Often a flood breaks the banks causing serious damage. The following are the catastrophic floods that have caused the greatest media coverage. Atmospheric phenomena with a seasonal cycle, such as monsoons and cyclones, called hurricanes in the Caribbean, cause smaller-scale floods every year, which frequently cause victims also due to the high population density in the affected regions.
To assess the risk of flooding, the concept of return time, or recurrence time, of the event is used, i.e. the average time, expressed in years, between the occurrence of two events of an intensity equal to or greater than one preset intensity.
The estimate of the return time, which depends on various factors (including geomorphological, climatological, hydrological and even anthropic ones), is carried out through the analysis of the historical series of alluvial events, preferably over time intervals of centuries, integrated with the evaluation geographic, geomorphological and hydrological area of the territory on which the river course and the reference hydrographic basin stand (including rainfall data, the layout of the riverbeds, the state and structure of the embankments, the presence of any expansion tanks or dams).
Flood exposure and poverty in 188 countries
The study Flood exposure and poverty in 188 countries, published on the Nature communications, told: "Flooding is among the most prevalent natural hazards, with particularly disastrous impacts in low-income countries.
This study presents global estimates of the number of people exposed to high flood risks in interaction with poverty. It finds that 1.81 billion people (23% of world population) are directly exposed to 1-in-100-year floods.
Of these, 1.24 billion are located in South and East Asia, where China (395 million) and India (390 million) account for over one-third of global exposure. Low- and middle-income countries are home to 89% of the world's flood-exposed people.
Of the 170 million facing high flood risk and extreme poverty (living on under $ 1.90 per day), 44% are in Sub-Saharan Africa. Over 780 million of those living on under $ 5.50 per day face high flood risk. Using state-of-the-art poverty and flood data, our findings highlight the scale and priority regions for flood mitigation measures to support resilient development."