Preparation dem.asc and latlon.nc

[9202014710]

I'm preparing the dem.asc and latlon.nc.
For dem.asc, the data was below, which was float rather than int as showed in the test file, if it's OK that the number was float. The dem.asc was gotten by Arcgis.
xllcorner 113.67603569604
yllcorner 27.918669336457
cellsize 0.00011268696206158

Another question is why there are 3 layers of latlon.nc. xc_l0 and yc_l0 is for morph, xc and yc is for meteo, how about the xc_l11 and yc_l11? How to get a latlon.nc by the available data.

[9202014710]

And I confused about "resolution hydrology = 24000" of the test domain, how was this number calculated.

[rohinikumar82]

1. It is OK - the number can be given in float.
2. xc_l11 and yc_l11 is for the Level 11 data. You can use any program (python, R or matlab) to create latlon.nc file. There may be a preprocessing script within the mHM codebase to create such latlon.nc file.
3. resolution hydrology = 24000 is a test example. This corresponds to the spatial resolution of 24 km.

[9202014710]

Thanks for your reply, I have learned how to get latlon.nc by using the provided program in python.
However, for asc files obtained in WGS84 coordinate system, cellsize is expressed in degrees (cellsize 0.00011268696206158), how should we calculate resolution? Because the correct resolution could not be entered, the mHM calculation could not be performed properly.
For the test file, it looks like the formula is: 24000 = 68500.

[9202014710]

Thanks for your reply, I have learned how to get latlon.nc by using the provided program in python.
However, for asc files obtained in WGS84 coordinate system, cellsize is expressed in degrees (cellsize 0.00011268696206158), how should we calculate resolution? Because the correct resolution could not be entered, the mHM calculation could not be performed properly.
For the test file, it looks like the formula is: 24000 = 68500.

[pallavhydro]

Hi @9202014710

Good to know you made progress with generating the latlon file. Nice.

Few comments here:

1. mHM has 4x resolutions.
   L0 (or xc_l0, yc_l0 in latlon file)
   L1 (or xc_l1, yc_l1 in latlon file)
   L11 (or xc_l11, yc_l11 in latlon file)
   L2 (not needed in latlon file)

2. Meaning of the mHM resolutions
   L0 is the fine scale, morphology resolution like dem, LAI, etc.
   L2 is the coarse scale, meteorology resolution of pre.nc, etc.
   L1 is the model scale, hydrology resolution which will be the resolution of mhm output on water balance components
   L11 is the second model scale, routing resolution, which will be the resolution of the mhm output on routed streamflow/discharge
   We usually keep L1 = L11 for simplicity, and would suggest the same for you.

3. Usually resolutions of input data are such that L0 data is in sub kilometre, and L2 is in kilometres. mHM facilitates such that you can model at a resolution between L0 and L2. Some used examples could be
   L0 = 200 m
   L2 = 24 km
   L1 = 2 km
   or
   L0 = 200 m
   L2 = 24 km
   L1 = 24 km
   We rarely use L1 = L0 because, first, that is inefficient due to large runtime, second, mHM already considers the L0 details even while running in coarse resolution (magic of mHM! hint: read papers on multi scale parameter regionalisation, MPR)

4. Coming back to the second part of your question, the decimal model resolution (hydrology and routing) can be entered as e.g. 0.25 degrees as well. Just make sure you select correct iFlag_cordinate_sys in mhm.nml. This information is clearly included in the comments in mhm.nml. (suggestion: reading the comments of .nml flies helps a lot while learning mHM)

!> resolution of Level-1 hydrological simulations in mHM [m or degree] per domain
!> NOTE: if iFlag_cordinate_sys = 0, then resolution_Hydrology is in [m]
!>       if iFlag_cordinate_sys = 1, then resolution_Hydrology is in [degree-decimal]

I hope this information helps. All the best!

Pallav

[9202014710]

Thanks so much for your reply, your comments have been very helpful to me.
But there is one thing that confuses me: how can I determine the resolution values of L0, L2, and L1? As you can see, when using WGS 84, the cell size is typically represented by a decimal number rather than an integer value.

[9202014710]

Can I get this resolution data with Arcgis, or is there a program that can read it directly?

[pallavhydro]

Hi @9202014710

I guess I should have provided an example with decimal degrees for the resolutions. E.g.
L0 = 0.001953125 (1/512 or 1/ 2^9 degree)
L2 = 0.25 (1/4 or 1/ 2^2 degree)
L1' = L11` = 0.125 (1/8 or 1/ 2^3 degree)

Thus with iFlag_cordinate_sys = 1 you can enter integer or decimal values for L1 and L11 in mhm.nml.

