Tom Veldkamp: Advances in Land Models

As I mentioned before, the Global Land Project website is experimenting with the use of webcasts to enable the wider network to “participate” and use the GLP webpage as a resource. For example, several presentations are available for viewing from the Third Land System Science (LaSyS) Workshop entitled ‘Handling complex series of natural and socio-economic processes’ and held in Denmark in October of 2007. One that caught my attention was by Tom Veldkamp, mainly because of its succinct title: Advances in Land Models [webcast works best in IE].


Presented in the context of other CHANS research, Veldkamp used an example from the south of Spain to discuss recent modelling approaches to examine the effects of human decisions on environmental processes and the feedbacks between human and natural systems. The Spanish example examined the interaction of human land-use decision making and soil erosion. A multi-scale erosion model, LAPSUS, represented the interactive natural and human processes occurring olive groves on steep hillslopes; gullying caused by extreme rainfall events and attempts to preserve soils and remove gullies by ploughing. Monte Carlo simulations were used to explore uncertainties in model results and highlighted the importance of path dependencies. As such, another example of the historical dimension of ‘open’ systems and the difficulties it presents for environmental modellers.

The LAPSUS model was coupled with the well known land use/cover change CLUE model to examine feedbacks between human land use and erosion. The coupled model was used to examine the potential implications of farmers adopting land use practices as a response to erosion. Interestingly, the model suggested that human adaptation strategy modelled would not lead to reduced erosion.

Veldkamp also discusses the issue of validating simulation models of self-organising processes, and suggests that ensemble and scenario approaches such as those used in global climate modelling are necessary for this class of models. However, rather than simply using ‘static’ scenarios that specify model boundary conditions, such as the IPCC SRES scenarios, scenarios that represent some form of feedback with the model itself will be more useful. Again, this comes back to his point about the importance of representing feedbacks in coupled human and natural systems.

For example, Veldkamp suggests the use of “Fuzzy Cognitive Maps” to generate ‘dynamic’ scenarios. Essentially, these fuzzy cognitive maps are produced by asking local stakeholders in the systems under study to quantify the effects of the different factors driving change. First, the appropriate components of the system are identified. Next, the feedbacks between these components are identified. Finally, the stakeholders are asked to estimate how strong these feedbacks are (on a scale of zero to one). This results in a semi-quantitative systems model that can be run for several iterations to examine the consequences of the feedbacks within the system. This method is still in development and Veldkamp highlighted several pros and cons:

Pros:

  • it is relatively easy and quick to do
  • it forces the stakeholders to be explicit
  • the emphasis is placed on the feedbacks within the system

Cons:

  • it is a semi-quantitative approach
  • often feedbacks are of incomparable units of measurement
  • time is ill defined
  • stakeholders are often more concerned with the exact values they put on an interaction rather than the relative importance of the feedbacks

I agree when Veldkamp suggests this ‘fuzzy cognitive mapping’ is a promising approach to scenario development and incorporation into simulation modelling. Indeed, during my PhD research I explored the use of an agent-based model of land use decision-making to provide scenarios of land use/cover change for a model of forest succession-disturbance dynamics (and which I am currently writing up for publication). ‘Dynamic’ model scenario approaches show real promise for representing feedbacks in coupled human natural systems. As Veldkamp concludes, these feedbacks, along with the non-linearities in system behaviour they produce, need to be explicitly represented and explored to improve our understanding of the interactions between humans and their environment.

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