Water-related hazards form a subset of natural hazards; the most significant ones include floods, mudslides, storms and related ocean storm surge, heat waves, cold spells, droughts and waterborne diseases.
Most disasters are caused by a combination of hazards, some related to water and other of geological and biological origin. Such events include those triggered by earthquakes, such as tsunamis, landslides that dam rivers, breakage of levees and dams, as well as glacier lake outbursts, coastal flooding associated with abnormal or rising sea levels, and epidemics and pest outbreaks associated with too little or too much water.
Water-related hazards account for 90% of all natural hazards, and their frequency and intensity is generally rising. Some 373 natural disasters killed over 296,800 people in 2010, affecting nearly 208 million others and costing nearly US$110 billion. According to the United Nations Global Assessment Report, since 1900 more than 11 million people have died as a consequence of drought and more than 2 billion have been affected by drought, more than any other physical hazard.
Due to climate change, it is expected that the frequency of certain natural hazards will increase. Water-related disasters pose both direct impacts (e.g. damage to buildings, crops and infrastructure, and loss of life and property) and indirect impacts (e.g. losses in productivity and livelihoods, increased investment risk, indebtedness and human health impacts). The increasing economic cost and toll of disasters should be a significant incentive for governments and humanitarian organizations to focus more attention on preparedness, prevention and addressing the root causes of vulnerability.
Source: World Water Development Report 2012