Meteorological risk management in a changing climate – Part I

I am here reporting the translation of a post written by Carlo Cacciamani and Alessandra de Savino for climalteranti.it, the Italian most important popular blog on climate and climate change (the original post in Italian language is written here). Despite the discussion originates from a flash flood occurred at Catania, in Sicily, few weeks ago, and considers meteorological events occurred only in Italy, I think that the general discussion about the risk communication stimulated in this post is rather general and exportable to almost every country.

Downpour at Catania

Downpour at Catania

Catania, February 21, 2013: severe storms cause flooding that inundate streets dragging motorcycles and cars. Due to the excessive rain, the city was submerged with a depth of water ranging between few centimeters and two meters. Bitter controversy aroused concerning alert warnings not issued, or badly issued (see here).

Cinque Terre, October 25, 2011, and Genoa, November 4, 2011: a terrible sequence of storms caused deaths and destruction (here a complete analysis of the event). Complaints to the Mayor of Genoa, again controversy (see here).

These stories repeated in the time, with apparently increasing frequency. It is not just the fault of a Nature (see here) which is becoming harsher, even if 500 mm of rain fell in a few hours (flood of Genoa) are not exactly events categorized as normal. Urban sprawl and soil (ab)use are some of the factors that cause these tragedies and damages. The rapidly changing climate could worsen the situation.

In recent years, Italy has been increasingly hit by high intensity storms, which resulted in severe damage and many deaths. As a consequence, finally, the problem of flooding, and especially of flash floods, is considered.

The predictability time of these phenomena is limited. In reality, their exact spatial and temporal location can be predicted only a few hours before, in the most lucky conditions, especially if the scale of phenomena is small (100 km2, for example, or even less). If these systems hit a very small catchment area (such as a few tens of km2), that can flood in a few minutes, it is evident as it is very hard to activate the civil protection “machine” in time in order to mitigate the damage to people and their property. Because all should be done in few minutes. But a few hours are needed to enable technicians, volunteers, civil protection, etc. .. And a few hours can be too much, in certain situations.

A few weeks ago, this argument was discussed in Bologna during a meeting organized by the Hydro-Meteo-Climate Service of ARPA Emilia Romagna (here the daily report). In this occasion, the opinions of different operators working at the Functional Centres (the technical structures operating, at national and regional level, in support of Civil Protection, established by the Directive of the Prime Minister of 27 February 2004) were compared between each other.  In particular, one of the discussions concerned the means available today to predict these severe local-scale meteorological phenomena, as well as the actual alert procedures, their pros and cons, and how to communicate in the optimum way the risks to the public.

The impact of these events is enormous: more than 10 critical events only from 2009 to now, starting with the downpour of Giampilieri, during which 36 persons hit by a mudslide died, until the last storms of 2012 that devastated Tuscany, Liguria without forgetting the two episodes of 2011 in Liguria above mentioned. These events left an indelible mark on the collective imagination, and originated a myriad of controversies. As usual, the responsibility was given to the uncontrolled urban development, and also to the warning systems, sometimes badly or untimely used. Additional controversies concerned the incorrect or sometimes unclear information given to the public, or a lack of uniformity in early warning systems… and so on and so forth… Googling the words “controversy – floods” (polemiche – alluvioni in Italian), everybody can spend hours to read all material that has been written, sometimes bad, on the matter.

We cannot forget the damages, lots of damages: hundreds of millions of euro for each event. But above all a bad death toll: over 70 deaths only from 2009 to present.

In most cases, these events were triggered by downpours originating from organized convective systems, known in the scientific literature as “V-shape” systems, for the V-shape form visible from satellite imagery, see figure (there is an extensive literature on this type of supercell thunderstorms: for example, it is possible to see here for more information). Given the high and increasing frequency of convective events, which often occur in the fall and even winter, the scientists are wondering whether there could be an effect of climate change.

