Some question about FlowAccumulator, StreamPowerEroder and LinearDiffuser

[kookil]

I am using real terrain and precipitation to calculate soil erosion and sediment transport by landlab. And here is part of my code.
(mg, z) = read_esri_ascii(path, name="topographic__elevation") fr = FlowAccumulator(mg) Q = mg.at_node['surface_water__discharge'] ld = LinearDiffuser(mg, linear_diffusivity=0.0001) sp = StreamPowerEroder(mg, K_sp=1., sp_type='Unit', a_sp=1., b_sp=0.5, c_sp=1., use_Q=Q)
The problem I'm having is as follows:

1. Because I want to change the runoff, so I add
   runoff_rate = np.arange(mg.number_of_nodes, dtype=float) rnff = mg.add_field(" water__unit_flux_in ", runoff_rate, at=" node", clobber=True)
   like the document, but I find the result mg.at_node['surface_water__discharge'] does not change, and I can't find the reason;

2. I follow the method StreamPowerEroder in landlab to add existing precipitation values in use_Q, but the code reports an error that there is no use_Q in the function, is this a version problem? my landlab version is 2.2.0;

3. The grid data I am using has several thousand rows and columns, and I run LinerDiffuser for many days without results, is this because the number of data is too large?

I would be grateful if you can give any assistance.

[mcflugen]

@kookil Thank you for your interest in landlab!

1. Could you please provide a link to the document you are referring to? In your sample code you use " water__unit_flux_in " and " node". Are those extra spaces just typos introduced when you made this issue or are they also in the code you are trying to run? The spaces would definitely result in unexpected behavior.
2. It looks like the use_Q keyword was removed from the StreamPowerEroder several years ago when we moved from version 1 to 2. I wonder if you are following old documentation?
3. Yes, it could definitely be the case that your grid is too large for the LinearDiffuser. If this poses a problem for you, we could look into speeding it up.

[kookil]

Thank you for your help. With your help, I solved part of the problem. After re-reading the official documentation, I found that the existing version does not have use_Q, so I modified the previous code. But when using the latest StreamPowerEroder I encountered a similar problem to the first question, which is the part of the code you wish I could provide.  The documentation mentions "The default is to use the grid field 'drainage_area'. To use custom spatially/temporally varying rainfall, use 'water__unit_flux_in' to specify water input to the FlowAccumulator and use "surface_water__discharge" for this keyword argument." To control the runoff, I used the following code: mg=RasterModelGrid((9,9)) _=mg.add_field('topographic__elevation',mg.node_x**0.5+mg.node_y**2,at='node') for edge in (mg.nodes_at_left_edge, mg.nodes_at_right_edge):     mg.status_at_node[edge] = mg.BC_NODE_IS_FIXED_VALUE for edge in (mg.nodes_at_top_edge, mg.nodes_at_bottom_edge):     mg.status_at_node[edge] = mg.BC_NODE_IS_CLOSED lst = random.random(size=(9,9)) mg.at_node['water__unit_flux_in'] = lst fr = FlowAccumulator(mg, flow_director='D8') sp = StreamPowerEroder(      mg,      K_sp=1.,      sp_type='Unit',      a_sp=1.,      b_sp=0.5,      c_sp=1.,      discharge_field='surface_water__discharge') fr.run_one_step() sp.run_one_step(1.) But no matter how lst changes, the final topographic__elevation value is fixed. I still don't understand why the result is always fixed, I hope you can answer my doubts.

[mcflugen]

@kookil In the future, if possible, please reply to GitHub issues through the website rather than by email as GitHub doesn't properly format the emails.

I'm having trouble reproducing your problem. If I run the following code, which I think is what you are also using, the resulting mg.at_node["topographic__elevation"] is different from its initial value. If I then rerun the code with a different random value of lst, I get a different value for the elevations.

import numpy as np
from numpy import random
from landlab import RasterModelGrid
from landlab.components import FlowAccumulator, StreamPowerEroder

mg = RasterModelGrid((9, 9))
mg.add_field('topographic__elevation', mg.node_x**0.5 + mg.node_y**2, at='node')

for edge in (mg.nodes_at_left_edge, mg.nodes_at_right_edge):
    mg.status_at_node[edge] = mg.BC_NODE_IS_FIXED_VALUE
for edge in (mg.nodes_at_top_edge, mg.nodes_at_bottom_edge):
    mg.status_at_node[edge] = mg.BC_NODE_IS_CLOSED

lst = random.random(size=(9,9))
mg.at_node['water__unit_flux_in'] = lst
fr = FlowAccumulator(mg, flow_director='D8')

z_initial = mg.at_node["topographic__elevation"].copy()

sp = StreamPowerEroder(
    mg,
    K_sp=1.,
    sp_type='Unit',
    a_sp=1.,
    b_sp=0.5,
    c_sp=1.,
    discharge_field='surface_water__discharge'
)

fr.run_one_step()
sp.run_one_step(1.)

assert not np.allcose(z_initial, mg.at_node["topographic__elevation"])

Are you doing something differently? Or perhaps I misunderstand what you are expecting?

[kookil]

I'm sorry for the inconvenience caused by replying by mail earlier.
And I'm surprised that you run my code and get different elevation values ​​because that's exactly what I want. Maybe I'm doing something wrong somewhere else. Thanks for being able to solve my problem!

[mcflugen]

@kookil Could you please paste a minimal code example that demonstrates the issue you are seeing?