Just keep in mind that mHM behaves the best in systems where L2 is a multiple of L1 (and L11) which in turn is a multiple of L0, as in the above example. E.g. 0.001953125 x 64 = 0.125 and 0.125 x 2 = 0.25.

In your case, L0 = 0.00011268696206158 which can be a bit hard to work with. Perhaps converting it into a nearby resolution of 1/(2^n) might help, assuming that the resolution of your meteorology (L2) is a factor of 1 degree (e.g. 0.25, 0.125, etc.).

Pallav

[9202014710]

The example files I see are all integers...
What is the relationship between this resolution and cellsize? I always thought there was some kind of multiple relationship.
L0 = 0.00011268696206158 is the content of dem.asc in the research area I obtained, and the resolution seems to be 30m. Maybe I should resample it with gis to meet what you said above?

[pallavhydro]

In the context of mHM, resolution, cell size, grid size, pixel size, are all one and the same. However, if you are using iFlag_cordinate_sys = 1, then the resolution should be in latlon, decimal degree system (without projections). And if you are using iFlag_cordinate_sys = 0 then the resolution should be in meters (projected system).

Yes resampling could be a way forward

Notes:

1. All L0 data (morph, LAI) need to be in the same resolution.
2. The extent of all input data (L0 and L2) should also match.

[9202014710]

Allow me to confirm with you that the resolution refer to cellsize.

[9202014710]

Hi, I modified the resolution to float, what's the following error means?
"
Read data ...
Reading data ...
Reading dem and lcover ...
Reading dem for domain: 1 ...
Reading lcover for domain: 1 ...
Reading data for domain: 1 ...
Reading slope ...
Reading aspect ...
Reading soil ids ...
Reading LAI ...
Reading latitude/logitude ...
in 0.088 seconds.
in 0.123 seconds.
***WARNING: Geological unit 5
is not appearing in study domain.
***WARNING: Geological unit 6
is not appearing in study domain.
***WARNING: Geological unit 8
is not appearing in study domain.
in 0.123 seconds.
Initialize domains ...
***ERROR: subroutine mo_read_latlon: size mismatch in latlon file for level1 in domain 1!
Latitude expected to have following dimensions ... rows:1, cols:1
Latitude provided ... rows:6, cols:9
1
"

[BryanSouzaM]

The latlon file does not match the hydrology resolution.

[9202014710]

Thanks for the reply.
This error is because the inconsistent resolution of luse/*.asc. And I have solved the problem.

[9202014710]

But here arises a new problem.
“”“

of domains: 1

Given data directories:

  DOMAIN                    1

---

Morphological directory:      input/morph (found)
Land cover directory:         input/luse (found)
Level-2 header directory:     input/meteo/pre (found)
Precipitation directory:      input/meteo/pre (found)
Temperature directory:        input/meteo/tavg (found)
PET directory:                input/meteo/pet (found)
Output directory:             output_b1 (found)

Read data ...
Reading data ...
Reading dem and lcover ...
Reading dem for domain: 1 ...
Reading lcover for domain: 1 ...
Reading data for domain: 1 ...
Reading slope ...
Reading aspect ...
Reading soil ids ...
Reading LAI ...
Reading latitude/logitude ...
in 0.092 seconds.
in 0.138 seconds.
***WARNING: Geological unit 5
is not appearing in study domain.
***WARNING: Geological unit 6
is not appearing in study domain.
***WARNING: Geological unit 8
is not appearing in study domain.
in 0.138 seconds.
Initialize domains ...
***ERROR: Two resolutions size do not confirm: 10
1
”“”
What's the error means? And how can I solve the problem?

[9202014710]

Wow! The good news here is that I have successfully run mhm model based on decimal degrees data.
First of all, thanks for mHM team's help.

I changed the file in test_domain accordingly. For example, change the information about *.asc to the following:
ncols 288
nrows 432
xllcorner 113
yllcorner 27
cellsize 0.01171875
The biggest change is that the xllcorner, yllcorner and cellsize have been modified in the form of decimal degrees. Other files have also been modified accordingly.

But there's one thing still confuses me. How to get the value of resolution_Hydrology?
It seems that there is a multiple relationship between resolution and cellsize, ncols, and nrows.
For example, 24000 = 6 * (9-1) * 500, which represents resolution_Hydrology = ncols * (nrows - 1) * cellsize.
When I set another value, there would be an error:
"***ERROR: Two resolutions size do not confirm: 10"
I'm not sure if this relationship exists, or it's just a coincidence. If the relationship exists, what does this formula mean? Why is it "nrows - 1" rather than "nrows"?