How can social–ecological system models simulate the emergence of social–ecological crises?

The idea that human impacts on natural systems might trigger large‐scale, social–ecological ‘crises’ or ‘breakdowns’ is attracting increasing scientific, societal and political attention, but the risks of such crises remain hard to assess or ameliorate. Social–ecological systems have complex dynamics, with bifurcations, nonlinearities and tipping points all emerging from the interaction of multiple human and natural processes. Computational modelling is a key tool in understanding these processes and their effects on system resilience. However, models that operate over large geographical extents often rely on assumptions such as economic equilibrium and optimisation in social–economic systems, and mean‐field or trend‐based behaviour in ecological systems, which limit the simulation of crisis dynamics. Alternative forms of modelling focus on simulating local‐scale processes that underpin the dynamics of social–ecological systems. Recent improvements in data resources and computational tools mean that such modelling is now technically feasible across large geographical extents. We consider the contributions that the different types of model can make to simulating social–ecological crises. While no models are able to predict exact outcomes in complex social–ecological systems, we suggest that one new approach with substantial promise is hybrid modelling that uses existing model architectures to isolate and understand key processes, revealing risks and associated uncertainties of crises emerging. We outline convergent and efficient functional descriptions of social and ecological systems that can be used to develop such models, data resources that can support them, and possible ‘high‐level’ processes that they can represent

Three-dimensional Keplerian orbit-superposition models of the nucleus of M31

We present three-dimensional eccentric disc models of the nucleus of M31, modelling the disc as a linear combination of thick rings of massless stars orbiting in the potential of a central black hole. Our models are nonparametric generalisations of the parametric models of Peiris & Tremaine. The models reproduce well the observed WFPC2 photometry, the detailed line-of-sight velocity distributions from STIS observations along P1 and P2, together with the qualitative features of the OASIS kinematic maps. We confirm Peiris & Tremaine's finding that nuclear discs aligned with the larger disc of M31 are strongly ruled out. Our optimal model is inclined at 57 degrees with respect to the line of sight of M31 and has a position angle of 55 degrees. It has a central black hole of mass 10^8 solar masses, and, when viewed in three dimensions, shows a clear enhancement in the density of stars around the black hole. The distribution of orbit eccentricities in our models is similar to Peiris & Tremaine's model, but we find significantly different inclination distributions, which might provide valuable clues to the origin of the disc.Comment: 13 pages, 14 figures. MNRAS, in pres

How modelling paradigms affect simulated future land use change

Land use models operating at regional to global scales are almost exclusively based on the single paradigm of economic optimisation. Models based on different paradigms are known to produce very different results, but these are not always equivalent or attributable to particular assumptions. In this study, we compare two pan-European integrated land use models that utilise the same climatic and socio-economic scenarios but which adopt fundamentally different modelling paradigms. One of these is a constrained optimising economic-equilibrium model, and the other is a stochastic agent-based model. We run both models for a range of scenario combinations and compare their projections of spatially aggregate and disaggregate land use changes and ecosystem service supply levels in food, forest and associated environmental systems. We find that the models produce very different results in some scenarios, with simulated food production varying by up to half of total demand and the extent of intensive agriculture varying by up to 25 % of the EU land area. The agent-based model projects more multifunctional and heterogeneous landscapes in most scenarios, providing a wider range of ecosystem services at landscape scales, as agents make individual, time-dependent decisions that reflect economic and non-economic motivations. This tendency also results in food shortages under certain scenario conditions. The optimisation model, in contrast, maintains food supply through intensification of agricultural production in the most profitable areas, sometimes at the expense of land abandonment in large parts of Europe. We relate the principal differences observed to underlying model assumptions and hypothesise that optimisation may be appropriate in scenarios that allow for coherent political and economic control of land systems, but not in scenarios in which economic and other scenario conditions prevent the changes in prices and responses required to approach economic equilibrium. In these circumstances, agent-based modelling allows explicit consideration of behavioural processes, but in doing so it provides a highly flexible account of land system development that is harder to link to underlying assumptions. We suggest that structured comparisons of parallel and transparent but paradigmatically distinct models are an important method for better understanding the potential scope and uncertainties of future land use change, particularly given the substantive differences that currently exist in the outcomes of such models

Evaluation and Calibration of an Agent Based Land use Model Using Remotely Sensed Land Cover and Primary Productivity Data

