Should we prepare for an increase in extreme weather events?

On 29 October, a DANA (Isolated Depression at High Levels) dumped an enormous amount of rainfall on the Spanish Levante and caused massive flooding, resulting in the deaths of hundreds of people, the paralysis of society and a huge amount of physical and material damage. It was undoubtedly one of the biggest meteorological disasters in Spain on record. Getting the affected localities back on their feet and restoring their former life will require an exceptional emergency budget and an exceptional amount of work – not to mention the damage to human lives and the very fabric of society.

Precipitation Context in the Spanish Levante region

Was this event so exceptional? On that day, the Turís rain gauge of the State Meteorological Agency (AEMET) recorded 771.8 litres of rainfall per square metre, one of the highest values ever recorded in Spain, and on the same day the same rain gauge reached the national record for rainfall in one hour, 184.6 litres per square metre. The Utiel observatory measured as much rainfall that day (230 litres) as falls in the whole municipality over the course of a whole year. Initial calculations suggest that the return period of a meteorological phenomenon such as this is hundreds of years. Return period is the time that must pass for a certain phenomenon to appear or manifest itself, and is related to the probability of it occurring. A return period of 100 years indicates that a certain phenomenon tends to occur at least once every 100 years.

The Spanish Levante is an area where daily heavy rainfall is not an uncommon phenomenon and society itself is used to the occurrence of heavy rainfall and subsequent flooding from time to time – although certainly not on the scale of 29 October. It should not be forgotten that the heavy rainfall in Valencia in 1957 caused the River Turia to overflow its banks (and the death of 81 people), which led to its course being changed in the interior of the city to avoid future episodes like this one as far as possible. Or the bursting of the Tous dam in 1982, which caused the death of 30 people.

Climate Change: Increased Frequency of Extreme Weather Events

However, under the current context of climate change, what used to be isolated phenomena that rarely occurred are beginning to occur more frequently. All kinds of extreme weather phenomena (heat waves, floods, droughts, forest fires, etc.) are occurring more frequently and with greater intensity across the planet. According to the 2021 IPCC (Intergovernmental Panel on Climate Change) report, the increase in greenhouse gases caused by human action has increased the frequency and intensity of extreme weather events.

The figures included in this article show precise climate change results from the multi-model simulation of the European CORDEX project, and have been obtained thanks to the AdapteCCa initiative of the Biodiversity Foundation (part of the Ministry for Ecological Transition and the Demographic Challenge). They show the increases in maximum 24h precipitation for two possible future scenarios of greenhouse gas emissions (RCP8.5, high emissions and RCP4.5, medium emissions) for the period 2041-2070 against the 1971-2000 period.

Figure 1 focuses on the area of the Valencian Community. Note how in both scenarios the multi-model simulation shows a clear and evident increase in the maximum 24 h precipitation amounts.

Figure 2 focuses on the area of the municipality of Barcelona. Note how in both scenarios the multi-model simulation shows a clear increase in the maximum 24 h precipitation amounts, especially in the RCP8.5 scenario (higher emissions).

Figure 3 focuses on the area of the municipality of Málaga. Note how in both scenarios the multi-model simulation shows a clear increase in the maximum 24 h precipitation amounts.

As can be seen, in all the areas shown, the maximum 24-h precipitation shows a clear positive increase under both scenarios, an increase that is greater in the Levantine Mediterranean area. This is why we can conclude that, approximately in the middle of the century, the climate in all these areas will be characterised by increases in maximum precipitation in 24 h with respect to that of the end of the 20th century, something that must be taken into account if the risk of precipitation for that time period is to be taken into consideration.

Methodology for Climate and Physical Hazards Estimation

Deyde Datacentric by Accumin has developed a methodology for estimating climatic and/or physical risks based on the European Union’s Taxonomy of climatic hazards, using data supplied by prestigious international organisations as input data. These data come from simulations coordinated by the IPCC itself, through studies under the auspices of the European Union, to official reports from the State Public Administration (from ministries to autonomous communities), which provides great confidence in its reliability and accuracy. Using all this information, we have categorised these possible risks on a scale of 1 to 5 (from very low to very high), which allows us to quickly assess the possible risks to which we may be exposed.

However, and in line with the above, knowing the risks existing today is not enough in a context of climate change in which what is reflected in historical records is already insufficient if we want to estimate what may happen in the future. That is why all our risks have also been developed for short (2011-2040) and medium-term (2041-2070) scenarios, thus allowing us to estimate the possible risks more rigorously: not only what they may be like today, but also what they may be like in the future.

Francisco Javier Pórtoles

Senior Data Scientist at Deyde DataCentric