For forty days the flood kept coming on the earth, and as the waters increased they lifted the ark high above the earth.Genesis 7:17
At this time there was a deluge of water in the territories of Venefia and Liguria, and in other regions
of Italy such as is believed not to have existed since the time of Noah. Ruins were made of estates and
country seats, and at the same time a great destruction of men and animals.Paul the Deacon, Hist.Lang. XXIII
The word "deluge" has always evoked apocalyptic scenarios of destruction; it, in many cultures, is synonymous with the unleashing of the forces of nature, and the representation of a superior force that erases and transforms everything. In the evolution of the relationship between man and nature, if these phenomena have lost the original mysterious aura, they are charged in the time of new symbolic meanings: if by Paul the Deacon the Deluge marks the end of the ancient world and the beginning of a new era, the mystics of medieval storms, floods and periods of continued drought are one way that God has to communicate with the men and drive them to new or renewed forms of piety; even in modern times, despite the progress of science, sudden changes in climate have been interpreted as ominous portents, even, in some cases, so as to justify acts and violent behavior, such as, for example, the persecution of "witches" or minorities and other categories of people.
The "mystique of the climate" is not just a feature of more or less remote times. Words such as "global warming" and "climate change" have become popular and often appear as an explanation of catastrophic events, famine or unusual weather phenomena. A clear awareness of human responsibility in the current state of the global climate has the negative consequence that to have turned the "weather factor" in the first, if not the only, culprit of environmental crises in the world. If science is committed to the geo-technologies to mitigate the effects of climate change, the response of much of the world's population has not changed compared to the past: massive migrations are taking place from the areas most affected by the effects of global warming to the countries of the northern hemisphere.
It is evident that the purely technological solution or the migration itself are not sustainable, or they are not by themselves, on a planet traveling toward the 10 billion inhabitants. Also the only reduction of CO2 emissions in the atmosphere will not solve the problems that large areas of the world have now. Overcoming the "mystique of the climate" means first of all open your eyes to a complex of issues surrounding the complicated relationship between Humans and Nature. The climate is only one factor to be considered. Acting on climate is only partially possible; is essential, however, to actively intervene on the factors that make human societies vulnerable to climate change. 
The immediate observation, "in real time" of how a society reacts to a sudden change in environmental conditions provides only a partial snapshot of the culminating moment of a process. When a community is in the borderline situation, or no longer able to respond efficiently and effectively to stimuli of the environment, it means that it is in the final stage,and sometimes irreversible, of the complex process that led to the collapse. This has happened many times in human history and at different scales of magnitude. However, historical research has often stop at the surface, to the awareness that the climate was, in some way, have played a major role in the fall of a civilization. This reduction and simplification lose sight of the whole of the social, economic and political changes that represent the thickness of the problem of the relationship between Humans and the Environment.
The comparative study of historical events, far apart in time and space too, is a complex job and to be conducted with caution in order not to "actualize" specific phenomena of thepast, but even create anachronisms artificial and contrived; the choice of geographical areas must meet certain criteria in order not to attribute characters socio-cultural contexts to which they not belong. The geographical areas to this preliminary disquisition are the Po Valley and the central Adriatic area (Italy) and the Fertile Crescent, limited to the Syrian territory. For the Po Valley periods that will be considered are: 535-589 AD and 1764-1816 d.C .; the Fertile Crescent: 1595-1610 A.D. and 1946-2014 AD. Both geographical areas have been, since ancient times, exploited for agricultural irrigation systems through technical and complex; in both contexts the resource water is essential, as well as its management; consequently, finally, both environments were in their history, and still are, vulnerable to climate change.
The historical periods have been chosen according to the quantity of sources available, for common characteristics and because the dates of each pair are, roughly, the beginning and end of a chronological process.
Po Valley and central Adriatic area (Italy)
1.
535 A.D. : Event abrupt climate, crop failure resulting in migration of the population, the outbreak, in the previous year, of the Greek-Gothic war, tensions in society between the Roman and the Gothic elements.
589 A.D. : The "flood" of Paul Deacon as a result of the total collapse of the irrigation system of the Roman period, profound transformation of the settlement system in central and northern (who "wins" and who "loses", legacy and new features).
2.
1764 A.D. : Abrupt climate event as "flick of the tail" of the Little Ice Age, famine, epidemics and catastrophic events related to fluctuations in climate and land management.
1816 A.D. : Year after the eruption of the volcano Tambora, a serious impact on agricultural production and on the hydrogeological framework of the territory, the Napoleonic wars, migration from the countryside and towards the plain.
Fertile Crescent (Syria)
1.
1595 A.D. : Effects of the Little Ice Age on agricultural production and social tensions that lead to revolts against the tax system of the Ottoman Empire.
1610 A.D. : It is quelled the revolt of Celali, reducing the phenomenon of banditry that was spreading in the countryside.
2.
1946 A.D. : Independence of Syria, measures of land distribution, splitting of property, migration from the countryside, spreading the "squatting" in agricultural properties, developed new areas of culture, problems of water management also due to international tensions.
2014 A.D. : Civil war, easing of state control in the area, intensification of migration, both internal and international, land abandonment, impoverishment of agricultural production as early as 2006.