Ensemble Streamflow Prediction (ESP)

OMS provides an Ensemble Streamflow Prediction (ESP) simulation type. This is a modified version of the National Weather Service’s ESP procedure (Day, 1985). ESP uses historic or synthesized meteorological data as an analogue for the future. These time series are used as model input to simulate future conditions.

The typical application of ESP is to forecast streamflow. The initial hydrologic conditions of a watershed, for the start of a forecast period, are assumed to be those simulated by the model for that point in time. Typically, multiple hydrographs are simulated from this point in time forward, one for each year of available historic data. For each simulated hydrograph, the model is re-initialized using the watershed conditions at the starting point of the forecast period. The forecast period can vary from a few days to an entire year. A frequency analysis is then performed on the peaks and/or volumes of the simulated hydrograph traces to evaluate their probabilities of exceedance.

The ESP procedure uses historical meteorological data to represent future meteorological data. Alternative assumptions about future meteorological conditions can be made with the use of synthesized meteorological data. A few options are available in applying the frequency analysis. One option assumes that all years in the historic database have an equally likely probability of occurrence. This give equal weight to all years. Years associated with El Nino, La Nina, ENSO neutral, Pacific Decadal Oscillation (PDO) less than -0.5, PDO greater than 0.5, and PDO neutral have also been identified in the ESP procedure, and the years in these groups can be extracted separately for analysis. Alternative schemes for weighting user-defined periods, based on user assumptions or a priori information, are also being investigated.

Create an ESP Simulation

To create an ESP Simulation, select File | New File to open the New File wizard.

In the New File wizard, select Simulations and then select Ensemble Streamflow Prediction (ESP). Then click on Next and the New Ensemble Streamflow Prediction (ESP) window appears.

In the New Ensemble Streamflow Prediction (ESP) window, enter a name to replace the default File Name newESPScenario. Tne click on Finish. An ESP Simulation with the new name is now added to the Simulations folder of the OMS Project.

Run the ESP Simulation

TO run the ESP Simulation, open the Simulation directory and double click on the ESP Simulation name you have just created. This will open the Simulation window below. The name of the Simulation in this example is tetonDriggs_ESP.

The fields to be completed in this window are as follows:

Model File

The model to be used in this simulation. Drag and Drop a model file from your Project Models directory into this field.

Initialization Period

Provide a start and end time for ESP initialization. This is period over which the model will be run prior to the forecast period. It should be long enough to run the model through one or more wetting and drying cycles.

Forecasting Period

Provide the end date for your forecasting period. (Note: The start date for the forecasting period follows the end date of the initialization period.)

Historical Years

Provide the historical years to be used for forecasting traces.

Model parameter files

Provide all the parameter files for the model. One of those files must have the ESP property set and content as described in the next section.

Note: if there is invalid input for any of the ESP parameter, the number of years/days will appear in read. You can still save invalid setting, however you cannot execute.

Attribute Management for ESP

An ESP simulation requires an additional parameter info that describes the model attributes which should be managed in ESP.

A ESP specific property set needs to be defined in one of the existing simulation CSP files, or in a separate CSP file. All attribute names and the model name that are relevant for ESP are listed.

In the example above the parameter file tetonDriggs_esp.csp contains the following settings:

@Properties, ESP
 created at, "Thu Apr 17 09:44:49 MDT 2008"
 created by, olafdavid

# managed attributes by ESP
# name of the attribute that manages the start time. 
@Property, attrStartTime,  "startTime"

# name of the attribute that manages the end time. 
@Property, attrStopTime,   "stopTime"

# name of the attribute that manages the input file
@Property, attrInputFile,  "inputFile"

# name of the attribute that manages the output file. 
@Property, attrOutputFile, "outFile"

# name of the scope that defines the attributes above. 
@Property, attrScope, "prms_xyz"

ESP Execution

Executing an ESP Simulation can be accomplished by selecting the Run | Run File pull down menu as shown below.

The Simulation can also be run by selecting the Run toolbar. When using the tool bar, the ESP Simulation tab or the ESP file node must be focused to enable execution.

Note that the output of an ESP run might look intermingled. All separate ESP trace runs are executed in parallel and output will be printed as it happens in each model run. Avoiding console output in a model that runs in ESP is good practice.

ESP Analysis