The mesoscale Hydrological Model
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Data Preparation for mHM

Getting Started

To run mHM the user requires a number of datasets. The follwing subsection gives a short overview and references to freely available datasets.

Meteorological variables

Meteorological data is usually available from the weather services of the countries of modelling interest. Freely available alternatives are the EOBS (http://www.ecad.eu/download/ensembles/download.php) and the WATCH datasets (http://www.eu-watch.org/gfx_content/documents/README-WFDEI.pdf).

You may have difficulties finding measurement data for Potential Evapotranspiration (PET). One possible solution, would be to calculate PET from the much easier available variables mean, maximum and minimum air temperature, using the Hargreaves-Samani method.

The two meteorological variables which are needed:

Name Unit Temporal resolution
Precipitation \(\mathrm{mm}\) hourly to daily
Average air temperature \(^\circ \mathrm{C}\) hourly to daily

Dependent of the specification for the potential evapotranspiration (processCase(5)) additional meteorological variables may be need:

  • processCase(5) = 0 - PET is read from input.
  • processCase(5) = 1 - Hargreaves-Samani equation
  • processCase(5) = 2 - Priestley-Taylor equation
  • processCase(5) = 3 - Penam-Monteith equation
Name Unit Temporal resolution
0 - Potential evapotranspiration \(\mathrm{mm}\) hourly to daily
1 - Minimum air temperature \(^\circ \mathrm{C}\) daily
1 - Maximum air temperature \(^\circ \mathrm{C}\) daily
2 - Net radiation \( W\;m^{-2} \) daily
3 - Net radiation \( W\;m^{-2} \) daily
3 - Absolut vapur pressure of air \( Pa \) daily
3 - Windspeed \( m\;s^{-1} \) daily

Morphological variables

In addition to the Digital Elevation Models (DEM) usually provided by federal authorities, a number of free alternatives exists. SRTM data is available from 60° South to 60° North in a 3" (~ 90 m) resolution (http://srtm.csi.cgiar.org/), the ASTER-GDEM covers the entire globe with a resolution of 1" (http://gdem.ersdac.jspacesystems.or.jp/). Hydrographically corrected SRTM data and a number of derived products in different resolutions are available from the HydroSHEDS project (http://hydrosheds.cr.usgs.gov/index.php).

Soil and hydrogeological data is usually provided by the geological surveys. On the soil side the Harmonized World Soil Database would be a free alternative (http://webarchive.iiasa.ac.at/Research/LUC/External-World-soil-database/HTML/).

Name Unit Temporal resolution
Digital elevation model \(\mathrm{m}\) -
Soil maps with textural properties
(% sand and clay contents, bulk density per horizon,
and root depth zone)
- -
Geological maps with aquifer properties
(specific yield, permeability, aquifer thickness)
- -
Streamflow location \((\mathrm{m}, \mathrm{m})\) (lat,lon) -

Land Cover

Free land cover data is available from different sources. The Corine programm provides land cover scenes for Europe with resolutions of 100m and 250m (http://www.eea.europa.eu/publications/COR0-landcover), the Global Land Cover Map 2000 a dateset covers the entire world in a resolution of 1km.

Name Unit Temporal resolution
Land cover scenes - monthly to annual
Leaf area index - weekly to monthly

Gauging Station Information

Streamflow measurments should also be available from federal authorities. In addition, the Global Runoff Data Center provides timeseries of varying length for several thousand gauging stations all over the world (http://www.bafg.de/GRDC)

Name Unit Temporal resolution
Streamflow measurements \(\mathrm{m}^3 \mathrm{s}^{-1}\) hourly to daily

Optional Data

Name Unit Temporal resolution
Snow cover - daily to weekly
Land surface temperature \(\mathrm{K}\) daily to weekly
Groundwater station location \((\mathrm{m}, \mathrm{m})\) (lat,lon) -
Groundwater head measurements \(\mathrm{m}\) weekly to monthly
Eddy covariance station location \((\mathrm{m}, \mathrm{m})\) (lat,lon) -
Eddy covariance measurements \(\mathrm{m}\) hourly

Preparation of the Forcings

Forcing data should be available from federal databases like DWD for Germany. Be sure to bring data in the netcdf format, like


These files can be edited with the CDO module package in order to select or change data. Please read the according CDO and NCKS reference sheets for details and make sure to load the CDO modules before starting.

