Landlab

Landlab - Surface Process Modelling

Quick Reference

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

# Create grid
grid = RasterModelGrid((100, 100), xy_spacing=10.0)
z = grid.add_zeros('topographic__elevation', at='node')
z += np.random.rand(grid.number_of_nodes) * 0.1

# Set boundaries (open bottom edge)
grid.set_closed_boundaries_at_grid_edges(True, True, True, False)

# Create and run components
fa = FlowAccumulator(grid, flow_director='D8')
sp = StreamPowerEroder(grid, K_sp=1e-5)

for _ in range(100):
    fa.run_one_step()
    sp.run_one_step(dt=1000)
    z[grid.core_nodes] += 0.001 * 1000  # Uplift

grid.imshow('topographic__elevation', cmap='terrain')

Grid Types

Key Concepts

Fields and Boundaries

# Fields: data stored at grid elements (nodes, links, cells)
z = grid.add_zeros('topographic__elevation', at='node')
grid.at_node['drainage_area']  # Access existing field

# Boundaries: close all edges except outlet
grid.set_closed_boundaries_at_grid_edges(True, True, True, False)
z[grid.core_nodes] += uplift * dt  # Core nodes exclude boundaries

Essential Operations

Flow Routing

from landlab.components import FlowAccumulator

fa = FlowAccumulator(grid, flow_director='D8')  # or 'Steepest', 'MFD'
fa.run_one_step()
drainage_area = grid.at_node['drainage_area']

Stream Power Erosion

from landlab.components import StreamPowerEroder

sp = StreamPowerEroder(grid, K_sp=1e-5, m_sp=0.5, n_sp=1.0)
sp.run_one_step(dt=1000)  # dt in years

Hillslope Diffusion

from landlab.components import LinearDiffuser

ld = LinearDiffuser(grid, linear_diffusivity=0.01)  # m^2/yr
ld.run_one_step(dt=100)

Load/Save DEM Data

from landlab.io import read_esri_ascii, write_esri_ascii
from landlab.io.netcdf import read_netcdf, write_netcdf

grid, z = read_esri_ascii('dem.asc', name='topographic__elevation')
write_esri_ascii('output.asc', grid, names='topographic__elevation')
write_netcdf('output.nc', grid)  # Save all fields

Multi-Component Model

from landlab import RasterModelGrid
from landlab.components import FlowAccumulator, StreamPowerEroder, LinearDiffuser

grid = RasterModelGrid((100, 100), xy_spacing=100.0)
z = grid.add_zeros('topographic__elevation', at='node')
z += grid.node_y / 1000 + np.random.rand(grid.number_of_nodes) * 0.1
grid.set_closed_boundaries_at_grid_edges(True, True, True, False)

fa = FlowAccumulator(grid, flow_director='D8')
sp = StreamPowerEroder(grid, K_sp=1e-5)
ld = LinearDiffuser(grid, linear_diffusivity=0.01)

dt, uplift_rate = 1000, 0.001
for _ in range(500):
    fa.run_one_step()
    sp.run_one_step(dt)
    ld.run_one_step(dt)
    z[grid.core_nodes] += uplift_rate * dt

When to Use vs Alternatives

Choose Landlab when: You need a modular, component-based framework for landscape evolution modelling that combines multiple surface processes (erosion, diffusion, flow routing, weathering) in a single simulation.

Choose Badlands when: Your focus is on basin-scale landscape evolution with emphasis on sediment transport and stratigraphic architecture.

Choose custom numpy when: You only need a simple 2D diffusion or stream power model without the overhead of a full component framework.

Common Workflows

Landscape Evolution Model with Erosion and Uplift

• Create RasterModelGrid with appropriate dimensions and spacing
• Initialize topographic__elevation field (flat + noise, or load DEM)
• Set boundary conditions (open one edge as outlet, close others)
• Create FlowAccumulator with chosen flow director (D8 or MFD)
• Create StreamPowerEroder with erosion coefficient K_sp
• Create LinearDiffuser for hillslope processes
• Define time step dt and total runtime; choose uplift rate
• Run time loop: flow routing, erosion, diffusion, then uplift
• Save snapshots at intervals with write_netcdf() or write_esri_ascii()
• Visualize final topography with grid.imshow()
• Analyze drainage area and channel profiles
• Extract river long profiles for steepness analysis

Common Issues

Tips

1. Set boundaries first - before adding components
2. Use core_nodes - excludes boundary nodes for operations
3. Check field names - components expect specific names (e.g., 'topographic__elevation')
4. Start simple - add components incrementally and verify each

References

• Components Reference - Available components by category
• Grids Reference - Grid types and configuration

Scripts

• scripts/erosion_model.py - Basic erosion model template