Weather radars used to count flying insects

Weather radar to count flying insects Keystone-SDA

Swiss and American researchers have used weather radar data to estimate the number of insects flying in the skies over the United States. This method should help reveal historical changes in insect fauna.

A researcher from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and two American colleagues used data from 140 weather radars in the United States, the WSL explained on Monday. According to the authors, some 100,000 billion insects fly through the American skies on an average summer’s day.

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Until now, insect monitoring has been limited to a few species and locations. Weather radar offers an automated, inexpensive and large-scale method of monitoring insect populations in the air: algorithms can filter out signals from insects whose trajectories leave typical tracks on radar images.

In the United States, this data is freely accessible. The researchers’ observations make the continental patterns of flying insects visible for the first time, and provide a unique time series over the ten years evaluated (2012 to 2021).

However, the method is difficult to apply in Switzerland. In Switzerland, many weather radars are installed on ridges or mountain peaks, so flying insects literally fly under the radar.

Combining sources

While the number of insects in the United States appears to be stable overall over the period observed, there are significant fluctuations at regional level. These variations are mainly linked to winter temperatures: insect populations have fallen the most in regions where winter temperatures have risen.

Studies carried out on the ground show that it is mainly rare species or species sensitive to environmental changes that disappear, while common insect species multiply. It is therefore important to combine radar data with other data sources.

For the researchers, it is also likely that the steepest decline in insect populations occurred in the 1970s and 1990s, i.e. before the period of observation. But they are convinced that weather radar can provide valuable baseline data on which future time series can be based. Their work has been published in the journal Global Change Biology.

Adapted from French by DeepL/ac

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