Precipitation, banks and soil:this is why there is a direct relationship between drought and floods

When heavy rainfall arrives after long periods of drought, water infiltration problems are created due to the rigidity of the soil

Some might wonder why, after they told us about thedrought emergency in Italy, showing ourselves continuously images of dry rivers, now we are also talking about flood in Emilia Romagna between 2 and 3 May, especially in the provinces of Bologna and Ravenna.There are those who speak of a system constantly searching for false emergencies, winking at the denialism of climate change, which notoriously involves various environmental upheavals.

Reality often proves to be more complicated than we might perceive it while sitting comfortably in front of a PC screen.In fact, it is known that prolonged periods of drought prepare the ground (literally) for dangerous floods and overflows.The recent flood is no exception, «triggered by almost two years of drought and very heavy rains concentrated in a short time – explains Ansa -, the flood that hit Emilia Romagna is unlikely, according to experts, to be able to translate into a reserve of water capable of compensating for the damage caused so far by the lack of rainfall".

According to Luca Brocca, of the Research Institute for hydrogeological protection of National Research Council, we are talking about «over 200 millimeters of rain in the space of a day and a half.With these quantities - continues the expert -, problems are to be expected everywhere, except in Liguria, Veneto and Friuli Venezia Giulia, where the rains are more frequent and the soil is used to receiving them".

When heavy rainfall arrives after long periods of drought, such as that recorded in Northern Italy, water infiltration problems are created due to the rigidity of the soil.Thus, even if a good quantity of water infiltrates the ground up to the aquifers, in the limited areas affected by the flooding the water from the streams rose by 7-8 meters in the space of just 12 hours.Drought is a common problem in the Po Valley, fueled in part by the failure of embankments, which should be managed carefully, as well as land consumption and urban structures near risk areas.All this leads to an important contribution to floods in the event of heavy rainfall.As can also be seen by reading the reports of Euro-Mediterranean Center on Climate Change (CMCC), published in 2020:

A experiment conducted by Dr Rob Thompson of the University of Reading using simple plastic cups, helps us better understand the time it takes for water to penetrate arid soil, and how this can lead to sudden and dangerous floods.It is clearly seen that the glass placed on soil tormented by drought has a considerable difficulty in emptying, compared to other places in different situations:

According to the March bulletin of theDrought observatory of National Research Council (Cnr), we continue to be together with the other countries of south-western and eastern Europe, the most affected by the drought:

The same bulletin considered the month of May as the last month indicated to have "quantitatively "useful" rainfall".The meteorologist Pierluigi Randi based on the portal Ispra idroGEO, shows how Emilia Romagna is an area with «high hydraulic danger.[…] Consequently we have a very high percentage of the population exposed (red zones in the national map, again ISPRA).«Careful management of the territory is therefore a must – continues the expert -, and when it rains “rudely” always keep the antennas upright».

Cover photo:ANSA | River rescuers in Bagnacavallo (Ravenna), 4 May 2023.The work to plug the Lamone leak continued throughout the night.