1. Sudden Hydro-Meteorological Disasters

      The increase in both number and severity of sudden-onset natural disasters because of climate change, particularly hydro-meteorological disasters such as flooding, hurricanes, typhoons, cyclones, and mudslides, can cause large-scale displacement. [FN185] As Margareta Wahlstr m points *736 out, “[o]ver the past 30 years, disasters-storms, floods and droughts-have increased threefold, according to the UN International Strategy for Disaster Reduction.” [FN186] In 2008, 20,293,413 people were displaced as a result of climate-related disasters. [FN187] Such disasters can cause immediate and sudden casualties and obviously large-scale displacement. [FN188]

      Displacement caused by sudden-onset disasters is easily identifiable because environmental disasters are easy to observe and, in some cases, reported by the media. [FN189] When such disasters occur, people often must flee from the affected area to avoid physical harm or loss of life. [FN190] During and in the aftermath of natural disasters, people often lose their livelihoods, harvests, crops, and livestock are destroyed, at a minimum interrupting their ability to subsist off the land. [FN191] These kinds of impacts can influence population movement. [FN192] When the disasters are over, people's ability to return to their homes is dependent on the measures adopted for recovery of “social, economic and physical characteristics of the affected area.” [FN193] In most cases, this type of displacement “need not be long-term and return in principle remains possible as [a] durable solution.” [FN194] Thus, mobility *737 decisions of people displaced by sudden hydro-meteorological disasters are based on disaster management by the concerned authority. [FN195]

2. Slow-Onset Environmental Degradation

      Long-term and gradual environmental degradation, such as drought, desertification, reduced water availability due to melting glaciers, land erosion, long-term effects of recurrent flooding, and increased salinity in coastal zones due to sea level rise all cause large-scale progressive displacement. [FN196] These gradual changes deteriorate herding, farming, and fishing, and may negatively affect livelihood systems that ultimately motivate people to move in the long term. [FN197] Communities in the affected areas may increasingly choose to move to safer places to avoid life-threatening environmental degradation likely to arise in the near future and avail themselves of higher-quality living standards. [FN198] Such migration is a challenging and complex issue. [FN199] The gradual environmental impacts that comprise a more systematic environmental degradation are rarely reported by media and concerned authority until the degradation transforms into severe crisis. [FN200] People may not return to their original homes due to loss of the physical existence of their land (because of sea level rise and coastal erosion) or livelihood (due to desertification, salinity, or extinction of fish and other species). [FN201] Provided the physical land is available, people may still choose to return to their original homes if they can adopt an alternative livelihood. [FN202] K lin explains:

       Such deterioration may not necessarily cause forced displacement in the strict sense of the word but, among other reasons, will incite people to move to regions with better income opportunities and living conditions. However, if the areas become uninhabitable because of complete desertification or sinking coastal zones, then population movements amount to forced displacement and become permanent. [FN203]

       *738 However, slow-onset environmental changes tend to affect a larger number of people than sudden acute disasters. [FN204] For example, during the period from 1979-2008, 718 million people were affected by storms compared to 1.6 billion people affected by droughts. [FN205]