ISSN:0277-6693    

DOI:10.1002/for.3980100102

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractA context and introduction are provided for nine contributed articles on Forecasting Environmental Change. Since the first quantitative studies of the ‘predicament of mankind’ at the end of the 1960s, large‐scale forecasting models have attracted substantial criticism on the grounds of failing both to inform the policy process and to embrace the notion of surprise‐rich futures. Almost all attempts at developing models of environmental systems, at whatever scale, have been dogged by the sceptic's question: Is the model capable of predicting conditions substantially different from those observed in the past? The question, strictly speaking, is not answerable. The paper defines therefore three approaches to the development of modelsthe mechanical, metric, and linguistic paradigmsand constructs thence a reorientation of the customary problem of prediction in order to explore the concept of reachable, and radically different, futures. Such reorientation depends crucially on a juxtaposition of the linguistic and mechanical descriptions of a system's behaviour. The nine papers of this special issue are then summarized in the context provided by this reconsideration of how we formalize our thinking about the behaviour of systems, and of what might be meant by the systematic analysis of reachable

ISSN:0277-6693    

DOI:10.1002/for.3980100103

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractLong‐range weather forecasting is a notoriously difficult area of environmental science. However, recent improved understanding of atmospheric dynamics and better observations indicate that useful progress, rooted in scientifically sound ideas, may be possible with long‐range forecasting in the tropics. We describe recent research into the mechanisms and prediction of rainfall in the sub‐Sahara during the main summer rainfall season, concentrating on the Sahel region. We use a complex physical model of the atmosphere (a ‘general circulation’ model) and two relatively simple statistical models to show that large‐scale variations in sea surface temperature (SST) can strongly influence seasonal Sahel rainfall. Persistence of patterns of SST anomalies (deviations from long‐term average) is sufficient to allow useful forecasting techniques to be based on fields of SST anomalies observed in the preceding spring. However, persistence of the SST anomalies may not always be sufficient to provide a ski

ISSN:0277-6693    

DOI:10.1002/for.3980100104

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe paper presents a unified, fully recursive approach to the modelling, forecasting and seasonal adjustment of non‐stationary time series and shows how it can be used as a flexible tool in the analysis of environmental data. The approach is based on time‐variable parameter (TVP) versions of various well‐known time‐series models and exploits the suite of novel, recursive filtering and fixed interval smoothing algorithms available in themicroCAPTAIN computer program. The practical utility of the analysis is demonstrated by an example based on the analysis of atmospheric CO2and sea surface temperature anoma

ISSN:0277-6693    

DOI:10.1002/for.3980100105

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractNumerical models have been widely used in risk studies to estimate how hypothetical releases of radionuclides will disperse and lead to exposure of the population. In this context large numbers of possible scenarios are treated; absolute accuracy in simulating each particular situation is not necessary as long as the correct statistical distribution of consequences emerges. Since the Chernobyl accident there has been more interest in the use of numerical models as tools to assist in real‐time in emergency procedures if and when a nuclear accident occurs. However, the use of models in a real situation is distrusted by many people, who feel that the only way to assess an emergency situation is by making radiological measurements. This paper addresses uncertainties involved in modelling and argues that a combination of both approaches should be employed, using numerical modelling as an aid in intelligent interpretation of measurements, and suggesting priorities for international exchange of radiological dat

ISSN:0277-6693    

DOI:10.1002/for.3980100106

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe potential influence of increasing levels of atmospheric carbon dioxide (CO2) on water resources includes changes in evapotranspiration that result from control of stomatal resistance by CO2and changes in precipitation and temperature caused by ‘greenhouse’ warming. In this study we investigate the potential effects of CO2change on the hydrological response of a forested catchment in Shenandoah National Park, Virginia. Steady temporal trends are superimposed on stochastically derived time series of precipitation and temperature. These input data, which account for the natural variability of the system and the hypothetical effects of climate change, are then used to drive TOPMODEL, a variable‐source‐area hydrological model. A variety of climate‐change scenarios is simulated and temporal trends in annual average flow, peak flow, and basin yield are detected using Kendall's tau statistic. The direction and magnitude of the runoff trends are dependent on the relative magnitudes of the induced trends in precipitation, temperature, and stomatal resistance. Stochastic variability in temperature and precipitation obscure the runoff trends even when real trends in precipitation, temperature, and stomatal resistance are si

