THEME: FLOODS AND DROUGHTS - Copernicus Browser

 THEME: FLOODS AND DROUGHTS

                                                              SATELLITE: Sentinel-2 L2A

INDEX: True color

IMAGES:

SUBJECT ANALYTICALLY:

This optimized True color script uses the visible light bands red, green and blue in the corresponding red, green and blue color channels, resulting in a product with natural colours that represents the Earth as humans would naturally see it. The visualisation uses highlight compression and improves the contrast and color vividness through minor contrast and saturation enhancement.

COMMENTS – OBSERVATION:

In the left image we can see areas depicted in dark brown, in December 2016, these are areas with abundant drought. In contrast, in the right image, in December 2024 respectively, the areas that had suffered this devastating fire appear to be now overgrown.

 

INDEX: Moisture Index

Normalized Difference Moisture Index (NDMI)

IMAGES:

SUBJECT ANALYTICALLY:

The normalized difference moisture Index (NDMI) is used to determine vegetation water content and monitor droughts. The value range of the NDMI is -1 to 1. Negative values of NDMI (values approaching -1) correspond to barren soil. Values around zero (-0.2 to 0.4) generally correspond to water stress. High, positive values represent high canopy without water stress (approximately 0.4 to 1). 

COMMENTS – OBSERVATION:

In the left image, December 2016, it is easily understood that in the burned areas, there is intense drought, due to high temperatures and minimal rainfall. Thus, the burned areas appear in an orange-red color.

While, in the right image, in the same month of 2024, the same areas have returned to their natural levels. This is understood based on the image, since the majority of the areas are depicted in blue.

 

INDEX: NDWI

SUBJECT: Normalized Difference Water Index (NDWI)

IMAGES: 

SUBJECT ANALYTICALLY:

The normalized difference water index is most appropriate for water body mapping. Values of water bodies are larger than 0.5. Vegetation has smaller values. Built-up features have positive values between zero and 0.2.

COMMENTS – OBSERVATION:

In the left image, we can see embedded features in the areas that have suffered fire. In December 2016, these appear with an index less than 0.2 and greater than 0 and are depicted in the images with very light shades of green.

In contrast, in the right image, December 2024, the burned areas have returned to their natural vegetation.

 

INDEX: NDMI

SUBJECT : NDMI for Moisture Stress

IMAGES:

SUBJECT ANALYTICALLY:

The Normalized Difference Moisture Index (NDMI) for moisture stress can be used to detect irrigation. For all the index values above 0, knowing the land use and land cover, it is possible to determine whether irrigation has taken place. Knowing the type of crop grown (e.g. citrus crops), it is possible to identify whether irrigation is being effective or not during the crucial growing summer season, as well as find out if some parts of the farm are being under or over-irrigated.

COMMENTS – OBSERVATION:

In the left image, we can see areas that have suffered fires. In December 2016, these appear with an index above 0 and are depicted in white in the images, due to the low humidity index and the lack of irrigation.

In contrast, in the right image, December 2024, there is a uniform image on the island. More specifically, there are not such great contrasts of blue-white colors, but the island is depicted all in shades of blue.

 

INDEX: NDVI

Subject: Normalized Difference Vegetation Index (NDVI)

IMAGES: 

SUBJECT ANALYTICALLY:

The normalized difference vegetation index is a simple, but effective index for quantifying green vegetation. It is a measure of the state of vegetation health based on how plants reflect light at certain wavelengths. The value range of the NDVI is -1 to 1. Negative values of NDVI (values approaching -1) correspond to water. Values close to zero (-0.1to 0.1) generally correspond to barren areas of rock, sand, or snow. Low, positive values represent shrub and grassland (approximately 0.2 to 0.4), while high values indicate temperate and tropical rainforests (values approaching 1).

COMMENTS – OBSERVATION:

In the left image, in December 2016, the burned areas are distinguished with a light green, due to the minimal vegetation, due to the devastating fire a few months ago.

