NEPIP - Modeling

## Modeling

Modeling has been a central element of U.S. GLOBEC programs for a variety of reasons. Foremost, is the fact that by its very nature, the fundamental goal of U.S. GLOBEC--to predict the effects of future climate change--requires a predictive model. Models are the means of understanding complex interactions and projecting this understanding into the future for use in, for example, fisheries recruitment prediction. The Northeast Pacific program will generate information and understanding from a variety of disciplines (e.g., biology, physical oceanography, atmospheric sciences), a range of temporal and spatial scales, and several levels of biological organization (i.e, individual bioenergetics, population dynamics, food web interactions). Models will be required to integrate these so that the information can be used to project the consequences of likely climate change. To do this, we need models that span the range from the scale of basin-wide and decadal changes such as regime shifts to the scale of individual diel planktonic movement over meters. Modeling studies will be closely coordinated with monitoring, retrospective analysis and process studies. Building on the experience on Georges Bank, the large-scale modeling will be one of the first activities of the program. This early start is important to capture climate scale variability, set the boundary conditions for regional-scale models and the process studies, and recommend representative monitoring tactics.

In addition, models in this program will function as essential elements of the scientific efforts. Here too, they will serve to integrate various types of information, but the goals will be different. They will be used to test hypotheses, to determine sensitivities, to plan research, and to evaluate the results of interdisciplinary research.

To meet the general goals of the U.S. GLOBEC Northeast Pacific program, the models can focus on the broadest suite of species and issues relevant to the effects of climate change on North Pacific coastal ecosystems. Modeling studies may be developed with a focus on species targeted for the process studies (Table 3) or other non-targeted species, which could be sampled in the monitoring or analyzed in retrospective studies (Table 4).

Development of models well in advance of any field investigations has been an explicit goal of the U.S. GLOBEC program. An earlier U.S. GLOBEC workshop on secondary production modeling identified five general issues which are critical to predictive modeling that couples physical and biological processes (U.S. GLOBEC 1995).

- The role of organism motility (independent of the fluid medium), especially for the higher trophic level populations on which GLOBEC focuses. Several of the target organisms are more than passive floaters--they make choices such as vertical migration, swarming, etc.--and this has implications for transport, retention in favorable habitats, growth and survival.

- Differences in trophic organization--for example, food webs with gelatinous zooplankton as top predators, compared to those with carnivores, like salmon, at the highest trophic level.

- The coupling of processes acting at different spatial and temporal scales, as well as different levels of organization. An ultimate goal is the development of large- or basin-scale models that are coupled to more-detailed regional-scale biophysical models, and are capable of forecasting effects of climate changes on the zooplankton and fish populations.

- The incorporation of data into models, and the converse activity of utilizing model results to plan and to interpret field and laboratory studies.

- The availability of coupled biological-physical models to the larger community, and a broad-based community modeling effort with an enduring funding commitment.

Planning activities for the Northeast Pacific program (U.S. GLOBEC Report No. 11, 1994; and U.S. GLOBEC Report No. 15, 1996) have identified four specific modeling efforts that are needed to address these general issues.

- Basin-scale general circulation modeling with higher-resolution, nested coastal biological-physical components. A link to entire North Pacific simulations that are coupled to large scale atmospheric models would be desirable, especially for hindcasting studies.

- Regional-scale coupled biological-physical models. The best of these endeavors would aim to assimilate available observations (e.g., remote sensing data, buoy data, etc.), resolving the exchange of water and organisms between the coastal shelf and deeper oceanic waters.

- Coupled (mesoscale) biological-physical formulations. Models of this type should aim to resolve fronts, include mixed-layer dynamics, possibly address the shallow, turbulent inner shelf, and operate over diurnal time scales. They might address the separation of the upwelling front from the coast, including the relative roles of topographic irregularities and wind forcing. They should incorporate coastal transport processes and detailed biology, including food web relations and organism behavior.

- Modeling efforts that investigate the response of biological metapopulations to spatially and temporally varying physical forcing (Botsford et al. 1994). Some attention should be paid to models with very detailed biology, and less detailed physical transport. Examples might include bioenergetic models of juvenile salmon, predator relations, seasonal prey switching behavior, and/or nearshore food web dynamics for several different environmental scenarios. Some of these issues might best be addressed by individual-based models.

Several necessary lines of investigation cut across these model types. For example, the functional details of how to parameterize individual interactions between organisms (e.g., predator-prey) is a challenge to modelers at all scales. Moreover, how one might embed a regional model of coupled biological-physical processes within a basin-scale circulation model, or a mesoscale formulation within a regional model, remains a challenge. Technical concerns, like the specification of boundary conditions, particularly along open boundary segments, are far from settled at any scale. The assimilation of biological data into models of all kinds is another unsolved (and barely addressed) problem. Finally, models need to be verified, for it is only verified models that are of ultimate use.

A significant constraint on future progress is the lack of reliable and generally accepted coupled models available to the research community at large. Few users can be found even for those models for which some level of reliability can be claimed. To remedy this situation will demand resources for community model development and testing, and a commitment to the user communities. Rapid response to these widely acknowledged needs would allow the broader community to take advantage of opportunities represented by recent improvements in computer architectures, high-speed networking capabilities, and hierarchical data management and retrieval systems.