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How would you propose to identify the causal mechanism of a single catastrophic flooding event?

Flood is a phenomenon that causes human deaths and economic losses, so that flood phenomena can be considered one of the most complex and destructive natural events that more than any other natural disaster, life and property Humans and social and economic conditions of society endanger the community. The uneven distribution of rainfall in terms of time, intensity and amount in widespread parts of US, cause sudden floods with mortality and financial losses. In addition, severe degradation of natural resources whether exploited by uncontrolled utilization of forests and pastures, or changing land use and turning them into inappropriate agricultural lands or uncontrolled construction of residential areas has caused floods to occur year by year either in terms of number of occurrences or in terms of severity damage increases.

For identifying the causal mechanism(s) of a single catastrophic flooding event, first of all we should peruse that which kind of floods is our aim. As we know, we have different kinds of flood: coastal floods, river floods, flash floods, groundwater floods, ice-jam floods, glacial-lake floods, urban floods, and drain and sewer floods. The type of flood can help us to identify the causes of it better. For example, the causal mechanisms of coastal flooding are including cyclones, hurricanes and tsunamis, which mean that the extent of coastal flooding and its effects exceed those of floods further inland and present a greater risk to life.

Although the processes of individual flood events have been studied in great detail, identifying the causes of changes over time is much more difficult. For example, three main factors exist that potentially contribute to changes in river floods. These are related to climate, catchment processes, and the river network (Merz et al., 2012; Hall et al., 2014). However, for identifying the overall causes, there are different items. Even floods of the same type, e.g., river floods, may be produced by different combinations of causal mechanisms, e.g., different atmospheric situations, different catchment initial conditions, runoff, different snow-related mechanisms such as accumulation and/or melting during the event, and so on. Coastal floods may change due to changes in atmospheric phenomena, sea level rise and, maybe more importantly because of land subsidence due to groundwater pumping (Nicholls and Cazenave, 2010).

I have studied Hirschboeck (1987, 1988), and the researches performed a detailed analysis of causal mechanisms of floods in a number of catchments in Arizona and classified floods into three classes, including: tropical, convective, and frontal events.

In my opinion, many factors affect streamflow, and therefore the potential for flooding. Most important are the amount and type of precipitation, the nature and condition of the drainage basin (human activities), and climate (weather variables). So, I propose for identifying the causal mechanisms of a flood event, first of all we should determine the kind of flood, then by checking the weather/atmospheric variables, especially precipitation and atmospheric circulation patterns. Also, assess the trends of extreme precipitation against flood trends. Beside atmospheric variables, checking the changes in catchment processes include land-use changes (Wheater and Evans, 2009). Check hydraulic structures, and other sources of data such as synoptic maps in different pressure levels, and also assess hydroclimate equations can help us to identify the causal mechanism(s) of a single catastrophic flooding event.

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