author: "Rafael Schouten" title: "Dispersal.jl example" –-

Dispersal simulations

In this example we will run a simulation of the spread of an invasive insect accross Australia, after an incursion in Brisbane.


First, load the required packages. Dates is a core julia package that give us date/time handling, GeoData and RasterDataSources simplify the loading of geospatial raster files. It requires also loading NCDatasets.jl and ArchGDAL.jl to load NetCDF and GeoTiff files, respectively.

using DynamicGrids
using GeoData, NCDatasets, ArchGDAL, RasterDataSources
using Dispersal, Dates, Plots, GrowthMaps, Unitful, Statistics
using Unitful: °C, K, cal, mol, mm
basedir = realpath(joinpath(dirname(Base.pathof(Dispersal)), "../docs"))

Define simulation extent in space and time:

We use DateTime of for the time dimension:

timestep = Month(1);
tspan = DateTime(2022, 1):timestep:DateTime(2030, 12)
aust = Lon(Between(113, 154)),
       Lat(Between(-45, -10));

Define a RuleSet: climate driven population growth

This will involve combining multiple dispersal components into a single RuleSet object: population growth, local dispersal, Allee effects, and human dispersal.

Local dispersal

localdisp = InwardsDispersal(;
    formulation=ExponentialKernel(; λ = 0.0125),

Allee effects

allee = AlleeExtinction(; minfounders=10.0);

Human dispersal

The human dispersal component is generated from an array or population data. First we'll open an input tiff, and move it to a memory backed GeoArray.

humanpop_url = ""
humanpop_filename = "population_density.tif"
humanpop_filepath = joinpath(basedir, humanpop_filename)
isfile(humanpop_filepath) || download(humanpop_url, humanpop_filepath);

Again select the Australian bounds. This time we also select the first Band. Tiff data always has bands, even when there is only one:

humanpop = GDALarray(humanpop_filepath; mappedcrs=EPSG(4326))[Band(1), aust...] |>
    A -> replace_missing(A, missing) |>
    A -> permutedims(A, (Lat, Lon)) |> 
    A -> reorder(A, Lat=ReverseArray, Lon=ForwardArray)
savefig(joinpath(basedir, "build/assets/humanpop.png"));


humandisp = HumanDispersal(

To obtain spatially and temporally heterogeneous growth rates for our growth model, we simplify the examples tutorial over at GrowthRates.jl.

# Generate a growth response curve
p = 3.626804f-01
ΔH_A = 3.586625f4cal/mol
ΔH_H = 1.431237f5cal/mol
Thalf_H = 2.988454f2K
ΔH_L = -1.108988f5cal/mol
Thalf_L = 2.459949f2K
T_ref = K(25.0f0°C)
growthresponse = Layer(:tavg, °C,
    SchoolfieldIntrinsicGrowth(p, ΔH_A, ΔH_L, Thalf_L, ΔH_H, Thalf_H, T_ref)
# Add some lower and upper temperature bounds that cause mortality
coldthresh = -10.0f0°C |> K
coldmort = -log(1.23f0)K^-1
heatthresh = 30.0f0°C |> K
heatmort = -log(1.15f0)K^-1
coldstress = Layer(:tavg, °C, LowerStress(coldthresh, coldmort))
heatstress = Layer(:tavg, °C, UpperStress(heatthresh, heatmort))
# Set a stressor based on precipitation - there are better data to use
# for this, but this is easy to download for the example
wetthresh = 40mm
wetmort = -0.01f0mm^-1
wetstress = Layer(:prec, mm, LowerStress(wetthresh, wetmort))
# Define the whole model
model = growthresponse, coldstress, heatstress, wetstress

# Download some climate data, and reseample to match the population data
ser = map(series(WorldClim{Climate}, (:tavg, :prec); month=1:12)) do stack
    map(A -> resample(A, humanpop), stack)
growthrates = mapgrowth(model; series=ser, tspan=1:12)

Plot the growth layer:

mode_ = Projected(; crs=crs(growthrates), mappedcrs=EPSG(4326))
growthrates = set(growthrates[Band(1)], Lat=mode_, Lon=mode_) |>
    A -> set(A, Ti(DateTime(2017, 1):Month(1):DateTime(2017, 12))) |>
    A -> permutedims(A, (Lat, Lon, Ti)) |>
    A -> reorder(A, Lat=ReverseArray, Lon=ForwardArray)
plot(growthrates[Ti(5)]; clims=(0, 0.1))
Plots.savefig(joinpath(basedir, "build/assets/growthrates.png"));


