Incorporating uncertainty into climate variability
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The Source Stochastic Analysis tool contains a model for the generation of daily rainfall data for multiple sites using the transition probability matrix (with Boughton’s correction). Stochastic climate data can be used as inputs into hydrological and ecological models to quantify uncertainty in environmental systems associated with climate variability. Additional stochastic data generation models will be added to the Stochastic Analysis tool in the future. For a detailed description of the multi-site, daily rainfall generation model refer to the Scientific Reference Guide.
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The Stochastic Analysis tool will automatically load the rainfall data that is being used by the scenario, and then stochastically generate rainfall replicates for each sub-catchment.
Figure 1. Configuration, Stochastic
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Analysis
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The Stochastic Analysis tool may take some time to complete, depending on the number of sub-catchments, replicates, number of recorded variables and type of rainfall data used in the scenario. Generally, the more complex the model or scenario, the longer the stochastic generation of rainfall data will be.
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Once the Stochastic Analysis tool has finished, the modelled flow and constituent parameters appear in the Recording Manager and can be viewed by selecting the parameter of interest in the right-hand column of the Recording Manager. The new Results Manager, which is the default viewer for single analysis, does not currently support stochastic analysis outputs.
However, the individual time series produced during a Stochastic Analysis run can be streamed direct to disk while the model is running. Before initiating the model run, go to Edit>>Scenario Options>>Simulation Results and tick on the option to Export Results After Run (Figure 2). This will stream a .res.csv file to the chosen folder on the hard drive, which can then be opened in Excel or viewed in any text editor. Be aware that the Stochastic Analysis tool can potentially generate very large amounts of data and so this may be a very large file.
Figure 2. Stream outputs to disk
Viewing and assessing statistical results
A list of all available statistics is displayed in the top, middle window under Statistics. To view a particular statistic, select it under Statistics to view the data as a box and whisker plot, which shows the spread of data. Figure 2 3 shows the monthly mean plot for one of the nodes in the model.
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23. Box plot of mean monthly flow replicates
Figure 3 shows how a box and whisker plot represents the distribution of data.
Figure 3. Box and whisker plot
A new screen appears with the stochastically generated flow and constituents replicates and statistical outputs (Figure 45).
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5. Stochastically generated flow replicates
Limitations and cautionary notes
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