Floods

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Floods and droughts over India are the two aspects of weather associated with the abundance or deficit of monsoon rains. A large number of studies are available on various aspects of floods and droughts (Table 6.5).

Effects offlood on agriculture

Very intense (extreme) rainfall can result in catastrophic flood damage even though it occurs for a relatively short period of time (Table 6.6). In general, the greatest damage to agriculture results from high intensity rainstorms with sufficient duration as opposed to the low intensity, long duration storms. Direct damage to growing plants from floods is most often caused by depletion of oxygen available to the plant root zones. Flooding creates anaerobic soil conditions that can have significant impacts on vegetation. Root and shoot asphyxia, if prolonged, typically leads to plant death. Chemical reactions in anaerobic soils lead to a reduction in nitrate and the formation of nitrogen gas. tte denitrification can be a significant cause of loss of plant vigour and growth following flooding.

Mitigation ofdamage on agriculturalsectordue to flood andheavy rainfall

Soils that are saturated prior to an extreme weather event are more likely to be affected severely by a damaging flood than soils that are relatively dry. Fields that have recently been tilled and are devoid of vegetation are much more susceptible to water erosion. Vegetation that is able to use much of the water and that can act as a barrier to moving water (horizontally and vertically) can reduce flood severity and impacts. Water storage systems (rivers, lakes, reservoirs, etc.) that are able to capture and hold most of the incoming water are usually effective in reducing flood damage.

Flooding and heavy rainfall

Soil erosion, disruption to critical agricultural activities, the logging of crops, increased moisture leading to increased problems with diseases and insects, soil moisture saturation and runoff, soil temperature reduction, grain and fruit spoil-

Table 6.5 Flood years and their category

Year

Area affected (xlO6 km2)

% of the area affected

MFI value

Category

1961

1, 795

57, 166

3,614

Exceptional

1971

1, 427

45, 446

2,668

Exceptional

1878

1, 513

48, 185

2, 889

Exceptional

1975

1, 268

40, 382

2,260

Exceptional

1884

1, 175

37, 420

2,021

Exceptional

1892

1, 162

37, 006

1,987

Exceptional

1933

1, 145

36, 465

1,943

Exceptional

1959

1, 135

36, 146

1,918

Exceptional

1983

1, 030

32, 803

1,648

Exceptional

1916

1, 025

32, 604

1,635

Exceptional

age and transportation interruption are among the more significant agricultural impacts from heavy rainfall (Table 6.7). Direct damage to growing plants from flood is most often caused by depletion of oxygen available to the plant root zones. Flooding creates anaerobic soil conditions that can have significant impact on vegetation. Chemical reactions in anaerobic soils lead to a reduction in nitrate and the formation of nitrogen gas. tte denitrification can be a significant cause of loss of plant vigour and growth following flooding, ttere is often a balance needed between retaining enough water for agricultural production and environmental health and maintaining enough available storage volume to capture incoming water and prevent floods. Crops like rice that can function effectively in saturated and even submerged conditions are appropriate for locations that flood regularly and the system becomes dependent upon regular flooding. Many other crops (e.g. corn) would not be adaptable to such conditions and would not be appropriate alternatives to rice.

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Disaster Survival Guides Collection

Disaster Survival Guides Collection

This is a set of 3 guides all about surviving disasters. Within this set you will learn the following subjects: Earthquakes, Evacuations, Survivor Family and Tsunami.

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