NetCDF Fill Value Type Mismatch in IO module

[hellkite500]

Expected Behavior

Program executes normally using netcdf fortran (4.5.2) and netcdf C (4.7.1)

Current Behavior

Using latest netcdf fortran (4.5.2) and netcdf C (4.7.1) the program crashes with the following error:
The job is stopped due to the fatal error. ERROR: Unable to place Fill value attribute into variable zwattablrt!

Possible Solution

Two possible solutions (will try to submit PR later) exist. One is to replace netcdf variable types
for definitions of compressed variables, i.e. replace nf90_int in lines like this with nf90_int64.

wrf_hydro_nwm_public/trunk/NDHMS/Routing/module_NWM_io.F

Line 835 in fb60447

iret = nf90_def_var(ftn,trim(fileMeta%varNames(iTmp)),nf90_int,dimId(1),varId)

There are at least 7 palces in module_NWM_io where this exists, may also be other places in the I/O code affected by netcdf_int types. I have tested this using the described netcdf libraries, and it works.

This may not work with netcdf fortran 4.4.4 (see issue linked below). If it doesn't then the fileMeta%fillComp variable should be a 4 byte instead of 8 byte int that it currently is. I think that netcdf fortran 4.4.4 is doing this conversion, but when full support for 64 bit ints was added, the behavior in the library changed and this became an explicit error.

Also, the nwmcheck function that reports the errors should report the netcdf error number and/or the string message from nf90_strerror which would give information like this: NetCDF: Not a valid data type or _FillValue type mismatch

Steps to Reproduce (for bugs)

1. Link against netcdf fortran 4.5.2 (I think anything over 4.4.4 will reproduce, but not confirmed)
2. Turn on i/o compression option in hydro.namelist
3. Run model

Your Environment

• Version of the code used: Discovered on the NWM 2.0 beta relase tag (6fe9fa3). Investigating code on master, issue is still present, but not explicitly verified.
• Operating System and version: Alpine 3.7
• Compiler and version: GCC 6.4.0
• Other relevant information: Relevant netcdf bugs:
  Proposed fix may not work with 4.4.4, see this issue.
  Unable to add _FillValue to INT64 variable Unidata/netcdf-fortran#62
  Upstream netcdf fortran work exposed the bug likely in this PR
  Support 64-bit integer memory type Unidata/netcdf-fortran#190

[rcabell]

NetCDF 4.7.3 is now the default version on Cheyenne, and users are seeing model crashes with it. That may be related to this issue, and/or additional places in the code where it's crashing due to incompatibilities. Adding this here now to bubble up the priority.