Extract Data to the Size of a Catchment

Let FULLMAP.nc be the the forcing data of a region much greater than your catchment. Let X1, X2, Y1, Y2 be the coordinates (lon and lat) of a rectangular overlapping the catchment. The forcing data MAP.nc for your catchment can be extracted by the CDO command:

cdo sellonlatbox,X1,X2,Y1,Y2 FULLMAP.nc MAP.nc

Optionally, certain pixels can be extracted, too:

ncks -d x,1,1 -d y,2,2 MAP.nc PIXEL.nc

Extact Data to the Time Period of Interest

Let MAP.nc be the forcing data including your period of interest. Let DATE1 and DATE2 be the starting and ending dates of your period, respectively. Their date format is YYYY-MM-DD. The data PERIOD.nc can be extracted by the CDO command:

cdo seldate,DATE1,DATE2 MAP.nc PERIOD.nc

Please note that a reference date according to DATE1 should be provided in PERIOD.nc:

cdo setreftime,DATE1,00:00:00,days PERIOD.nc FINAL.nc

Data Types

Any data provided for mHM should be of the data type DOUBLE. You should convert all data related to a variable VAR (e.g. tavg) with the following CDO command:

cdo -b F64 selname,VAR FINAL.nc FINAL64.nc

The only exception here is the time, its data type has to be INTEGER. This can be changed with NCAP2:

ncap2 -s 'time=int(time)' STILLNOTFINAL.nc FINAL.nc

Variable Names

In mHM the variable names of the forcing are hard-coded. They need to be

  • "tavg" for average temperature
  • "pre" for precipitation
  • "pet" for evapotranspiration

For example, you can change the variable name TEMPERATURE in your NETCDF file with the following CDO command:


The Header File

Every meteorological data file should come with an additional file "header.txt" in the same directory. In the following example, we has only one pixel of data (ncols=nrows=1) and a cell size of 4km. The easting and northing coordinates of the lower left cornaer should be similar to the morphological data of your catchment.

ncols 1
nrows 1
xllcorner 639357.3
yllcorner 5723706.2
cellsize 4000
NODATA_value -9999

NODATA values

In order to be consistent in your data, you should specify the same NODATA value everywhere. For example, specify "-9999" in your header file as NODATA value. Usually, this should be changed also in NC files by the ncatted command. The following example overwrites or adds (o) the NODATA attribute "_FillValue" with value "-9999" of type double (d) to the variable "pre":

ncatted -O -a _FillValue,pre,o,d,-9999. INOUT.nc

Preparation of the LatLon Grid

As input mHM additionally needs a latlon.nc file specifying the geographical location of every grid cell in WGS84 coordinates. This file has to be adjusted for every resolution of the level-1 hydrological simulations.

For creating a latlon file mHM comes with the python script create_latlon.py, which can be found in pre-proc/. Detailed information for the usage of this python script can be found in the online help by typing:

python [MHM_DIRECTORY]/pre-proc/create_latlon.py -h

create_latlon.py needs several specifications via command line switches. First, the coordinate system of the morphological and meteorological data have to be specified according to www.spatialreference.org by using the switch: -c. Second, you need to specify three header files containing the corresponding information for the different spatail resolutions connected to mHM. The three resolutions are the resoltution of 1) the morphological input (switch: -f), 2) the hydrological simulation (switch: -g), and 3) the routing (switch: -e).

These header files can be produced by adopting the header file of the meteorological data Therefore, copy one of these files that you generated for meteo data (see Preparation of the Forcings):

cp [INPUT_DIRECTOY]/input/meteo/pre/header.txt [INPUT_DIRECTORY]/input/latlon/

Edit the new file header.txt such that cellsize equals your hydrologic resolution. You have to adapt ncols and nrows to that resolution such that it covers the whole region. For example, reducing the cell size from 2000 to 100, the number of columns and rows should be increased by a factor of 20.

