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Does Climate Change can contribute to changes in flooding intensity and frequency?

IPCC has stated in several reports that the increased frequency of occurrence of flood events in the world is partially attributed to climate change-driven increase of extreme precipitation (IPCC, 2002, 2007, 2014). Due to global warming, the global water cycle is likely to be accelerated, resulting in many regions with increased flood magnitude, as well as flood frequency. Climate change is expected to worsen the frequency, intensity, and impacts of some kinds of extreme weather events. For example, sea level rise increases the impacts of coastal storms and increase in temperature’s value can place more stress on water supplies during droughts.

Changes in the hydrologic cycle due to increase in greenhouse gases under climate change conditions are projected to cause variations in intensity, duration, and frequency of precipitation events, consequently, heavy rainfall would happen, then a runoff will happen, and in sum flood event would proceed in intensity and frequency. Also, the impact of climate change on flood frequency is often defined by the percentage change in a flood peak of a given return period. Rising temperature’s amount due to global warming and climate change, raises sea level and snow melting occurs, therefore the chance of flash flooding will increase. In several regions in the world, climate change would increase short-term heavy rainfall which causes flood intensity and duration.

A report from NOAA (National Oceanic and Atmospheric Administration) revealed that melting snow can bring rising waters which highlighted the approaching flood risks and increasing the intensity of flooding (NOAA, March 2015). Increasing flood risk is now identified as the most important sectoral threat from climate change in most parts of the world (Spence et al., 2011). Researches have shown the effects of greenhouse gases on climate change and, therefore, the hydrologic cycle. Characteristics of precipitation data are expected to change throughout the 21st century, with the effects varying spatially (Trenberth et al., 2007).

So more floods that result from heavier precipitation amounts, would be occur, as well more flooding is expected from storms and rising sea levels. However, the effect of climate change on flooding intensity and frequency are not equal in all points in the world, for example Lehner et al. (2006) revealed that due to climate change's effects, in largely concurring trends, the regions most prone to a rise in flood frequencies are northern to northeastern Europe (Sweden, Finland and northern Russia), while southern and southeastern Europe show significant increases in drought frequencies (Portugal, Spain, western France, Italy and most of southeastern Europe). Reynard et al. (2004) emphasized that by climate models under a given emissions scenario, hydrological model and etc., some catchments can show an increase in flood frequency to the 2050s but a decrease by the 2080s, or vice-versa. This is likely to be due to the balance between increased winter rainfall and decreased summer rainfall in the climate scenarios considered in that study, with higher temperatures and so increased evaporation, meaning higher soil moisture deficits which have to be refilled before flooding can occur. In my point of view, and according to the done researches that I have studied them, to examine possible implications of the results for changes in extreme rainfall events and flooding under climate change conditions, we should use return period analysis, for quantifying the amount of flooding intensity and frequency under climate change conditions.

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