Create a ExactLogisticGrowthMap rule from the layer, here we use unitful units for the layers' time dimension:

carrycap = 1e9
growth = LogisticGrowth(; rate=Aux(:growthrates), timestep=Day(1), carrycap=carrycap);

Define initialisation data

Make a zeros GeoArray. We need to replace the missing values, as init can't contain missing or it will spread everywhere. We then initialise a population in Brisbane:

init = replace_missing(humanpop, NaN) |> zero
lat, lon = -27.5, 153 # Brisbane
init[Lat(Contains(lat)), Lon(Contains(lon))] = carrycap

Define a masking layer

This layer lets the simulation know which cells should be ignored.

masklayer = boolmask(growthrates[Ti(1)])
savefig(joinpath(basedir, "build/assets/mask.png"));


Define a combined ruleset

ruleset = Ruleset(humandisp, localdisp, allee, growth; timestep=timestep)


Outputs hold all spatial and temporal information about the simulation, as these match the size and length of the output, making the Ruleset independent of location and time. init, tspan, aux and mask are common to all outputs, here we use the masklayer for mask and growthrates for aux.

Gif files are an easy way to share the visual dynamics of the simulation. GifOutput saves a gif when the simulation finishes.

You can use the built-in Greyscale scheme or any scheme from ColorSchemes.jl.

using ColorSchemes
output = GifOutput(init;
    # Core keywords
    # Visualisation keywords, fps=10,
    minval=0.0, maxval=carrycap, 
    filename=joinpath(basedir, "build/assets/sim.gif"),

Run a simulation and save a gif

To run a simulation, we pass in the output and rulset.

sim!(output, ruleset);

Drosphila suzukii spread

Live simulation outputs

There are a number of live outputs provided in DynamicGrids.jl and specific output packages DynamicGridsGtk and DynamicGridsInteract that keep heavy graphics and web dependencies separate form the rest of the framework.

REPL output

You can view a simulation over SSH or just in your local console using the included REPLOutput. It doesn't work so well in Atom/Juno, so we only recommend using it in a real terminal. It also works better in a terminal where you can easily reduce the font size.

using Crayons
output = REPLOutput(init; 
    style=Block(), fps=5, color=:white, store=false
sim!(output, ruleset);

The Braile() style uses half the space of the Block() style, but won't look as clear.

Interactive web outputs

DynamicGridsInteract.jl produces interactive web page outputs for a simulation. It uses Interact.jl for live control, providing a control console and sliders for model parameters, even for your own custom models.

The simple InteractOutput() is the core output that can run on its own inside Juno or a Jupyter notebook. It can also be served to a browser locally or over the web using ServerOutput(), or run in a standalone desktop app using ElectronOutput().

Juno or jupyter notebooks

Building a InteractOutput() and running display() will open an output in a plot pane in Juno. See the example above to define an image processor. Setting store to true will save the last simulation to the output array to be saved or converted to a gif. Really long simulations may use your avilable ram, in which case set store to false.

using DynamicGridsInteract
output = InteractOutput(init;
    tspan=tspan, mask=masklayer, aux=(growthrates=growthrates,),
    fps=10, store=true,, 
    minval=0.0, maxval=carrycap,

Wrap the IneractOutput in a standalone desktop (electron) app

This will create a standalone desktop app wrapping the InteractOutput. Unfortunately the compile and load time for electron can take quite a while.

output = ElectronOutput(init;
    tspan=tspan, mask=masklayer, aux=(growthrates=growthrates,),
    fps=10, store=true,, 
    minval=0.0, maxval=carrycap,

Serving web pages

The InteractOutput can be served locally or over the web. You may need to do some port or firewall configuration on your server, but otherwise this is all you need to do to serve a simulation. Unlike other outputs, ServerOutput makes a copy of the internal InteractOutput for each new connection. Changes in one connection will not effect anything in the others. It tends to flash in Firefox, Chrome may be a better option.

output = ServerOutput(init;
    tspan=tspan, mask=masklayer, aux=(growthrates=growthrates,),
    fps=10, store=true,, 
    minval=0.0, maxval=carrycap,

Run in a GTK window

The GTKOutput in DynamicGridsGtk.jl is a simple desktop output that just shows the simulation without controls. It can be useful for faster load-time than ElectronOutput, and also dedicates all screenspace to viewing the simulation.

using DynamicGridsGtk
output = GtkOutput(init;
    mask=masklayer, aux=(growthrates=growthrates,), tspan=tspan,
    fps=10, store=true,, 
    minval=0.0, maxval=carrycap,
sim!(output, ruleset)