Lesson 7 - Exploring gridded and NWM configurations

Overview

In this lesson we compare the differences between a gridded channel routing simulation and a cutout from the National Water Model (NWM) which uses a different channel routing method and has some differences in model physics and parameters.

Creating the simulation directory and running a baseline WRF-Hydro simulation

Below are the commands from lesson 2 to create the simulation direcory and run a WRF-Hydro simulation. This simulation will be run exactly as was done in Lesson 2 and will serve as our baseline simulation. We will modify run-time options in subsequent simulations in the lesson and compare the outputs.

Note that we are skipping the compile step here, and using the binary from lesson 2.

National Water Model configuration (NWM)

In this section we will discuss the differences between the National Water Model (NWM) configuration and the baseline Gridded configuration. Afterwards, we will run a NWM simulation and visualize some of the differences.

Create a NWM simulation directory

Compare the contents of the NWM simulation directory to the Gridded simulation directory

In this section we will compare the files in the NWM simulation directory to those in the Gridded simulation directory.

View the contents of the NWM simulation directory

View the contents of the Gridded simulation directory

Here we can see that at the top level the directories contents look the same. However, there are differences in the DOMAIN and RESTART directories.

View the contents of the NWM/DOMAIN directory

View the contents of the Gridded/DOMAIN directory

Explore the differences

Note the file differences in the NWM directory compared to the Gridded directory. Below is a table of these files and descriptions.

Filename Description Source Required
GWBASINS.nc 2D file defining the locations of groundwater basins pre-processing Required for gridded when the baseflow bucket model is turned on and user defined mapping is off
Route_Link.nc Channel reach parameters (contains ComID,gage ID & channel params) pre-processing Required if reach based routing is used (including user defined mapping)
nudgingParams.nc Parameters used for data assimilation streamflow nudging user defined No, and not available for gridded
spatialweights.nc Spatial weight file used to map fluxes to catchment objects distributed with NWM domain files When using user defined mapping

NOTE: We can ignore the Gridded/lake_shapes directory, it simply contains geospatial data used for creating the domain

Explore the namelist differences between the NWM and Gridded configurations

In this section we will explore the namelists differences between the NWM and Gridded configurations

View the difference between NWM namelist.hrldas and Gridded namelist.hrldas

View the difference between NWM hydro.namelist and Gridded hydro.namelist

Run the default Gridded and NWM simulations

In this section we will run default simulations for the NWM and Gridded configurations using our prepared simulation directories.

Step 1: Run the NWM simulation

Step 2: Run the gridded simulation

View the hydrographs

Load the xarray python package

Load the CHANOBS streamflow datasets

We are going to use the CHANOBS files because it will limit the number of grid cells to only those which we have specified have a gage.

Plot the hydrographs

Summary

The gridded default simulation more closely resembles the observations for the Irene event in the upstream catchment than the NWM default simulation. The differences are wrapped up in several aspects:

  1. The geogrids for NWM and geogrid are different, resulting in differences in some default geogrid parameters
  2. Fundamental differences in channel physics
  3. NWM undergoes a mapping process to transfer fluxes between the grids to the vector network (the spatial weights), whereas the gridded configuration has a 1:1 mapping.

If time permits...

View the CHANNELGRID variable from each Fulldom_hires.nc file for the NWM and Gridded domains using xarray.

Note the differences and be ready to discuss.

Congratulations!

This concludes lesson 7, our last hands on experiment.

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