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GENERAL ARTICLES
CURRENT SCIENCE, VOL. 120, NO. 12, 25 JUNE 2021
1840
Vinay Ashok Rangari is in the Department of Civil Engineering, Sree
Vidyanikethan Engineering College, Tirupati 517 102, India; C. M.
Bhatt is in the Disaster Management Division, Indian Institute o
f
Remote Sensing, Dehradun 248 001, India; N. V. Umamahesh is in the
Department of Civil Engineering, National Institute of Technology,
Warangal 506 004, India.
*For correspondence. (e-mail: vinayrangari@gmail.com)
Rapid assessment of the October 2020
Hyderabad urban flood and risk analysis
using geospatial data
Vinay Ashok Rangari*, C. M. Bhatt and N. V. Umamahesh
The present study looks into the Hyderabad urban floods of October 2020 from a geospatial pers-
pective. The spatial extent and severity of the flooding event for a part of the urban catchment
(Zone-12) of Hyderabad city are modelled using HEC-RAS 1D–2D considering 13 October 2020
rainfall event. The study compares the present flooding to the previous flooding incidence which
impacted Hyderabad, almost a decade back on 24 August 2000. The study shows that rapid
unplanned urbanization ignoring the regional and local hydrological landscape has aggravated the
flooding severity. The study highlights the fact that rapid, uncontrolled urbanization (16.5%
increase) over the last two decades have substantially influenced the urban hydrology producing
higher flood volumes for comparatively small rainfall event. Thus regulating urbanization, provid-
ing enhanced drain capacity, rejuvenating the water bodies and streams is need of an hour to check
and reduce the spatial flooding extent.
Keywords: Geospatial extent, HEC-RAS, mapping, modelling, urban floods.
NATURAL hazards and extreme climatic events are be-
coming more frequent as a result of climate change1–3.
The problem is further aggravated due to migration of the
rural population to urban areas4. Such migration is esti-
mated to be 70% of the world’s population by 2050 (ref.
5). Urbanization and climate change have a major impact
on watershed hydrology by inducing uncertainty in rain-
fall and run-off patterns1,6,7. Rapid unplanned urbaniza-
tion and increased climate variability pose a serious
threat in the form of urban floods across the globe8. India
is no exception to the growing threat of extreme climatic
events and urbanization problems, whose impacts have
started becoming visible on the ground in the form of ur-
ban flooding events in the last few decades. The recurrent
incidences of catastrophic urban flooding, viz. the Chen-
nai – 2015, Kerala – 2018, Patna – 2019 and Hyderabad –
2020 floods highlight the seriousness of the situation.
Extreme events pose a great challenge towards sustaina-
ble town planning and disaster management9. Consider-
ing the rising urban flood risk, the Government of India
(GoI) has now initiated the Atal Mission for Rejuvenation
and Urban Transformation (AMRUT), programme that
focuses on the provision of water supply, sewerage,
stormwater drains, green spaces and public transport in
500 cities9. The National Disaster Management Authority
(NDMA), GoI, has provided guidelines to tackle urban
floods, but many of these are yet to be implemented in
the field10. The Town and Country Planning Organiza-
tion, Ministry of Housing and Urban Affairs, GoI, has
come out with a standard operating procedure (SOP) for
urban flooding. A manual on stormwater drainage was al-
so published in 2019 for planning sustainable drainage
systems by the Central Public Health and Environmental
Engineering Organization (CPHEEO), Ministry of Hous-
ing and Urban Affairs, GoI11. Despite various initiatives,
urban flooding remains a big challenge due to the rapid
urbanization together with hydrologic extremes and
climate change, towards implementing flood-resilience
measures in many of the cities in India12. The extreme
rainfall events cannot be regulated, but the advancement
in technology allows us to minimize the risk and damage
involved by mapping the extent and severity of such likely
events. The present study analyses the urban floods of
October 2020 in Hyderabad, Telangana, India, from a
geospatial perspective.
