drought-monitoring 0.1.4

Composite Drought Index via GEE + COG output + climate-science plots

drought-monitoring

A Python package for computing the Composite Drought Index (CDI) over 20–30 year monitoring periods using Google Earth Engine, with in-memory dask-parallelised spatial computation, Cloud Optimized GeoTIFF export, and publication-quality climate science visualisations.

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Installation

# pip
pip install drought-monitoring

# uv
uv add drought-monitoring

# with all optional dependencies (GEE + COG + plots)
pip install "drought-monitoring[all]"

Optional extras:

Extra	Installs	Use for
gee	earthengine-api	fetching GEE data
cog	rasterio, rioxarray	COG export / import
plot	matplotlib	visualisation
all	all of the above	full workflow

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Package structure

drought_monitoring/
├── core.py      CDI mathematics on pd.Series
├── spatial.py   pixel-wise computation on xr.DataArray (dask-parallelised)
├── gee.py       GEE authentication + ERA5-Land / MODIS xee cube fetching
├── io.py        Cloud Optimized GeoTIFF (COG) export and import
└── plot.py      publication-quality climate science figures
tests/
└── test_core.py
pyproject.toml
README.md

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Typical Jupyter notebook workflow

1. Authenticate GEE

from drought_monitoring.gee import authenticate
authenticate(project="my-gee-project")   # opens browser on first use

2. Generate yearly drought maps (full in-memory pipeline)

from drought_monitoring.gee import yearly_drought_maps

aoi = [38.0, 3.5, 42.5, 7.0]   # [lon_min, lat_min, lon_max, lat_max]
                                  # Borena region, Southern Ethiopia

# Streams ERA5 + MODIS via xee, computes CDI pixel-wise with dask,
# resamples to annual means — nothing written to disk
ds = yearly_drought_maps(aoi, start_year=2000, end_year=2020)
# xr.Dataset with variables: PDI, TDI, VDI, CDI
# dims: (year, latitude, longitude)

3. Plot all years

ds["CDI"].plot(col="time", col_wrap=4, cmap="RdBu", robust=True, figsize=(20, 14))

4. Export to Cloud Optimized GeoTIFFs

from drought_monitoring.io import cdi_stack_to_cog

paths = cdi_stack_to_cog(ds, output_dir="outputs/", prefix="Borena_2000_2020")
# outputs/Borena_2000_2020_PDI.tif
# outputs/Borena_2000_2020_TDI.tif
# outputs/Borena_2000_2020_VDI.tif
# outputs/Borena_2000_2020_CDI.tif

5. Visualise COGs interactively

import leafmap

m = leafmap.Map(center=[5.0, 40.0], zoom=6)
m.add_cog_layer("outputs/Borena_2000_2020_CDI.tif", name="CDI")
m

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Area-averaged time series workflow

For a single-pixel or spatially-averaged CDI time series:

from drought_monitoring.gee import fetch_era5_precip, fetch_era5_temp, fetch_modis_ndvi
from drought_monitoring import compute_all
from drought_monitoring.plot import plot_timeseries, plot_anomaly_bars

precip = fetch_era5_precip(aoi, start_year=2000, end_year=2020)
temp   = fetch_era5_temp(aoi,   start_year=2000, end_year=2020)
ndvi   = fetch_modis_ndvi(aoi,  start_year=2000, end_year=2020)

df = compute_all(precip, temp, ndvi, window=3)
# pd.DataFrame with columns: PDI, TDI, VDI, CDI

fig = plot_timeseries(df, title="CDI — Borena Region",
                      subtitle="ERA5-Land + MODIS MOD13A3  |  2000–2020")
fig.savefig("CDI_timeseries.png", dpi=300, bbox_inches="tight")

fig2 = plot_anomaly_bars(df, title="Annual Mean CDI Anomaly")
fig2.savefig("CDI_annual.png", dpi=300, bbox_inches="tight")

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Data sources

Variable	GEE collection	Band	Units
Precipitation	ECMWF/ERA5_LAND/MONTHLY_AGGR	total_precipitation_sum	mm month⁻¹
Temperature	ECMWF/ERA5_LAND/MONTHLY_AGGR	temperature_2m	°C
NDVI	MODIS/061/MOD13A3	NDVI	[−1, 1]

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CDI formula

Each sub-index follows Burchard-Levine et al. (2024):

DI = (μ_IP / μ_LTM) × sqrt(RL_IP / RL_LTM)

CDI = 0.50 × PDI + 0.25 × TDI + 0.25 × VDI

Symbol	Meaning
μ_IP	Trailing rolling mean over the interest period (default 3 months)
μ_LTM	Long-term mean of μ_IP for that calendar month
RL_IP	Count of months inside the IP where the anomaly condition holds
RL_LTM	Long-term mean of RL_IP for that calendar month

PDI & VDI use deficit streaks (raw < monthly LTM). TDI uses excess streaks (raw > monthly LTM).

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CDI severity classes

CDI value	Class
< 0.50	Extreme drought
0.50 – 0.65	Severe drought
0.65 – 0.80	Moderate drought
0.80 – 0.90	Mild drought
0.90 – 1.10	Near normal
1.10 – 1.20	Mild wet
1.20 – 1.30	Moderately wet
> 1.30	Very wet

Values < 1 indicate drought; values ≈ 1 are near-normal; values > 1 are wetter than normal.

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Monitoring period

Default	Minimum	Maximum
20 years	20 years	30 years

An error is raised if the requested period is outside this range.

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COG structure

Each output GeoTIFF contains one band per timestep. Band descriptions are ISO-8601 date strings (YYYY-MM or YYYY), so every file is self-documenting and can be range-requested from cloud storage (S3, GCS, Azure Blob) by leafmap, QGIS, or any GDAL tool.

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Running tests

pytest tests/ -v

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Reference

Based on: Burchard-Levine, V. et al. (2024). pyCDI: a Python implementation of the composite drought index. EO-Africa R&D, ESA. https://github.com/VicenteBurchard/pyCDI