Tutorial: Uncertainty in time series data

The Multi-sim tutorial is designed to address uncertainty in time series data, be they environmental forcing functions, fishing effort, biomass series or other, see the EwE User Guide guidelines for Multi-sim.. Use the Anchovy Bay true.ewemdb database (download). Open the database, and go to Ecosim > Tools > Multi-sim. The EwE Multi-sim can read in time series files with varying forcing functions. You can get the format for the CSV file to use if you click Example on the Multi-sim interface. For your own use, use that file derived from your own model. Here, we will instead download a zipped file that holds a folder with 20 CSV files. Each of these 20 have a time series of environmental productivity that is derived as auto-correlated values based on the original true time series values.

Download the zipped multisim csv.folder, unzip and place it somewhere (where you can find it again).

Figure 1. Top part of one of the Anchovy Bay time series files used for the Multi-sim analysis in this tutorial.

Each CSV file looks like this, only difference is that the values in the Fitting column varies between files, but any of the time series in file can be varied, if so desired.

Now check that the Fitting time series is applied to primary production. Go Ecosim > Input > Forcing function > Apply forcing (producer) and check that F2 is applied to primary producers (or apply it, if it is not).

Here’s a sample showing how the “Fitting” time series look for four of the CSV files,

Figure 2. Four series of auto-correlated time series for environmental productivity. The original time series is indicated in red on each plot.

On the Multi-sim interface, Input > Source folder, select Choose, and browse to find the folder with the CSV files that you just downloaded. Select the 20 CSV files, by clicking All in the right column.

On Output, select where you want Multi-sim to write output. Select which indicators you want to get output of, e.g., Biomass. Next click Run. Multi-sim will now run Ecosim 20 times, each time with a different time series for the environmental forcing function read in. If saving biomass as in this example, it will make a folder for each of the 20 runs, and save two files in each, biomass_annual.csv and biomass_monthly.csv. This structure lends itself easily for analysis in R.

Compare the time series in some of the output files, play!

There’s a log file saved that shows what Multi-sim has done, in Figure 3 is an example.

Figure 3. Log-file from Anchovy Bay Multi-sim run