Hyderabad has witnessed several devastating floods in
the past, including the disastrous Musi floods which
occurred a century ago in 1908 triggered due to
480.06 mm of rainfall recorded within 48 h, inundating
low-lying areas up to almost 3.3 m and causing massive
damage to life and property13. To tackle floods in the
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CURRENT SCIENCE, VOL. 120, NO. 12, 25 JUNE 2021 1841
Table 1. Recent important flood events in Hyderabad (24-h duration)18,32
Damage/affected areas
Event Rainfall (mm) Deluge depth (m) Lives Houses People (lakh) Estimated loss (Rs)
October 2020 192.0 2–4 81 >20,500 >1.8 5000 crores
September 2019 133.0 1–2 0 >30,000 >1.2 >10 lakhs (goods)
September 2016 167.2 1–2 8 >17,000 >1 60 crores
August 2008 137.0 2–3 14 >32,000 >1.5 49.2 crores
August 2002 130.0 1–2 0 >12,000 >1 >10 lakhs (goods)
August 2001 127.8 1–2 0 >15,000 >1 >10 lakhs (goods)
August 2000 241.5 2–4 26 >35,693 >2 135 crores
July 1989 187.7 1–3 10 >20,500 >1 30 crores
future and provide drinking water to the city two major
reservoirs, i.e. the Osman Sagar and Himayat Sagar were
constructed in 1920 and 1927 respectively14. However,
post-Musi floods Hyderabad has not witnessed similar
amounts of rainfall, but the severity of the problem has
been increasing ever since. The August floods of 2000
(241.5 mm in 24 h) caused huge property loss and more
than 90 residential colonies were submerged (2–4 m
water level). Hyderabad witnessed another intense down-
pour on 13 October 2020, and the event points to the per-
sistent warnings that people chose to overlook over these
years. The low-pressure system that formed in the Bay of
Bengal while crossing over the Telangana region caused
excessive rainfall resulting in massive flooding which
impacted more than 120 colonies, 20,500 homes and
causing as many as 80 deaths15.
Many researchers have studied the aspects of urban
flood hazard for the Hyderabad region16–18. However
most of these studies have focused on reasoning and data
analysis. Few works implemented modelling techniques
using proprietary models and also faced the limitation of
raw data for model-building, development and simula-
tion. The present study intends to capture the geospatial
flooding extent and severity of the event employing the
HEC-RAS 1D–2D flood modelling technique developed
for Zone-12 urban catchment of Hyderabad city for the
13 October 2020 event and compare it with the previous
24 August 2000 event.
Hyderabad: October 2020 urban flooding
Hyderabad experienced continuous heavy incessant rain-
fall during the second week of October 2020, causing
massive flooding in most parts of the city. Generally, for
Hyderabad July–September is the period of peak rainfall
activity, followed by significant decline from October
onwards. However, the recent Hyderabad floods of Octo-
ber 2020 witnessed extreme rainfall which was the high-
est ever in October, and also the second highest on any
day in any month since 1891 (ref. 19). The weather moni-
toring station of India Meteorological Department (IMD)
at Begumpet recorded 192 mm of rainfall during 24 h on
13 October 2020. Before this event, the highest recorded
rainfall in Hyderabad according to IMD was 241.5 mm
on 24 August 2000. Table 1 shows the recent extreme
rainfall events that triggered floods in Hyderabad city and
the damages incurred.
Method and materials
The methodology for carrying out urban flood modelling
in the present study is based on that of Rangari et al.20
adopted for developing a regional-scale urban flood model
with HEC-RAS 1D–2D. It involves hydrologic model
HEC-HMS and hydraulic model HEC-RAS in integration
with ArcGIS 10.1 for Zone-12 of Hyderabad (Figure 1).
The key parameters used for model development and
simulation were rainfall data, stream–drainage network,
catchment characteristics (such as area, imperviousness,
roughness coefficient and elevation), sub-catchment out-
lets, digital elevation model (DEM), 2D flow area and 2D
mesh. The 2D model parameterization is described in
Rangari et al.21. Land use/land cover (LULC) for the
period 2000–2020 for Zone-12 of Hyderabad was used as
base data to perform the model simulation run and assess
the flooding extent. The LULC analysis was performed
using cloud-free Landsat Thematic Mapper (TM) scene
(30 m resolution) acquired on 2 February 2000 and Senti-
nel-2 (10 m resolution) scene acquired on 28 February
2020, through the USGS Earth-Explorer open portal22.
Drainage details (i.e. type of drain, length, size and shape
as well as depth) were acquired from Greater Hyderabad
Municipal Corporation (GHMC). The catchment charac-
teristics were extracted from Cartosat DEM (10 m resolu-
tion) by processing in Arc-GIS. To examine flooding
severity, the model was simulated using rainfall data of
13 October 2020 and the simulation results were matched
with flooding extent of the 22 August 2000 event. The
hourly rainfall data for 13 October 2020 were obtained
from IMD. Monthly rainfall data and cumulative rainfall
depth of extreme events (2000–2019) for the analysis
were taken from open online sources. The daily rainfall
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CURRENT SCIENCE, VOL. 120, NO. 12, 25 JUNE 2021
1842
Figure 1. Location map Zone-12, Hyderabad (source: Google Earth).
data of Hyderabad city (2000–2013) were procured from
IMD. Figure 2 a shows the hyetograph of event rainfalls
considered for model simulation. Figure 2 b presents the
flow chart of the methodology.