Third, you need to set the path and filename for the resulting output file by using the switch -o.

An example for creating a lat-lon-file looks like

python [MHM_DIRECTORY]/pre-proc/create_latlon.py -c epsg:31463 -f header_100m.txt -g header_1000m.txt -e header_2000m.txt -o ../latlon/latlon.nc

Keep in mind that you need one latlon file for each hydrologic resolution in mHM. Since the filename latlon.nc is hard-coded in mHM, we recommend to create different directories for each resolution you need, containing the related header and latlon file.

Preparation of the Morphological Data

MHM needs several morphological input datasets. All these have to be provided as raster maps in the ArcGis ascii-format, which stores the above header and the actual data as plain text. Some of the raster files need to be complemented by look-up tables providing additional information. The tables and their structure are described in more detail in subsection Table Data. Take care of the follwing limitations to mHM input data during data processing:

  • All gridded input, i.e. your morphological and your meteorological data, needs to cover the same spatial domain. That means, that the values xllcorner, yllcorner, xllcorner+ncols*cellsize and yllcorner+nrows*cellsize have to be identical for all files!
  • MHM allows you to provide your meteorological forcing in a different horizontal resolution than the morphological data. The larger cellsize however needs to be a multiple of the smaller.

The required datasets and their corresponding filenames:

Description Raster file name Table file name
Sink filled Digital Elevevation Model (DEM) dem.asc -
Slope map slope.asc -
Aspect Map aspect.asc -
Flow Direction map fdir.asc -
Flow Accumulation map facc.asc -
Gauge(s) position map idgauges.asc [gauge-id].txt
Soil map soil_class.asc soil_classdefinition.txt
Hydrogeological map geology_class.asc geology_classdefinition.txt
Leaf Area Index (LAI) map LAI_class.asc LAI_classdefinition.txt
Land use map your choice -

A possible GIS workflow

In the following paragraphs a possible GIS workflow is outlined using the software ArcMAP 10 with the Spatial Analyst Extension and optionally the Arc Hydro Tools (http://downloads.esri.com/blogs/hydro/AH2/ArcHydroTools_2_0.zip)

General considerations

  • As the spatial discretizations (i.e. resolutions, origin) of your datasets will most likely differ, it is recommended to set the following envirnmental settings on every processing step outlined in the following paragraphs.
    Button 'Environments...' in all Toolbox windows
    Point to the largest of your input data grids in 'Extent' and 'Snap Raster', which is usually the dataset with the coarsest horizontal resolution. In the likely case, that this is your meteorological input, create a grid from any of your netcdf-files first.
    System Toolboxes -> Multidimension Tools -> Make NetCDF Raster Layer
    Save the output grid (right click the raster in the 'Table of Contents' -> 'Data' -> 'Export Data...').
  • If the map projections of your datasets differ, a harmonization of these becomes necessary. Repeat the depicted step to convert all your input files. Which projection to choose is highly dependent on your simulation domain and size. For the current model version an equal-area projection is strongly recommended.
    System Toolboxes -> Data Management Tools -> Projections and Transformations -> Raster -> Project Raster
  • If your input datasets are not already in the desired level-0 resolution, resample the DEM, the hydrogeological, LAI, soil and land use maps. Choosing an appropiate resolution depends on data quality and needed level of simulation detail, but keep in mind that:
  1. Your different input resolution levels must be multiples of each other. E.g. you should choose a level-0 resolution of 100m (instead of 90m in case you are using SRTM data) if your meteorological input resolution is 4km.
  2. Model runtime directly depends on the number of grid cells.
System Toolboxes -> Data Management Tools -> Raster -> Raster Processing -> Resample

  • It is important that all your morphological input files exactly cover the same spatial domain. That also means that if a cell contains valid data in any one of the datasets, the very same cell must also be definied in all the others. One possibility to solve this typical problem would be to set such 'doubtful' cells to the corresponding NODATA_value. Therefore create a mask as depicted below, which only contains cells, that are defined everywhere.
    System Toolboxes -> Spatial Analyst Tools -> Map Algebra -> Raster Calculator
  • Mask all the mentioned datasets with the output of the 'Raster Calculator' follwing the procedure described in Mask the datasets of this tutorial. In case the described processing step is necessary, accomplish it before you reach subsection Flow direction and flow accumulation ! Masking these maps would most likely disturb the hydrological properties of your catchment data and result in unexpected model behaviour.