ISSN:0277-6693    

DOI:10.1002/for.3980100107

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractComplex models are often used to make predictions of environmental effects over a broad range of temporal and spatial scales. The data necessary to adequately estimate the parameters of these complex models are often not available. Monte Carlo filtering, the process of rejecting sets of mode! simulations that fail to meet prespecified criteria of model performance, is a useful procedure for objectively establishing parameter values and improving confidence in model predictions. This paper uses a foodweb model to examine the relationship between model sensitivities and Monte Carlo filtering. Results show that Monte Carlo filtering with a behavior definition that is closely related to the sensitivity structure of the model will produce substantial reductions in model forecasting uncertainty.

ISSN:0277-6693    

DOI:10.1002/for.3980100108

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractMost models of environmental systems can be expected to suffer, to a varying extent, from a lack of identifiability. Overparameterization seems both intrinsic and an intractable problem. As a result, interpretation of past observed behaviour through a model is ambiguous, and this will have obvious implications for any predictions of future behaviour. There has been much study of this issue of uncertainty in environmental modelling, yet very limited investigation of its consequences in the use of larger‐scale models. The paper examines some of these consequences for a model of the carbon and phosphorus cycles in Lake Ontario having 24 state variables and thirteen parameters. Filtering theory is used to provide both the conceptual framework for the analysis and a specific, recursive algorithm for the propagation of a variance‐covariance matrix of state prediction errors. Special attention is given to examining the ambiguities that may arise in the making of predictions, and the possibility of generating contradictory statements about future behaviour is introduced. It is found that with this relatively large model the propagation of prediction error variances is insensitive to the degree of correlation among the parameter‐estimation errors and to changes of the nominal estimated values of small subsets of param

ISSN:0277-6693    

DOI:10.1002/for.3980100109

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe issue of whether models developed for current conditions can yield correct predictions when used under changed control, as is often the case in environmental management, is discussed. Two models of different complexity are compared on the basis of performance criteria, but it appears that good performance at the calibration stage does not guarantee correctly predicted behavior. A requirement for the detection of such a failure of the model is that the prediction uncertainty range is known. Two techniques to calculate uncertainty propagation are presented and compared: a stochastic first‐order error propagation based on the extended Kalman filter (EKF), and a newly developed and robust Monte Carlo set‐membership procedure (MCSM). The procedures are applied to a case study of water quality, generating a projective forecast of the algal dynamics in a lake (Lake Veluwe) in response to management actions that forcethesystem into a different mode of behavior. It is found that the forecast from the more complex model falls within the prediction uncertainty range, but its informative value is low due to large uncertainty bounds. As a substitute for time‐consuming revisions of the model, educated speculation about parameter shifts is offered as an alternative approach to account for expected but unmodelled changes in the s

ISSN:0277-6693    

DOI:10.1002/for.3980100110

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractA storm surge barrier was constructed in 1987 in the Oosterschelde estuary in the south‐western delta of Holland to provide protection from flooding, while largely maintaining the tidal characteristics of the estuary. Despite efforts to minimize the hydraulic changes resulting from the barrage, it was expected that exchange with the North Sea, suspended sediment concentration and nutrient loads would decrease considerably. A model of the nutrients, algae and bottom organisms (mainly cockles and mussels) was developed to predict possible changes in the availability of food for these organisms. Although the model is based on standard constructs of ecology and hydraulics, many of its parameters are known with but low accuracy, being expressed as a range of possible values only. Running the model with all possible values of the parameters gives rise to a fairly wide range of model output responses. The calibration procedure used herein does not seek a single optimal value for the parameters but a decrease in the parameter range and thus a reduction in model prediction uncertainty. The field data available for calibration of the model are weighted according to their relationship with the model's objective, i.e. to predict food availability for shellfish. Despite the considerable physical changes resulting from the barrier food availability for shellfish is predicted to remain largely unchanged, due to the compensating effects of several other accompanying changes. There appears to be room for the extension of mussel culture, but at an increased risk of adverse conditions arisin

ISSN:0277-6693    

DOI:10.1002/for.3980100111

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY