Simple software processes and tests improve the reliability and usefulness of a model.

Models are abstractions of reality that have predetermined limits (often not consciously thought through) on what problem domains the models can be used to explore. These limits are determined by the range of observed data used to construct and validate the model. However, it is important to remember that operating the model beyond these limits, one of the reasons for building the model in the first place, potentially brings unwanted behaviour and thus reduces the usefulness of the model. Our experience with the Agricultural Production Systems Simulator (APSIM), a farming systems model, has led us to adapt techniques from the disciplines of modelling and software development to create a model development process. This process is simple, easy to follow, and brings a much higher level of stability to the development effort, which then delivers a much more useful model. A major part of the process relies on having a range of detailed model tests (unit, simulation, sensibility, validation) that exercise a model at various levels (sub-model, model and simulation). To underline the usefulness of testing, we examine several case studies where simulated output can be compared with simple relationships. For example, output is compared with crop water use efficiency relationships gleaned from the literature to check that the model reproduces the expected function. Similarly, another case study attempts to reproduce generalised hydrological relationships found in the literature. This paper then describes a simple model development process (using version control, automated testing and differencing tools), that will enhance the reliability and usefulness of a model

The value of skill in seasonal climate forecasting to wheat crop management in a region with high climatic variability

In Australia, and particularly in the northern part of the grain belt, wheat is grown in an extremely variable climate. The wheat crop manager in this region is faced with complex decisions on choice of planting time, varietal development pattern, and fertiliser strategy. A skilful seasonal forecast would provide an opportunity for the manager to tailor crop management decisions more appropriately to the season. Recent developments in climate research have led to the development of a number of seasonal climate forecasting systems. The objectives of this study were to determine the value of the capability in seasonal forecasting to wheat crop management, to compare the value of the existing forecast methodologies, and to consider the potential value of improved forecast quality. We examined decisions on nitrogen (N) fertiliser and cultivar maturity using simulation analyses of specific production scenarios at a representative location (Goondiwindi) using long-term daily weather data (1894-1989). The average profit and risk of making a loss were calculated for the possible range of fixed (i.e. the same every year) and tactical (i.e. varying depending on seasonal forecast) strategies. Significant increase in profit (up to 20%) and/or reduction in risk (up to 35%) were associated with tactical adjustment of crop management of N fertiliser or cultivar maturity. The forecasting system giving greatest value was the Southern Oscillation Index (SOI) phase system of Stone and Auliciems (1992), which classifies seasons into 5 phases depending on the value and rate of change in the SOI. The significant skill in this system for forecasting both seasonal rainfall and frost timing generated the value found in tactical management of N fertiliser and cultivar maturity. Possible impediments to adoption of tactical management, associated with uncertainties in forecasting individual years, are discussed. The scope for improving forecast quality and the means to achieve it are considered by comparing the value of tactical management based on SOI phases with the outcome given perfect prior knowledge of the season. While the analyses presented considered only one decision at a time, used specific scenarios, and made a number of simplifying assumptions, they have demonstrated that the current skill in seasonal forecasting is sufficient to justify use in tactical management of crops. More comprehensive studies to examine sensitivities to location, antecedent conditions, and price structure, and to assumptions made in this analysis, are now warranted. We have examined decisions related only to management of wheat. It would be appropriate to pursue similar analyses in relation to management decisions for other crops, cropping sequences, and the whole farm enterprise mix

Simplifying environmental model reuse

The environmental modelling community has developed many models with varying levels of complexity and functionality. Many of these have overlapping problem domains, have very similar 'science' and yet are not compatible with each other. The modelling community recognises the benefits to model exchange and reuse, but often it is perceived to be easier to (re)create a new model than to take an existing one and adapt it to new needs. Many of these third party models have been incorporated into the Agricultural Production Systems Simulator (APSIM), a farming systems modelling framework. Some of the issues encountered during this process were system boundary issues (the functional boundary between models and sub-models), mixed programming languages, differences in data semantics, intellectual property and ownership. This paper looks at these difficulties and how they were overcome. It explores some software development techniques that facilitated the process and discusses some guidelines that can not only make this process simpler but also move models towards framework independence. Crown Copyright © 2008

Infusing the use of seasonal climate forecasting into crop management practice in North East Australia using discussion support software

Seasonal climate forecasting offers potential for improving management of crop production risks in the cropping systems of NE Australia. But how is this capability best connected to management practice? Over the past decade, we have pursued participative systems approaches involving simulation-aided discussion with advisers and decision-makers. This has led to the development of discussion support software as a key vehicle for facilitating infusion of forecasting capability into practice. In this paper, we set out the basis of our approach, its implementation and preliminary evaluation. We outline the development of the discussion support software Whopper Cropper, which was designed for, and in close consultation with, public and private advisers. Whopper Cropper consists of a database of simulation output and a graphical user interface to generate analyses of risks associated with crop management options. The charts produced provide conversation pieces for advisers to use with their farmer clients in relation to the significant decisions they face. An example application, detail of the software development process and an initial survey of user needs are presented. We suggest that discussion support software is about moving beyond traditional notions of supply-driven decision support systems. Discussion support software is largely demand-driven and can compliment participatory action research programs by providing cost-effective general delivery of simulation-aided discussions about relevant management actions. The critical role of farm management advisers and dialogue among key players is highlighted. We argue that the discussion support concept, as exemplified by the software tool Whopper Cropper and the group processes surrounding it, provides an effective means to infuse innovations, like seasonal climate forecasting, into farming practice

APSIM: A novel software system for model development, model testing and simulation in agricultural systems research

APSIM (Agricultural Production Systems Simulator) is a software system which allows (a) models of crop and pasture production, residue decomposition, soil water and nutrient flow, and erosion to be readily re-configured to simulate various production systems and (b) sail and crop management to be dynamically simulated using conditional rules. A key innovation is change from a core concept of a crop responding to resource supplies to that of a soil responding to weather, management and crops. While this achieves a sound logical structure for improved simulation of soil management and long-term change in the soil resource, it does so without loss of sensitivity in simulating crop yields. This concept is implemented using a program structure in which all modules (e.g. growth of specific craps, soil water, soil N, erosion) communicate with each other only by messages passed via a central 'engine'. Using a standard interface design, this design enables easy removal, replacement, or exchange of modules without disruption to the operation of the system. Simulation of crop sequences and multiple crops are achieved by managing connection of crop growth modules to the engine

Preliminary wind analysis regarding different speed ranges in the city of La Plata, Argentina

La Plata city (approximately 800 000 inhabitants) has intense traffic and industrial activity; nevertheless, the city has no governmental air monitoring network for air pollutants and winds have been scarcely studied. Wind observations provided here (covering 1998- 2007) belong to a weather station that was contrasted against the unique governmental site in the city area (the Airport). The present preliminary study analyses wind direction frequencies according to wind speeds and emphasizes wind patters within the first hour after calm occurrences. Results show that independently of the wind speed, wind direction frequency roses are in general similar to each other. Low wind speeds may occur most of the time (on average 58.2 %) and together with calm occurrences (on average 17.1% ) constitute an important factor for the accumulation of air pollutants. The proposed "outgoing of calm" wind direction frequency roses were found to be appropriate to gain knowledge in the structure of winds that transport pollutants towards exposed population after calm occurrences. Long term systematic meteorological fieldworks should be encouraged in the future so as to provide better tools for environmental modeling.A cidade de La Plata (aproximadamente 800.000 habitantes) tem tráfego e atividade industrial intensos. Contudo, não tem uma rede oficial de monitoramento para os contaminantes do ar e os ventos têm sido pouco estudados. As observações dos ventos aqui apresentadas (desde 1998 até 2007) correspondem a uma estação meteorológica que foi comparada com o único sitio oficial de registros de ventos na área urbana (o Aeroporto). O presente estudo preliminar analisa as frequências das direções do vento, segundo as suas velocidades, e coloca ênfase nos padrões de vento na primeira hora após as ocorrências calmarias. Os resultados mostram que as rosas de frequências de direções de ventos são em geral similares entre elas independentemente das velocidades. Velocidades baixas de ventos são factíveis de acontecer na maior parte do tempo (na média 58,2%), e, junto com as ocorrências de calmarias (na média 17,1%), constitui um fator importante para acumulação dos contaminantes. As rosas de frequência de direções de ventos propostas, nomeadas "saída de calmarias", resultaram ser apropriadas para o conhecimento da estrutura dos ventos que transportam os contaminantes acumulados em direção à população exposta, após períodos de calmaria. Na meteorologia deveriam se incentivados os trabalhos de campo sistemáticos, de longo prazo, de forma a prover melhores ferramentas para a modelagem de meio ambiente