Disscusion on recent floods
Answers
Meteorological Factors: Heavy rainfall, cyclonic storms, and thunderstorms. Hydrological Factors: Overbank flow channel networks, the occurrence of high tides impeding the drainage in coastal cities. Anthropogenic Factors: Unplanned Urbanization: Unplanned Urbanization is the key cause of urban flooding.
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Answer:
Floods in the Indian subcontinent have affected habitat,
population, economy, etc. Due to the detrimental
effects of recent floods on the economy, governance,
etc., it is imperative to understand the associated
dynamics, manifestations and fallouts for proper policy
planning recommendations. The present study endea-
vours to provide an integrated rationale of meteoro-
logical and geomorphological aspects associated with
four recent extreme floods in Uttarakhand (2013),
Srinagar (2014), Chennai (2015) and Gujarat (2017).
It is important to mention here that these floods
occurred under different atmospheric circulations and
geomorphological setting, and had an entirely different
gambit for policy planning and governance. Consoli-
dation of these issues will help policy planners and
technologists, in case advance warning system based
on these findings can be developed.
Keywords: Advance warning system, disaster mana-
gement, floods, governance, policy planning.
RAINFALL extremes cause flooding1
. Increased surface
run-off, and precipitation higher than the capacity of
outgoing discharge cause the water level to rise, leading
to submergence of regions, debris flows/landslides,
water-borne health disasters, etc.2
and posing threats to
sustainable development3
. Floods impact the ecosystem
and society by destroying habitats, affecting lives,
damaging infrastructure, etc. Nearly 40 m ha area in India
is flood-prone and every year nearly 8 m ha of land is
affected by floods. Apart from these, floods during rabi
and kharif seasons affect food security of the nation. Due
to warming climate, increased frequency of rainfall
extremes is reported in India4
. In addition, in recent dec-
ades, warming trend over the Indian Ocean5
has potentially
enhanced moisture supply leading to rainfall extremes in
the country6
. Abrupt variability and increased uncertain-
ties of rainfall patterns, periods, days, amount and risk of
weather extremes – as an impact of global climate
change – aggravated by ecological and anthropogenic
factors, pose ever-increasing risk of flood disaster7
.
However, increased atmospheric water vapour, though
favourable for intense rainfall events, by itself is not suf-
ficient to produce rainfall. Favourable thermodynamic/
dynamic conditions and rising motion in the atmosphere
are necessary for rainfall8
.
Geomorphological settings along with rainfall
extremes have led to flooding. In-flow and out-flow
limits of sewerage also contribute to flooding. Inundation
of a geomorphic substrate by flooding follows a definite
pattern. Any infringement to the natural flow path of a
river has a disastrous effect on the habitants.
In this article, we briefly discuss the unique geomor-
phic set-up of three major recent flood-affected regions of
India: (i) June 2013 Uttarakhand flood in Upper Ganga
valley, (ii) September 2014 Kashmir flood in Jhelum
river and (iii) December 2015 Chennai flood. Geomor-
phic limitations of the terrain in different geological
settings causing similar disaster in response to analogous
weather phenomenon are highlighted. In addition, Gujarat
(2017) flood is discussed in brief, which occurred only
with atmospheric forcings. Mechanisms and forcings
behind the occurrence of these floods are analysed. This
combined analysis may help the policy planners to sug-
gest proper recommendations.
Floods in association with Indian summer
monsoon
The onset of the Indian Summer Monsoon (ISM) and its
advance bring rain over different parts of India. ISM has
inter-annual and intra-seasonal phases as onset and
advance (mid-May to mid-July), peak rainfall (July to
August) and withdrawal (mid-September to mid-October).
In addition, latent heat source shifts over northern India
due to shifting of Intertropical Convergence Zone (ITCZ),
which generally stays between 20° and 30°N during the
peak monsoon (July–August). The onset and advance
phase is often accompanied by one or more transient
disturbances. Their movements not only advance the
monsoon isochrones to different parts of India, but are
accompanied by heavy rainfall in the vicinity of monsoon
transients during this phase. Heavy to very heavy
monsoon rainfall is normally associated with vigorous
monsoon conditions, low pressure systems and monsoon
breaks9
. In the region of the Himalaya, occasionally low