Slope map

System Toolboxes -> Spatial Analyst Tools -> Surface -> Slope

Aspect map

System Toolboxes -> Spatial Analyst Tools -> Surface -> Aspect

Fill DEM sinks

System Toolboxes -> Spatial Analyst Tools -> Hydrology -> Fill

Flow direction and flow accumulation

Depending on quality and resolution of the DEM map, these steps can be done with the respective tools from the Spatial Anaylst Extension or by using the Arc Hydro Tools.

Spatial Analyst

If a high quality DEM, with a resolution fine enough to represent small scale river morphology is available, you may calculate flow direction and flow accumulation directly.

  • Flow Directon
    System Toolboxes -> Spatial Analyst Tools -> Hydrology -> Flow Direction
  • Flow Accumulation
    System Toolboxes -> Spatial Analyst Tools -> Hydrology -> Flow Accumulation

Arc Hydro Tools

Using the Arc Hydro Tools is recommended in case of doubtful DEM quality and/or coarse map resolutions.

  • In a first step the original DEM must be reconditioned, i.e. the given altitudes will be reassigned in dependence of a stream network. The latter must be given as a Line Shapefile. In case the necessary stream network file is not available, you can get one from the USGS HydroSHEDS download portal http://hydrosheds.cr.usgs.gov/dataavail.php.
    System Toolboxes -> Arc Hydro Tools -> Terrain Preprocessing -> DEM Reconditioning
  • Fill the sinks in the resulting reconditioned DEM
    System Toolboxes -> Arc Hydro Tools -> Terrain Preprocessing -> Fill Sinks
  • Calculate Flow Direction
    System Toolboxes -> Arc Hydro Tools -> Terrain Preprocessing -> Flow Direction
  • Create a Flow Accumulation map
    System Toolboxes -> Arc Hydro Tools -> Terrain Preprocessing -> Flow Accumulation

Gauges map

  • Assuming that you have the positions of your gauges in a table, which has at least the colums x, y, id (in any order and/or amongst other columns), you are able to to convert your data into a Point Shapefile. Choose the appropiate fields and do not forget to set the coordinate system information.
    Right click on the table in Arc Catalog - > Create Feature Class -> From XY Table
  • Check the positions of your gauges against the previously created Flow Accumulation map. If the points do not exactly match the stream-like features on the Flow Accumulation grid, edit the Shapefile (right click on the Point Feature in the Table of Contents -> Edit Features -> Start Editing) and move the gauges to do so. Changing the depiction of the Flow Accumulation map might facilitate this step (i.e. right click the Flow Accumulation map in the Table of Contents -> Properties -> Tab 'Symbology' -> Choose 'Stretched' in the 'Show' box on the left hand side and Type 'Standard Deviations' in the center box. It might also be necessary to invert the color ramp by (un-)checking the 'Invert' check box). Remember to stop the editing process and save your edits (Editor Toolbar -> Editor -> Stop Editing).
    Mismatching gauges (left) should be replaced (right)
  • Convert the resulting shapefile into an raster map with level-0 resolution.
    System Toolboxes -> Conversion Tools -> To Raster -> Point to Raster

Watershed delineation

  • Edit the (possibly corrected) gauges shapefile created during the last processing step again and remove all but the outlet gauge. If you need the unedited file, create a copy of the original Shapefile before editing it.
  • Delineate the basin
    System Toolboxes -> Spatial Analyst -> Hydrology -> Watershed

Mask the datasets

Mask all mHM input raster files with the created watershed mask

System Toolboxes -> Spatial Analysis Tools > Extraction > Extract by Mask

Write the ascii grids

Convert the processed and masked raster maps into ASCII files

System Toolboxes -> Conversion Tools -> From Raster -> Raster to ASCII

Land Cover Data

Unlike the other classified datasets (soils, hydrogeology, LAI), where as much information as available can be added, the land use data is restricted to three different classes, which are listed below:

