reasonable accuracy but no one scheme captures the whole system satisfactorily and consistently. In Phase 3 the intercomparison of PILPS schemes as a component of global atmospheric circulation models is being conducted jointly with the AMIP as diagnostic subproject number 12. Preliminary results suggest that results differ by about the same range as in the offline experiments in Phases 1 and 2. Phase 4 will couple selected land-surface schemes to the USA's National Center for Atmospheric Research climate system model and to the Australian Bureau of Meteorology limited area model.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820050147

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7

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The impact of implementing the bare essentials of surface transfer land surface scheme into the BMRC GCM (1995)

Yang, Z-L ; Pitman, A J ; McAvaney, B ; [et al.]

Springer

Climate dynamics 11 (1995), S. 279-297

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract This study describes the first order impacts of incorporating a complex land-surface scheme, the bare essentials of surface transfer (BEST), into the Australian Bureau of Meteorology Research Centre (BMRC) global atmospheric general circulation model (GCM). Land seasonal climatologies averaged over the last six years of integrations after equilibrium from the GCM with BEST and without BEST (the control) are compared. The modeled results are evaluated with comprehensive sources of data, including the layer-cloud climatologies from the international satellite cloud climatology project (ISCCP) data from 1983 to 1991 and the surface-observed global data of Warren et al., a five-year climatology of surface albedo estimated from earth radiation budget experiment (ERBE) top-of-the-atmosphere (TOA) radiatioe fluxes, global grid point datasets of precipitation, and the climatological analyses of surface evaporation and albedo. Emphasis is placed on the surface evaluation of simulations of landsurface conditions such as surface roughness, surface albedo and the surface wetness factor, and on their effects on surface evaporation, precipitation, layer-cloud and surface temperature. The improvements due to the inclusion of BEST are: a realistic geographical distribution of surface roughness, a decrease in surface albedo over areas with seasonal snow cover, and an increase in surface albedo over snow-free land. The simulated reduction in surface evaporation due, in part, to the biophysical control of vegetation, is also consistent with the previous studies. Since the control climate has a dry bias, the overall simulations from the GCM with BEST are degraded, except for significant improvements for the northern winter hemisphere because of the realistic vegetation-masking effects. The implications of our results for synergistic developments of other aspects of model parameterization schemes such as boundary layer dynamics, clouds, convection and rainfall are discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00211680

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8

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Book reviews (1990)

Reed, Richard J. ; Cortner, Hanna J. ; Morrisette, Peter M. ; [et al.]

Springer

Climatic change 16 (1990), S. 357-366

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ISSN: 1573-1480

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00144509

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9

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Sensitivity of the land surface to sub-grid scale processes: implications for climate simulations (1991)

Pitman, A. J.

Springer

Plant ecology 91 (1991), S. 121-134

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ISSN: 1573-5052

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Using a state-of-the-art land surface model in a ‘stand-alone’ mode with prescribed atmospheric forcing, a method for retaining the spatial extent and intensity of precipitation in Atmospheric General Circulation Models (AGCMs) is investigated. It is shown that the surface climatology simulated by this model is strongly dependent upon the fraction of the grid square, μ, receiving precipitation. It is also shown that fundamentally different hydrological regimes (one runoff dominated, the other evaporation dominated) are obtained for the otherwise identical situations. It is argued that the new generation of land surface models which explicitly incorporate vegetation may have to be ‘re-tuned’ if differences between large-scale and small-scale precipitation events are accommodated in AGCMs. If precipitation is always assumed to fall uniformly over the grid square, the precipitation intensity will generally be underestimated. This will lead to an overestimation of canopy interception and interception loss. Furthermore, too little precipitation will reach the soil surface, and therefore surface runoff and the soil moisture will be underestimated. With too much interception loss, and too little soil water (and soil evaporation) there will be a tendency to re-cycle precipitation back to the atmosphere too quickly, leading to the unrealistic simulation of surface-atmosphere interactions. These results, if reproduced within an AGCM, would invalidate previous simulations of the effects of changing the state of the land surface on the atmosphere.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00036052

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