Identifying and reducing uncertainties in future land use projections are becoming critical in integrated assessments of the climate and social change scenarios. Here, we quantified correspondence between remotely sensed land cover and a model-derived projection of European land use to build a calibration and evaluation framework for land use projection models. For an eight-year period (2006–2013), we compared simulated land uses from a model (CRAFTY-EU), defined as agent functional types, against remotely sensed MODIS land cover. Information between two datasets and spatial complexity are calculated, which allowed the evaluation of the CRAFTY model and calibration of the model parameters. The computational cost was high. Thus more efficient searching algorithms are called for. The evaluation framework holds promise for better calibration of land use decision models to increase model usability and improve the value of future land cover projections

Relative importance of deterministic and stochastic processes for beta diversity of bird assemblages in Yunnan, China

Evaluating the relative importance of deterministic and stochastic processes underlying taxonomic and functional beta diversity is crucial in community ecology, because it can reveal the dominant processes of community assembly. However, studies of bird communities remain rare and of limited spatial extents. In this study, we described the taxonomic and functional beta diversity patterns of 32 passerine bird assemblages of Yunnan Province, China. We constructed null models based on observed species beta diversity and used multiple regressions on distance matrices to evaluate the relative contributions of deterministic and stochastic processes to passerine bird assemblage dissimilarity. Our results showed significant geographic distance decay in taxonomic and functional similarity, with passerine bird assemblages located in the northwest and southwest of the province having higher functional beta diversity values than expected. Environmental distance and geographic distance explained a similar amount taxonomic beta diversity, but environmental distance explained much more functional beta diversity. Our results suggest that both deterministic and stochastic processes drive taxonomic beta diversity, but that deterministic processes, particularly environmental filtering, play a dominant role in driving functional beta diversity of passerine bird assemblages at sub-national scale

Assessing the quality of land system models: moving from valibration to evaludation

Reviews suggest that evaluation of land system models is largely inadequate, with undue reliance on a vague concept of validation. Efforts to improve and standardise evaluation practices have so far had limited effect. In this article we examine the issues surrounding land system model evaluation and consider the relevance of the TRACE framework for environmental model documentation. In doing so, we discuss the application of a comprehensive range of evaluation procedures to existing models, and the value of each specific procedure. We develop a tiered checklist for going beyond what seems to be a common practice of ‘valibration’ (the repeated variation of model parameter values to achieve agreement with data) to achieving ‘evaludation’ (the rigorous, broad-based assessment of model quality and validity). We propose the Land Use Change – TRACE (LUC-TRACE) model evaludation protocol and argue that engagement with a comprehensive protocol of this kind (even if not this particular one) is valuable in ensuring that land system model results are interpreted appropriately. We also suggest that the main benefit of such formalised structures is to assist the process of critical thinking about model utility, and that the variety of legitimate modelling approaches precludes universal tests of whether a model is ‘valid’. Evaludation is therefore a detailed and subjective process requiring the sustained intellectual engagement of model developers and users

The metabolism of living space:allometric scaling of energy use in UK domestic buildings

Understanding and reducing domestic energy usage is seen as key to achieving national greenhouse gas emission targets, as well ensuring sustainable consumption at a domestic level. Domestic buildings represent a well-defined unit of space with numerous, easily measurable characteristics. They can also be perceived as being the terminal, end-use elements of a global resource distribution network, as defined by Jarvis et al., (2015). Such networks have drawn comparisons to biological organisms in how they acquire, transform, use and dispose of resources from their surrounding environment through a metabolic system of processing. This thesis aims to more deeply understand interrelations between, people, energy and space at a domestic level, assessing the influence of building geometry and social practices on scaling relationships relating to domestic energy consumption. Scaling relationships relating to the physical building properties have been studied extensively, however none directly assess how total energy usage scales across the domestic building stock. Data is abstracted form the 2012 English Housing Survey (EHS) housing stock dataset, which contains physical and demographic data relating to ~14k randomly sampled households across England. Scaling relationships are established between household size and total energy usage, both across the entire housing stock and by selected building characteristics, revealing scaling effects pertaining to specific domestic properties. Across the entire housing stock, a scaling exponent of 0.8032 ± 0.013 is observed for the relationship between household total floor area and total energy consumption, indicating a decrease in energy use per unit space with increased household size. This result is set within a context of building geometric properties and theories of societal metabolism, drawing extensively on current literature and this researches own findings. Understanding the origins of such scaling could potentially hold important implications for how individuals perceive their energy consumption, both in relation to physical domestic buildings and wider society