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Seasonal floods and droughts


Seasonal or riverine floods are less contingent on glacial melt than the different types of flash floods. Impacts on humans and livelihoods from glacial melting in high regions will in most cases be much more localised and of a smaller overall magnitude than seasonal flooding in the lowlands. From a glacial and hydrological perspective it is unlikely that glacial melting will have significant impacts on the large-scale sea- sonal flooding in the lowlands of the large river basins in the HKH region.


However, human adaptation to different types of water stress and water hazards is a continuum of strategies and actions. All types of floods have potential impacts on people and liveli- hoods, but adaptive responses vary greatly given the differ- ent nature and magnitude of flash floods and seasonal floods. China, India and Venezuela are the most vulnerable coun- tries in the world to flooding in terms of the average number of people exposed and killed. Predicted increases in future cli- mate variability in the Himalayan region implies that floods of different types and droughts will remain a challenge to a significant portion of the world’s population.


Seasonal flooding can occur along all the major watersheds in the Himalayan region (Figure 11–14). The largest problems occur in flood prone areas with high population densities. This includes parts of northeast India, south-central Nepal, central and southern Pakistan, large parts of Bangladesh and lower reaches of the large rivers in China. In India around 40 million people are affected by flooding annually and the damage has been estimated to USD 240 million as an annual average. Here 40 million hectares of land are at risk every year. An average of 1800 people are killed by floods each year in India, which is roughly one quarter of the total number of people killed in natural disasters.


 Figure 12: Persons killed and affected by floods in Paki- stan in August 2010. An estimated 20.5 million people were affected, over 1700 were killed, 6 million were displaced and 1.89 million houses were destroyed. By November 2010, over 7 million were still affected and lacked proper housing (OCHA, Nov. 15th, 2010)


In China, 8% of the middle and lower reaches of the seven large rivers are prone to floods. Approximately 130 million are exposed to flooding on average every year and around 2000 people die in floods every year. The flood prone parts of Chi- na house one-half of the country’s population who produces 70% of the industrial and agricultural value of the country. More than 8 million hectares are flooded annually, and more than 100 medium to large cities have been affected by flood- ing during the past 30 years. The resultant economic losses comprise almost 25% of the annual world economic loss caused by floods (Zhang et al. 2003).


In Bangladesh, 86 million people were affected by natural disasters, predominantly floods, between 1998 and 2008 (World Disasters Report 2009). As much as 80 million may be prone to flooding one way or another (FAO 2001). An aver- age of 500–1000 die in floods annually. Around 13 000 per- sons were killed in natural disasters in Bangladesh this ten year period (World Disasters Report 2009). The 1998 flood was the most severe in the 20th century and an estimated 30– 32 million people were affected (Hofer and Messerli, 2006). Major riverine floods appear on average every 3–4 years . Most of the northern parts of the country are affected by flash floods at longer cycles, approximately every 20 years.


In Pakistan, an average of 10–15 million people are exposed to flooding and 250–300 people die in floods every year (Fig. 13 and 14). In August 2010, two weeks of intense mon- soon rains caused major rivers to flood villages, washed away


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