Objective and Background


The central objective of the GrowApp is to document, analyze, visualize and communicate climate and human induced changes in our environment via mobile phones.

The GrowApp allows you to animate seasonality in your environment by regularly making photos of trees, gardens and landscapes from exactly the same position. The photos are converted into animations. People can jointly make animations. GrowApp helps to track the climate change induced lengthening of the growing season and is part of the worldwide GLOBE science education program.

Seasonal changes

Our environment is continuously changing. If you look back to photos taken a few years ago you already notice how old-fashioned people, cars and our whole environment looked like. Also our natural environment is continuously changing because of changing weather conditions throughout the year. Most obvious are the seasonal changes. The never ending cycle of spring, summer, autumn and winter are accompanied by phenological events like leaf unfolding, flowering, fruit ripening, autumn coloring and leaf fall. These phenological events significantly determine how our environment looks like.

Phenological observations

The timing of the phenological events varies strongly from year to year. After warm winters trees unfold their leaves weeks earlier compared to a cold spring. Temperature is one of the main factors influencing the timing. We tend to normally forget when what happens in our environment unless we write it down or when we connect a special yearly recurring event like our birthday to an event taking place in nature like the flowering of horse chestnut. Because of the visibility of phenological events, people like to record it, year after year. The oldest phenological observations go back to the year 846 when the start of flowering of cherry trees were written down.

The increase in temperature in the past decades has changed the timing of phenological events. Scientists have been able to show this climate change impact signal by using millions of phenological observations. The problem with phenological observations is that it is time consuming to do the observations and that only a relative small number of species and a small number of individuals per species are recorded.


With the introduction of satellites it became possible to record the green-wave by measuring the greenness of the whole land cover. For every block of 25 by 25 or even 5 by 5 meter greenness data is available when the satellite comes over and when it is not cloudy. However, it still is not possible to identify the species that is photographed from space and the frequency of the pictures is a problem.