In contrast, in the right image, in December 2024, an intense green color is observed almost throughout Thassos. Thus, we understand that there is reforestation in the burned areas.

 

INDEX: SWIR

Subject: Short wave infrared composite (SWIR)

IMAGES:

SUBJECT ANALYTICALLY:

Short wave infrared (SWIR) measurements can help scientists estimate how much water is present in plants and soil, as water absorbs SWIR wavelengths. Short wave infrared bands (a band is a region of the electromagnetic spectrum; a satellite sensor can image Earth in different bands) are also useful for distinguishing between cloud types (water clouds versus ice clouds), snow and ice, all of which appear white in visible light. In this composite vegetation appears in shades of green, soils and built-up areas are in various shades of brown, and water appears black. Newly burned land reflects strongly in SWIR bands, making them valuable for mapping fire damages. Each rock type reflects shortwave infrared light differently, making it possible to map out geology by comparing reflected SWIR light.

COMMENTS – OBSERVATION:

In the left image, December 2016, the lack of water in the burned areas is depicted in dark brown, while the overgrown areas are depicted in green. In contrast, in the right image, December 2024, all areas are now depicted in green.

 

INDEX: False Color Urban

Subject: False Color Urban composite

IMAGES :

SUBJECT ANALYTICALLY:

This composite is used to visualise urbanized areas more clearly. Vegetation is visible in shades of green, while urbanized areas are represented by white, grey, or purple. Soils, sand, and minerals are shown in a variety of colors. Snow and ice appear as dark blue, and water as black or blue. Flooded areas are very dark blue and almost black. The composite is useful for detecting wildfires and calderas of volcanoes, as they are displayed in shades of red and yellow.

COMMENTS – OBSERVATION:

In the left image, December 16, the areas with intense vegetation are depicted in shades of green. While areas with less vegetation are depicted in lighter green. More specifically, areas that have suffered fires are depicted in yellow.

In contrast, in the right image, December 2024, there is a uniform image on the island. More specifically, there are not such large deviations in dark-light green colors, but the island is depicted all in shades of intense green.

 

INDEX: Highlight Optimized Natural Color

IMAGES:

COMMENTS – OBSERVATION:

In the left image we can see areas depicted in dark brown, in December 2016, these are areas with abundant drought.   In contrast, in the right image, in December 2024 respectively, the areas that had suffered this devastating fire appear to be now overgrown.

 

GROUND DATA:

A dry storm occurs when there is too much drought. Thus, on the island of Thassos, after the great drought of the summer, a dry storm broke out, resulting in the fire on the island in 2016.

The island of Thassos, after the devastating fires of 2016, also suffered catastrophic floods because its mountains were stripped bare due to the fact that their trees burned and could not retain the water of the rainfall.

There were 2 catastrophic floods:

• November 2019

In Thassos, the biggest problems are found in the southern part of the island, where six areas were declared in a state of emergency.

More specifically, the heavy rainfall mainly affected the southern part of Thassos, with many roads and houses flooded. Roads turned into torrential torrents, sweeping away cars and anything else in their path, streams and irrigation canals overflowed, many parts of the road network are inaccessible, while the assistance of the Fire Department was needed to free residents in settlements where water literally entered their homes and made it impossible for them to move.

The situation has gotten out of control and in Potamia, the central stream had overflowed, resulting in water "running" uncontrollably in any direction.

• November 2024

Thassos recorded an impressive rainfall record. The Meteokav weather station in Limenas, Thassos recorded a daily rainfall of 153mm, surpassing the previous record of 152.4mm recorded in November 2019. The rainfall significantly affected the areas of Prinos and Kalivia Limenaria, causing flooding.

The bad weather severely affected the road network and infrastructure in Maries to Kalivia, Prinos, where the road connecting it to Skala Prinos, Kalivia Limenaria was flooded, where they were affected by the flooding phenomena. The main road flooded again, as had happened in 2019, causing serious problems in traffic and the movement of residents.