Results and discussion
Land-use/land-cover analysis
The satellite imagery was pre-processed to apply the
geometric correction, and suppress the atmospheric effect
and noise in the raw dataset23,24. The nearest neighbour-
hood data resampling was applied to the dataset to match
the spatial resolution of Sentinel-2 and Landsat TM on
account of its clarity and ability to keep store original
information unchanged. The unsupervised ISODATA
technique was employed to classify the land use into four
classes (i.e. built-up area, water body, vegetation and
others). The LULC output was validated by generating
100 random sample points of the developed LULC in
Arc-GIS and exported to Google Earth as a KML layer.
The KML layer was superimposed over the historically
stored images available with Google Earth and a match
accuracy of 87.2% and 88.8% respectively, was observed
(kappa coefficient > 0.83). Kappa value > 0.80 indicates
precision in the approach with a strong agreement25. Fig-
ure 3 shows the changes in LULC of Zone-12, Hyderabad
for 20 years (2000–2020). In false colour composite
satellite images the urban areas appear in steel-grey tone,
vegetated areas in reddish tone and water bodies in dark-
bluish tone. A significant reduction in open land can be
observed with only a few visible pockets of light red
tone, and an overall decline in the number of water
bodies (dark-bluish tone) and their spread. Zone-12
which had 65% of impervious area in 2000 is now almost
89% covered with impervious surfaces, registering an
overall increase of about 23.75%. The increase in imper-
viousness basically in the form of urban growth which has
occurred at the cost of encroachment of vegetative areas,
other open lands and water bodies was 0.95%, 15% and
0.65% respectively. The increased imperviousness limits
the infiltration process thereby increasing the total run-
off from the urbanized catchments up to six times and
peak flows up to 1.8–8 times, thus leading to flooding10.
Flood extent estimation and analysis using
HEC-RAS 1D–2D
The HEC-RAS 1D–2D model derives results in the form
of flood inundation extent and depth with a stipulated
time duration. Figure 4 a shows the progressive ad-
vancement of flooding extent at an interval of 7 h for the
13 October 2020 event. As seen from the figure, around
7 h interval water started accumulating in the areas along
the streamline. The water level started building up with
the passing time that caused the spreading of floodwater
in adjoining low-lying areas at around 14 h. Most of the
localities, including Begumpet, Ameerpet, Madhapur, Tu-
lasi Nagar, Rajiv Gandhi Nagar, Adarsha Nagar, Pragathi
Nagar, Laxmi Nagar and Chandra Nagar experienced
heavy flooding by the end of 21st hour26. A week later,
many of these colonies were still under water27. To have a
comparative analysis of the October 2020 deluge with the
other big flood events which occurred two decades ago,
the flooding extent of August 2000 was plotted over the
flooding extent of October 2020 (Figure 4 b). Figure 4 c
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CURRENT SCIENCE, VOL. 120, NO. 12, 25 JUNE 2021 1843
Figure 2. a, Event rainfall hyetograph for model simulation. b, Flow chart of the methodology.
Figure 3. Changes in land use/land cover over the period of 20 years (2000–2020).
shows the October 2020 flood depth over underlined
terrain. A maximum of 2–3 m inundation depth was
observed at Begumpet, Ameerpet and around Fox-Sagar
Lake. The results show that the rainfall event of October
2020 produced inundation over 34.05 km2 (23.70%),
which is 8.42% more severe compared to the August
2000 inundation (15.28%) (Table 2). From Table 2, we
can observe a more than 50% rise in high risk for the
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CURRENT SCIENCE, VOL. 120, NO. 12, 25 JUNE 2021
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Figure 4. a, Advancement of flood extent with time for the October 2020 event. b, Superimposed flooding extent.
c, The October 2020 flood depth.
October 2020 event. Similarly, there is significant rise in
low and medium risks compared to the August 2000
event. The major affected areas of Zone 12, Hyderabad,
are Begumpet, Ameerpet, Madhapur, Kukatpalli, Rajiv
Gandhi Nagar, Chandra Nagar, Tulasi Nagar and Laxmi
Nagar. The Google Earth projection of the October 2020
flooding presents the extent of risk class and severity of
the event.
