The seasons set the rhythm of life. Living things, including humans, adjust the timing of their annual activities to exploit resources and conditions that fluctuate through the year.

The study of this timing, known as “phenology”, is an age-old form of human observation of nature. But today, we can also watch phenology from space.

With decades-long archives of satellite imagery, we can use computing to better understand seasonal cycles of plant growth. However, methods for doing this are often based on the assumption of simple seasonal cycles and distinct growing seasons.

This works well in much of Europe, North America and other high-latitude places with strong winters. However, this method can struggle in the tropics and in arid regions. Here, satellite-based estimates of plant growth can vary subtly throughout the year, without clear-cut growing seasons.