Analysis of satellite images shows increasing drought problems

The whole Czech Republic went through one of the driest summer seasons in the recorded history. In August, the temperatures in the South Moravia Region were 3.8°C higher than the average of years from 1981 to 2010 and at the same time the precipitation was 40% below average. High temparatures along with shortage of rainfall have a significant influence on human health and the environment in which we live. The country is changing and is drying out. Analysis of these changes can be done with the help of satellite images.

The European Space Agency (ESA) operates multiple staletites on the Earth’s orbit and as part of the Copernicus programme, satellites called Sentinel take pictures of the Czech Republic in regular intervals (ca. once in 10 days). These images are taken in a multitude of spectral ranges. Because of this, it’s possible to analyze the reflectability of Earth’s surface, which helps us to see changes in vegetation, size of the urban areas, soil humidity and other characteristics.

Below are images from August 2015 and 2018 depicted in natural colours and then in colours of moisture index (combination of NIR and SWIR zones). Based on these images, it’s possible to determine the amount of water in soil.

Even at first sight it seems that there are fields especially in the southeastern part of Brno, which have been significantly affected by the drought. This hypothesis is confirmed when we look at the moisture index map, which indicates the amount of water in soil. Simply put, the darker the colour (blue) is, the more moisture there is in the vegetation. So, it is quite obvious that even when comparing the two driest months of August in the recorded history (2015 and 2018) the amount of water in vegetation this year was dramatically lower.

This decrease in humidity is particulary visible in the southeastern part of Brno and, in general, in areas with flat surfaces and sparse vegetation. Also, after a more thorough examination of these images, a visible reduction of forest vegetation is apparent. The main factor of creation of these clearings is the bark beetle.

And it’s important to note that vegetation serves as a good “defence” of a city against warming of its climate. Especially in the summer season it’s able to effectivelly cool down the urban areas. Occurance of vegetation in the environment changes throughout the year significantly. In the map application, we can see the stretch of the vegetation measured by a so called EVI index (Enhanced Vegetation Index). Values of this index range from -1 to 1, where vegetation has values of 0.2 and above based on its density (amount of biomass). Low values stand for urban areas, bare soil and water (depicted by pink colour). Application was developed in cooperation with Worldfromspace.

In the tray at the bottom, it is possible to change the month and at the top to switch to ZSJ mode (ZSJ in Czech stands for Elementary Residence Unit), where the EVI index calculated for these units.

Sources of data:

Sentinel-Hub

projekt Copernicus

Worldfromspace