The Chennai 2015 Floods

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The National Disaster Response Force (NDRF), Army and Indian Air Force (IAF) personnel were deployed to carry out rescue and relief operations in rain-hit Chennai.

Abstract: The Chennai floods in November-December 2015 are a wake-up call for us all. It is high time we stopped all unregulated unauthorised illegal encroachments and constructions over natural watercourses, creeks, estuaries, ponds, lakes and marshlands in our greed to over-exploit our natural resources under the ruse of development.

The author is Associate Professor, Head of the Knowledge Management and Communication Division and Leader, World Centre of Excellence on Landslide Risk Reduction (ICL and IPL-ISDR).

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The Baroclinic areas in atmosphere are generally found in the mid-latitude/polar regions whereas the Barotropic zones of the Earth are generally found in the central latitudes, or tropics.

Is the largest element of the intra-seasonal variability in the tropical atmosphere. In 1971 Roland Madden and Paul Julian stumbled upon a 40-50 day oscillation when analysing zonal wind anomalies in the tropical Pacific. The MJO, also referred to as the 30-60 day or 40-50 day oscillation, turns out to be the main intra-annual fluctuation that explains weather variations in the tropics.

An overflow of a large amount of water beyond its natural limits, especially over a normally dry land.

Hydrological drought is associated with the effects of periods of precipitation (including snowfall) shortfalls on surface or subsurface water supply (i.e., stream flow, reservoir and lake levels, groundwater). The frequency and severity of hydrological drought is often defined on a watershed or river basin scale. Although all droughts originate with a deficiency of precipitation, hydrologists are more concerned with how this deficiency plays out through the hydrologic system.

The Standardized Precipitation Index (SPI) is a tool which was developed primarily for defining and monitoring drought. It allows an analyst to determine the rarity of a drought at a given time scale (temporal resolution) of interest for any rainfall station with historic data. It can also be used to determine periods of anomalously wet events. The SPI is not a drought prediction tool.

The Dipole Mode Index is an indicator of the east-west temperature gradient across the tropical Indian Ocean, linked to the Indian Ocean Dipole or Zonal Mode.

The Indian Ocean Dipole, also known as the Indian Niño, is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean.

El Niño Southern Oscillation (ENSO) is an irregularly periodical climate change caused by variations in sea surface temperatures over the tropical eastern Pacific Ocean, affecting much of the tropics and sub-tropics. The warming phase is known as El Niño and the cooling phase as La Niña.

Western Disturbance occurs in India, Pakistan, Karnataka and Nepal to describe an extra-tropical storm originating in the Mediterranean, that brings sudden winter rain and to the north-western parts of the Indian subcontinent. This is a non-monsoonal precipitation pattern driven by the Westerlies.

The Hadley cell, named after George Hadley, is a tropical atmospheric circulation which features rising motion near the equator, poleward flow 10-15 kilometres above the surface, descending motion in the sub-tropics, and equatorward flow near the surface.