WorkBlock 4 - Protocol for Multimodel Extremes Analyses: 2009_V2

Protocol 2009_V2 aims at a Multimodel Analysis of Hydrological Extremes as simulated by large-scale models. The analyses of extremes will only be done for the situation without major human impacts (e.g. dams, irrigation).

Content

• Spatial resolution and landmask
• Model period
• Atmospheric forcings
• Elevation, land use/cover, soil information
• Routing network
• Human impacts
• Data format
• Requested variables
• File naming convention
• Data submission

Spatial resolution and land mask
The spatial resolution, the grid cell midpoints and the standardized land mask for this model intercomparison are identical to WaterMIP (WaterMIP Spatial resolution and land mask).

Model period
In this first phase (i.e. second half of 20th Century, current climate), the modelling period should be 1958-2001 (WATCH Forcing Data available). The reporting period is 1963 – 2001, which should be preceded by 5 years (1958-1962) of spin-up.

Atmospheric forcings
The forcing data can be found on the Watch ftp site (folder WorkBlock1 - WATCH Forcing Data, see README file for information). The main variables are in 6-hourly or 3-hourly time steps, and at daily time step. NB: For rainf and snowf use the GPCC versions! This is identical to WaterMIP, except for the length of the period (WaterMIP Atmospheric forcings).

Elevation, land use/cover, soil information
For instructions on evaluation, land use/cover and soil information, see WaterMIP (WaterMIP Elevation, land use/cover, soil information).

Routing network
Use the same routing network as for WaterMIP. The same applies to the treatment of large lakes and associated cells (i.e. only transportation). (WaterMIP Routing network).

Human impacts
Hydrological extremes will only be compared for the situation without human influence.

Data format and data convention, file array structure and variable naming convention
See the link "Data Format" under Global Modeling for general information. Some additional information specific to WB4 Extremes can be found in paragraph "File naming convention and array structure" below.

Requested variables: WB4 Multimodel Extremes Analyses 2009_V1
All the requested output variables (Table 1) should be submitted as fields (gridded values) of daily values (44 years of 365 ¹) daily values, in total 16060 values for each grid cell and output variable) for land points and ocean points. Similar to WaterMIP, this should be submitted for land points and ocean point from -56 to 84 degrees latitude, and from -180 to 180 degrees longitude, i.e. 280 rows and 720 cols, or 201600 grid cells totally. Ocean points should be included because it makes visualizing the netCDF files easier. Like for WaterMIP, the variable names and units are to follow the ALMA protocol (http://www.lmd.jussieu.fr/~polcher/ALMA).

Table 1: Requested model output variables (see also menu "Data format" and http://www.lmd.jussieu.fr/~polcher/ALMA)

¹⁾ If your model subdivides Qsb (subsurface runoff, slow drainage component of runoff response, which includes gravity drainage and lateral base-flow) into a slow and a quick subsurface component, then we also would like to receive Qsb_slow: slow subsurface runoff (we will compute Qsb_quick = Qsb – Qb_slow). Please note that Qsb_quick is subsurface flow and not surface runoff (Qs)!. The variable names Qsb_slow and Qsb_quick are not included in the ALMA conventions.

File naming convention and array structure
One file should include only one variable when submitting the data. One file should include the time series of daily values for only one variable and for one year when submitting the data. For the period 1958-2001 and 10 variables this means 44*10 = 440 files.

Similar to WaterMIP, use only lowercase letters in the file names, since some netCDF viewers only accept lowercase letters in their filenames. The submitted time series of daily data for a particular year yyyy should use the following file naming convention, where variablename refers to the variable names used in the ALMA convention:

modelname_wfdnat_variablename_daily_yyyy.nc, e.g. gwava_wfdnat_evap_daily_1987.nc. Include only one year of data in one file.

Similar to WaterMIP, data are to be submitted for the area -56 to 84 degrees latitude, and from -180 to 180 degrees longitude, i.e. 280 rows and 720 cols, or 201600 grid cells totally. Write the outputs row-wise starting at -55.75 and -179.75, and ending at 83.75 and 179.75.

Naming convention in netCDF:

• x-dimension name: lon
• x-dimension units: degrees_east
• y-dimension name: lat
• y-dimension units: degrees_north
• t-dimension name: time
• t-dimension units: days, i.e. numbered from 1 to 365 for the daily fields (0 to 364 is also acceptable). Months should refer to calendar months, and not year/12 which is sometimes used.
• missing_value: 1.e+20f

Use the same naming of variables, similar to WaterMIP. For example:

• Long field name: Total evapotranspiration (Use the ALMA variable description)
• Short field name: Evap (Use the ALMA variable names, also for the state files!)
• Field units: kg/m²s (Use the ALMA variable units)

The size of one output file including one variable at monthly time steps for a 15 year period is about 138 MB (netcdf format, uncompressed). Zip-compressed the file size is less than 10 percent of the uncompressed file size. The size of one output file including one variable at daily time steps for a 1 year period is over 250 MB uncompressed.

Data submission
The estimated file size is 50-80 MB (netcdf, zipped). Total estimated storage for one model is about 4 GB. Similar to WaterMIP, the files are to be submitted in compressed formats. Please use the Linux/UNIX compress or gzip (GNU zip) to compress the output files. For those using Windows, WinZip is also acceptable.

Please note, the files should NOT be submitted to ftp.wur.nl! Information where to store will follow soon.

HvL/17 July2009

¹) Some models have 366 days in leap years.