International Education Centre of the Moraitis School
Number of team members:
What are the effects of wildfires, deforestation, and increased precipitation on the severity of flash floods?
Summary of the project:
Wildfires may contribute significantly to an increased occurrence of flash floods, often caused by heavy storms. We investigated this phenomenon in the west Attica area, near Athens, focusing on two cases: 1) The recent flash flood in Kineta on 25/11/19, in relation to the wildfire in Mt. Geraneia of the year before (on 23/7/18 – the same day as the dreadful fire of Mati) 2) The deadly flood in Mandra on 15/11/17, in relation to several wildfires in Mt. Pateras in previous years. We examined the changes in the microclimate before and after the wildfires and floods, anomalies in the local climate during the last 40 years as well as local weather conditions in the days of the storms. We relied on Copernicus satellite remote observation data provided by the ESA, the Climate Data Store-ERA 5 explorer and on local climate data provided by HNMS (Hellenic National Meteorological Service). Deforestation is a major environmental problem. The likelihood of floods grows with deforestation and the related soil erosion. Deforestation is often the result of wildfires. In the past few years, wildfires have severe consequences in biodiversity across the globe (Amazonia, Siberia, Alaska, Australia). In this investigation we researched the link between wildfires and subsequent flash floods in west Attica near Athens, Greece. One of the phenomena of climate change is more extreme weather, such as the occurrence of long periods of draught followed by heavy rainfall. Warmer air in the atmosphere can hold more water and this increases the potential for flash floods. These are often intensified by severe, local storms and lack of urban planning. Immediate impacts of flooding and wildfires include loss of human and animal life, damage to property, degradation of natural resources, destruction of crops, non-functioning of infrastructure facilities. These may have serious economic, social and psychological repercussions.
Our results refer to FIG 1-9, from which conclusions can be drawn. The wildfire of 23/7/18 in the Geraneia Mt. above Kineta burned 60,000 acres, 53,000 of which were forest areas. The destruction of the forest has played a key role in the flood episode a year later in Nov 2019, as the water that came with momentum from the mountains was not restrained by vegetation and swept away many burned trees. In FIG 1-2, we compare vegetation before and after the wildfire using the NDVI (Normalized Difference Vegetation Index) in https://apps.sentinel-hub.com/eo-browser. Similarly, in FIG 3-4, we compare the soil’s humidity using the moisture index. It is clear in these figures that before the wildfires vegetation was more intense and the soil was moister. We then examined anomalies in the local climate during the last 40 years using https://cds.climate.copernicus.eu/apps/c3s/app-era5-explorer. In FIG 5, the annual precipitation anomaly for years 1979-2019 is shown as a percent relative to the reference period of 1981-2010. In FIG 6, the annual temperature anomaly is shown in the form of warming stripes. Using these graphs, we calculated that in the last 20 years there was an average annual rainfall increase of +14% and a temperature increase of +0.5°C. Weather parameters in the days of the two floods were examined using data from the nearby weather station in Eleusis, kindly provided by HNMS (Hellenic National Meteorological Service). In FIG 7, the Kineta flood coincided with the maximum record of 31 mm of rain. As seen in FIG 8, however, there is little rainfall recorded during the Mandra flood. This indicates that the flood had a particularly local character. The extreme rapidity of the storm is displayed in FIG 9, where the rate of rainfall exceeds 100 mm/hour.
Actions to help lessen the problem:
Attica has suffered two major catastrophes in recent years. The wildfire of Mati in 2018 and the Mandra flash flood in 2017 claimed 129 lives, including children. The environmental damage that occurs from wildfires is often linked to a higher risk of floods. Large-scale wildfires dramatically alter the terrain and ground conditions. Normally, vegetation absorbs rainfall, reducing runoff, while wildfires leave the ground charred, barren, and unable to absorb water, creating conditions ripe for flash flooding and mudflow. Flood risk remains significantly higher until vegetation is restored, which takes years following a wildfire. It is urgent to take measures to prevent these events for the protection of our environment but also the immediate protection of our communities. Initially we need to protect the forests and accelerate reforestation. A prompt solution to minimise soil erosion would be to enrich the soil by adding nutritional substances. Ensuring adequate cross section for water streams is also important. The implementation of a digital early warning system for both wildfires and flash floods could save lives and is long overdue. Furthermore, it is of utmost importance to raise awareness of the need to protect our natural habitat. In Attica, both temperature and rainfall exhibit a significant increase in the last 20 years. It is crucial to reduce carbon emissions in industry and transportation by relying on renewable energy sources instead of fossil fuel. The effect of climate change on wildfire and flood risk is also enhanced by social factors (e.g. population growth in the wildland-urban interface), which tend to increase the scale and duration of the adverse ecological and economic consequences. Finally, the psychological effects of these events should not be underestimated. Displacement from one’s home, loss of property, livelihoods, and disruption of social affairs can cause continuing stress, which can be overwhelming and produce a lasting psychological impact.
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