In this file, the details of the dataset is explained.
The global ERA5 dataset is located under the following directory accessible from Compute Canada (CC) Graham Cluster:
/project/rpp-kshook/CompHydCore/climateForcingData/ERA5/ERA5_for_SUMMA/2_merged_data # rpp-kshook allocation
/project/rrg-mclark/data/meteorological-data/era5 # rrg-mclark allocationand the structure of the dataset hourly files is as following:
/project/rpp-kshook/CompHydCore/climateForcingData/ERA5/ERA5_for_SUMMA/2_merged_data
├── ERA5_merged_195001.nc
├── ERA5_merged_%y%m.nc
├── .
├── .
├── .
└── ERA5_merged_202012.ncThe coordinate variables of the ERA5 simulations are longitude and latitude representing the longitude and latitude points, respectively.
The time-stamps are included in the original files.
The NetCDF files of the dataset contain 7 variables needed to force hydrological models. You may see a list of variables by using the ncdump -h command on one of the files:
foo@bar:~$ module load cdo/2.0.4
foo@bar:~$ module load nco/5.0.6
foo@bar:~$ ncdump -h /project/rpp-kshook/CompHydCore/climateForcingData/ERA5/ERA5_for_SUMMA/2_merged_data/ERA5_merged_195001.ncThe spatial extent of the ERA5 is on latitutes from +90 to -90 and longitudes from -180 to 179.75. The resolution is 0.25 degrees.
The time-steps are hourly covering from January 1950 to December 2020.
In most hydrological modelling applications, usually 7 variables are needed detailed as following: 1) specific humidity, 2) surface pressure, 3) air temperature, 4) wind speed, 5) precipitation, 6) downward short wave radiation, and 7) downward long wave radiation. These variables are available through the current ERA5 dataset and their details are described in the table below:
| Variable Name | ERA5 Variable | Original Shortname | Parameter ID | Unit | IPCC abbreviation | Comments |
|---|---|---|---|---|---|---|
| surface pressure | airpres | sp | 134 | Pa | ps | |
| specific humidity @10m | spechum | q | 133 | kg/kg | huss | |
| air temperature@10m | airtemp | t | 130 | k | tas | |
| wind speed @10m | windspd | u,v | 131,132 | m/s | wspd | WIND=SQRT(u2+v2) |
| precipitation | pptrate | mtpr | 235055 | mm/hr | mean total precipitation rate | |
| short wave radiation | SWRadAtm | msdwswrf | 235035 | W m-2 | rsds | |
| long wave radiation | LWRadAtm | msdwlwrd | 235036 | W m-2 | rlds |
For a complete catalog of the dataset, see here.
The scripts to download the original ERA5 data are contained in the ERA5_downloads.zip file located in the current directory of the repository. The scripts are written by Quoqiang Tang and Wouter Knoben as part of the Community Workflows to Advance Reproducibility in Hydrological Modelling (CWARHM). "ERA5 data preparation includes interactions between an atmospheric model and a land surface model. ... [Original] ERA5 data is available at 137 different pressure levels (i.e. some height above the surface), as well as at the surface. The lowest atmospheric level is L137, at geopotential and geometric altitude 10m and data here relies only on the atmospheric model. Any variables at a height lower than L137 (i.e., at the surface) are the result of interpolation between atmospheric model and land model. We want to use only the outcomes from the ECMWF atmospheric model [...]. Therefore, we obtain (1) air temperature, (2) wind speed and (3) specific humidity at the lowest pressure level (L137), (4) Precipitation, (5) downward shortwave radiation, (6) downward longwave radiation and (7) air pressure are unaffected by the land model coupling and can be downloaded at the surface level. This is beneficial because surface-level downloads are substantially faster than pressure-level downloads. 1"