Mapping agricultural drought in Alberta

agriculture
natural hazards
multispectral
time series
Mapping Alberta’s 2021 and 2023 agricultural droughts with NDVI time series, from province-wide MODIS to daily Planet Fusion data over selected areas, where irrigation largely offset the drought. Published as a two-part blog series.

Mapping Alberta’s 2021 and 2023 agricultural droughts with NDVI time series, from province-wide MODIS to daily Planet Fusion data over selected areas, where irrigation largely offset the drought. Published as a two-part blog series.

Employer: Sparkgeo (internal project)
When: 2023
Data: PlanetScope (Planet Fusion Monitoring), MODIS
Methods: NDVI time series, multi-temporal change analysis
Stack: Python, Xarray, Rasterio, Plotly, Streamlit, Cloud Optimized GeoTIFF (COG), Mapbox, JavaScript

Background

This project used satellite imagery to examine the droughts of 2021 and 2023 in Alberta, both of which were visible in the data. We explored the drought impact using multi-temporal NDVI analysis and visualizations. The project began as an internal demo of Planet Fusion Monitoring, but its main outcome was the drought mapping.

The analysis occurred in two parts, which were presented in two different blog posts. In the first part, low-resolution MODIS data were used to compare NDVI across the entire province over a six-year period, with inter-annual differences displayed in a web map.

Three maps of Alberta. The 2020 and 2023 NDVI maps are mostly green, with the south-east more yellow and orange in 2023. The difference map is mostly pale, with a large red area in the south-east of the province.

MODIS NDVI across Alberta in 2020 (left) and 2023 (centre), and the difference between them (right), where red marks lower NDVI in 2023. The largest drop is in the south-east, around Calgary, Lethbridge and Medicine Hat. From the web map in part 1.

The second part of the project used Planet Fusion Monitoring, an analysis-ready data product from Planet. For this stage, areas of interest (AOIs) across Alberta agricultural zones were selected, and Planet Fusion data was used to produce daily NDVI time series plots and animated visualizations. An interactive dashboard was created to explore the results, allowing users to switch between the AOIs and compare the time series plots and animations for each.

Two line charts from April to October. Top: NDVI peaks in July; 2019 stays highest through late summer, while 2021 and 2023 fall below the average from July. Bottom: 2019 sits up to 0.15 above average in August, 2021 drops to about 0.2 below average in early August, and 2023 about 0.1 below.

Daily Planet Fusion NDVI for a dryland AOI near Calgary, comparing 2019 (a wet year) with the 2021 and 2023 droughts and the average (top), and each year’s difference from the average (bottom). From part 2.

My contribution

  • Developed a workflow to retrieve and process MODIS and Planet Fusion datasets into NDVI time series and change layers.
  • Produced an interactive web map to compare inter-annual MODIS NDVI data.
  • Produced a dashboard and interactive visualizations for the Planet Fusion Monitoring blog.
  • Wrote, edited and published both blog posts.

Outcome

Daily Planet Fusion NDVI over irrigated and dryland fields near Lethbridge through the growing season, 2020 (left) and 2023 (right). In 2023 the irrigated fields, including the circular centre-pivot fields, stay green, while the dryland fields drop off sharply. From part 2.
  • Analysis from this work demonstrated the utility of satellite image data for mapping drought conditions, and particularly the ability of Planet Fusion to produce smooth, gap-free daily time series to help illustrate the impact.
  • Drought impacts were worst in 2021 and 2023, as expected, but their extent varied across the province, and irrigation largely mitigated the impact.
  • Results presented in a two-part blog series, with the interactive web map and dashboard embedded in the posts. The dashboard is no longer online.