Class Description
1 Forest
2 Impervious
3 Pervious

Table Data

As previously stated, the input datasets 'soil_class.asc', 'geology_class.asc', 'idgauges.asc' and 'LAI_class.asc' need to be complemented by look-up-tables. All these look-up tables specify the total number of classes/units to read in the very first line, following the keywords 'nSoil_Types', 'nGeo_Formations' and 'NoLAIclasses' respectively. The second line acts as a header describing the contents of the following data. In the subsection The soil look-up table The hydrogeolgy look-up table and The LAI look-up table screenshots of shorted, but sufficient table files are presented. All fields are further listed and described in the repective tables.

The soil look-up table

A possible 'soil_classdefinion.txt' file

Field Description
MU_GLOBAL Soil id as given in the corresponding 'soil_class.asc' map. All raster map ids must be given here
HORIZON Horizon number starting at the top of the soil column.
Your are free to provide any number of horizons for each soil individually
UD[mm] Upper depth of the horizon in millimeter.
Should be 0 for the first, and the lower depth of the superimposing horizon for all others
LD[mm] Lower depth of the horizon in millimeter
CLAY[%] Clay content in percent
SAND[%] Sand content in percent
BD[gcm-3] Mineral bulk density in grams per cubic centimeter

The hydrogeolgy look-up table

A possible 'geology_classdefinion.txt' file

Field Description
GeoParam(i) Parameter number of the formation, the link to 'mhm_parameter.nml'
ClassUnit Class id as present in the 'hydrogeology_class.asc' raster map
Karstic Presence of karstic formation (0: False, 1: True)
Description Text description of the unit

The LAI look-up table

A possible 'LAI_classdefinion.txt' file

Field Description
ID LAI class id as given in the file LAI_class.asc
LAND-USE Description of the LAI class
Jan. to Dec. Monthly LAI values

The gauge files

A possible gauge file

The structure of the gauge files is different from the look-up tables listed so far. The following table describes its content.

Line Description
1 Gives basic information about the gauging station (Station-Id:Station-Name/River-Name)
2 Specifies the nodata value
3 The number of measurements per day
4 The start date of the time series in the format given in parentheses
5 The end date of the time series in the format given in parentheses
6 to end The measurement data in cubic meter per second
preceded by the actual date in the same format as the dates of lines four and five

For every gauge id given in 'idgauges.asc' one gauge file has to be created as outlined above. The file name has to exactly reflect the gauge id and carry a '.txt' extension. The table data file for a gauge with an id of 0343 in 'idgauges.asc' should therfore be named '0343.txt'.

Post-GIS preparation

Make sure that all decimals are indicated with dots, not commas:

perl -i.bak -pe 's/\,/\./g' *.asc

Make sure that accuracy of your llcorners is reasonable. For example, the following code removes all but one digits after the dot:

perl -i.bak -pe 's/(^[xy].+)\.(\d)\d+/$1\.$2/g' *.asc

Make sure that your files cover the same spatial domain. In case your grid origins match, but you are missing rows and columns, the perl script pre-proc/enlargegrid.pl will pad your data at the top and the right end of the grid.

/basin/input/morph/$ ~/mhm/pre-proc/enlargegrid.pl aspect.pl
31 rows with 47 cols.
/basin/input/morph/$ ~/mhm/pre-proc/enlargegrid.pl 50 40
/basin/input/morph/$ ~/mhm/pre-proc/enlargegrid.pl aspect.pl
40 rows with 50 cols.
Python bindings of mHM.
Definition __init__.py:1

If your data differs more substantially the program 'mHM/pre-proc/resize_grid.py' will harmonize your grids.

python match_grids.py source_grid target_grid out_grid

The script takes three Input arguments:

  1. The source grid to be enlarged
  2. The target grid which could also be an header file as described in subsection The Header File
  3. An output file

The program will fail, if your target grid is smaller than the source grid or if the cellsizes of both grids are not divisable. If necessary the source grid will be shifted in order to make both origins match. This 'shift' is only accomplished by changing the values of the corner coordinates, no real interpolation will be done.