The V-shaped storm at Catania

The V-shaped storm at Catania

The issue is studied by several time and at different levels. A warmer planet is potentially more wet, since the water vapor that can stand in a warm atmosphere, before it reaches saturation, is much greater than that in a cold one (the saturated vapor pressure increases exponentially with the increasing temperature, as it is well known from thermodynamics). Moreover, the atmosphere may become even more unstable when heating and humidity are greater in the lower layers than in the higher layers (this occurs almost always).

Concerning the extreme or intense events, the last IPCC report (AR4) states: “…  precipitation tends to be concentrated into more intense events, with longer periods of little precipitation in between.” And again: “… in concert with the results for increased extremes of intense precipitation, even if the wind strength of storms in a future climate did not change, there would be an increase in extreme rainfall intensity,… suggesting an increased chance of flooding over Europe and other mid-latitude regions due to more intense rainfall and snowfall events producing more runoff.”. In synthesis, a pure thermodynamic argument, i.e. the mere fact of having a warmer planet, suggests that the frequency and intensity of rainfall, and then floods, may increase.

Looking at Italy, the opinion of many colleagues working in research institutions, universities and meteorological services is that episodes of heavy rainfall, frequently caused by storm lines more or less organized in supercells or multicells, have increased in recent years. In a focus of ISAC-CNR published few years ago, in which the results of various analyses carried out on some Italian long meteorological series were summarized, it is concluded: “The analysis of these series revealed a decrease of rainfall in southern Italy and non-significant changes in the northern part; the most interesting result is a not negligible and highly significant decrease in the total number of precipitation events in Italy (in average by 12% since 1880 to now). However, this trend is not uniform over the entire distribution, but presents opposite behaviors considering the events of low and high intensity (belonging to the most extreme tails of the distribution): the former decreases and the latter increases.“. In conclusion, it rains less, but when it rains, it rains more!

Hence the growing concern… If the climate will change as predicted and accepted by everyone, or if this change will be just “very likely”, the hazards caused by these intense phenomena can only grow. Given the high natural vulnerability of many Italian areas, to which an increased “exposure” to risk caused by an excessive anthropic pressure, as well as the use often foolish of the soil must be added, we would expect a higher number of risk conditions due to floods and landslides than now? The answer to the question is unequivocal: Yes.

Then a second question immediately arises: the society is preparing to address these growing conditions of risk, caused by extreme meteorological events, sometimes assimilable to meteorological monsters (500 mm of precipitation in 3 hours is a quantity of rain hardly conceivable at our latitudes)?

Damages caused by the storm at Catania.

Damages caused by the storm at Catania.

The question splits into many others: first of all, the knowledge of these phenomena is already adequate or a lot of research is still needed? Are monitoring tools installed, and are they suitable? Are their operations guaranteed over the time? Are the prediction tools suitable? Are the warning systems able to quickly respond to very intense and very fast events? Moreover, is the social system as a whole aware of the (major) problems resulting from the impacts of changing climate? Are the mechanisms of risk communication adequate? Have the media a sufficient knowledge of how to deal with these issues? Are they gearing up to do that? Can the new media (social networks, smartphones apps, the massive use of the Internet) be helpful, and how? Finally: is there an “optimal” dose of information to communicate to the public, or it is necessary always to communicate everything to everyone, without any filter?

These questions are complex and span a wide range of problems. The answers are neither obvious nor simple, because the awareness of these issues is still low, despite the progress made in the last ten to fifteen years. The problems are thrown into the discussion, when there is a discussion, as mere slogans, and almost never the various stakeholders and risk managers discuss together these issues, in order to eviscerate the real difficulties and hypothesize some solutions. On the contrary, it is noted too often, especially shortly after the occurrence of such events, an automatic (and often, it must be reluctantly underlined, “ignoble”) discharge of responsibilities in order to assign the guilty of disasters to somebody else, instead of performing a rational examination of the facts. Then, usually, after some weeks or months, everything falls in the general oblivion.

But then: what should be done?

(To be continued in the second part)

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