A Hydrological Disaster is a violent, sudden and destructive change either in quality of earth's water or in distribution or movement of water on land below the surface or in atmosphere.

A flood is an overflow of water that submerges land. The EU Floods Directive defines a flood as a temporary covering by water of land which is usually not covered by water. Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows causing the result that some of the water escapes its usual boundaries.

$1.4$ million people were affected by flooding in Bihar on $27th$ August $2008$. Flooding occurred throughout the Kori river valley in northern Bihar, in the district of Supaul, Araria, Saharsa, Madhepura, Bhagalpur, Khagaria and Purnea.

Brahmaputra River.

Assam is the state prone to flood in India. Area prone to flood in Assam is 3.15 million hectares. Assam faces frequent flood problem because it lies on the basins of Brahmaputra and Barak rivers. 

Floods can have negative environmental consequences, such as soil erosion, release of pollutants and excess sediments into waterways and the ocean, dispersal of weed species, and negative impacts on fish and other aquatic life. Floods can also have positive environmental consequences, such as recharging groundwater systems, filling wetlands, moving useful nutrients around the landscape, and triggering breeding events (for example, of water birds).

Flood risk in new developments can be reduced by restricting the location of development (zonings) and placing controls (regulations) on development. In existing developed areas, risk can be reduced by modifying flood behaviour (for example, through dams, detention basins, levees, waterway modifications), property modification measures (for example, land filling, flood proofing, house raising, removing developments), and response modification measures (for example, upgrading flood evacuation routes, flood warnings, flood evacuation planning, flood education programs).

Flood warnings should provide information on what the threat is, what action should be taken, by whom and when. While it is desirable for flood warnings to be accurate, warnings are predictions about the future, so there is inevitably some uncertainty. Accuracy needs to be balanced with timeliness, to allow enough time for appropriate action. Warnings are most likely to reach different audiences and to be heeded if they come from multiple trusted sources.

In the future, climate change is likely to result in an increased chance of flash floods and coastal inundation. Australia’s growing population and urbanization are likely to place increased pressure on our waterways and to increase the chance of flooding in cities and the number of properties and people exposed to floodwaters.

The Probable Maximum Flood (PMF) is an estimate of the largest possible flood that could occur at a particular location, under the most severe meteorological and hydrological conditions as they are currently understood.

The Ganga Basin gets flooded mostly in the northern part by its northern tributaries. The badly affected states of the Ganga basin are West Bengal, Bihar and Uttar Pradesh.

Besides the Ganga, rivers like Sharada, Rapti, Gandak and Ghaghra cause flood in eastern part of Uttar Pradesh. The Yamuna is famous for flooding Haryana and Delhi. Bihar experiences massive dangerous floods every year. River Burhi, Bagmati, Gandak, Kamla along with many small rivers contribute to that. In West Bengal, rivers like Mahananda, Bhagirathi, Damodar, Ajay etc. causes floods because of tidal effects and insufficient river channels.

Bihar is India's most flood-prone state, with 76% population in the North Bihar living under the recurring threat of flood devastation. Bihar makes up 16.5% of India's flood-affected area and 22.1% of India's flood affected population

In the absence of adequate rainfall, most part of Bihar including North Bihar which is prone to floods face drought situations. South and southwest Bihar are more vulnerable and often experiences severe drought situations. Districts of Munger, Nawada, Rohtas, Bhojpur, Aurangabad, and Gaya are the known drought-prone areas of the state.

Drip irrigation is a form of irrigation that saves water and fertilizer by allowing water to drip slowly to the roots of many different plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters. It is done through narrow tubes that deliver water directly to the base of the plant. It is chosen instead of surface irrigation for various reasons, often including concern about minimizing evaporation.

Drip irrigation is used in farms, commercial greenhouses, and residential gardeners. Drip irrigation is adopted extensively in areas of acute water scarcity and especially for crops and trees such as coconuts, containerized landscape trees, grapes, bananas, pandey, eggplant, citrus, strawberries, sugarcane, cotton, maize, and potatoes.

Never try to walk or swim through flowing water. Don’t go for tour in sea during flooding. If flowing water is above your ankles, then stop and turn around and go another way. If it is moving swiftly, water 6 inches deep can knock you off your feet. Be aware that people have been swept away wading through flood waters.

Turn off utilities at the main switches or valves if instructed to do so. Disconnect electrical appliances. Do not touch electrical equipment if you are wet or standing in water. Avoid floodwaters; water may be contaminated by oil, gasoline, or raw sewage. Water may also be electrically charged from underground or downed power lines.

Harvesting rainwater at home and school generally help in using it up in times of scarcity.

Trees, especially drought-tolerant, native species, also provide critical services that directly attack some of the consequences of drought. Native trees send out deep, water-seeking roots into the soil to tap into local groundwater and draw it to the surface.

Conserving water makes us use the water the less so that water is not wasted and could put in use during droughts.