Rainfall data analysis
Hyderabad city receives the bulk of its rainfall during the
summer monsoon (June–September) with an average
annual amount of 136.1 mm. Past studies reported no
significant change in the mean monsoon rainfall over the
city, but marked a major rising trend in heavy rainfall at
the end of the summer monsoon15. The vulnerability risk
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CURRENT SCIENCE, VOL. 120, NO. 12, 25 JUNE 2021 1845
Figure 5. a, Hyderabad rainfall data analysis (2001–2019; Source: IMD, online open data). b, One-day maxi-
mum rainfall in October (2001–2020; Source: IMD, online open data).
Table 2. Deluge severity for the flood event
Flooded area (km2)
Deluge risk 13 October 2020 24 August 2000
Low 22.23 14.19
Medium 7.15 5.63
High 4.67 2.13
Total 34.05 21.95
of extreme rainfall conditions on urban catchments can be
addressed by reviewing the severity and seriousness of
past rainfall data. However, the availability of basic data,
including hourly and sub-hourly rainfall data is a major
concern in hydrologic studies. Figure 5 a and b shows the
cumulative monthly rainfall data and one-day maximum
values in October (2001–2019) for Hyderabad city. Based
on the long-term average monthly data of two decades, it
is observed that monsoon is more prominent towards the
end of summer after 2015, and Hyderabad is reeling
under deficit rainfall during June and July. The monthly
rainfall for June and July is observed to be less than the
monthly average rainfall 10 times in the past 20 years.
However, the October monthly average rainfall
(103.6 mm) has been crossed five times in the last 20
years. Further one-day maximum rainfall events show an
increasing trend over the last decade. Such abrupt varia-
tion in rainfall is seen all over the country, and researchers
claim these topical changes in rainfall over the Indian
continent as direct implications of urbanization and
climate change17,28.
Impact of urbanization on land-use changes
One of the reasons for urban flooding is the rapid growth
in population permitting changes in LULC. Studies have
assessed the land-use changes (1972–2013) and the im-
pact of urbanization on rainfall pattern over Hyderabad
city29,30. The population of Hyderabad city has increased
enormously in past 20 years with an average growth rate
of 3.46 (ref. 31), which has exerted a huge pressure on
land use as unbound settlements and is visible through
LULC analysis. Remotely sensed multi-temporal satellite
imagery shows that Zone-12 urbanization has trans-
formed the natural landscape bearing waterbodies, drai-
nage paths, fertile and open lands into a built-up
environment. This transformation has wiped out the iden-
tity of Hyderabad, once known as ‘the City of Lakes’,
with the disappearance of many streams and dried lakes.
The lakes in Hyderabad were connected by a ‘cascade
system’ with a strong natural stream network as the carrier
of floodwater from one lake to another. Figure 6 a shows
the interconnected natural drains that link the series of
lakes through a cascade system. Many of these lakes have
disappeared from the ground, and natural streams
connecting these water bodies are not visible at present
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1846
Figure 6. a, Sentinel-2 satellite image of 28 February 2020. b, Encroachment in lake command area from 2001 to 2020 (source: Google Earth).
due to encroachment and urbanization. Figure 6 b shows
the encroachment in lake command area from 2001 to
2020 (enlarged view of highlighted in Figure 6 a). The
Google Earth projection of lakes shows their reduced
areal extent due to massive encroachments, and its impact
were visible in recent events when the stream path was
activated causing floods, especially in the basement
floors of buildings along natural stream paths and
encroached lake territory. The flooding extent of the
October 2020 event was critically assessed and analysed
to be compared with the August 2000 event. Though the
October 2020 event was less critical, it has produced
8.42% more flooding extent and vast damage in terms of
property and human life compared to the more severe
event of August 2000. Thus, to summarize, the October
2020 Hyderabad flood event and the resulting damage are
an aggregation of climate change, changes in rainfall pat-
tern, uncontrolled urbanization and land-use changes in-
duced to anthropogenic activities. Since urbanization and
climate change go hand-in-hand together, urban flooding
and the subsequent damage will intensify in the near
future. Therefore, to make cities resilient to urban flood-
ing, we must adopt flood-mitigation measures, rejuvenate
natural wetlands, upgrade the storm sewer drainage in
tandem with future population-projected scenarios, adopt-
ing nature-friendly engineering solutions as an integral
part of the smart-city planning.
Conclusion
The selection of a particular model for urban flood situa-
tions is a complex task and needs to be tackled delicately
based on the requirement of model input parameters,
availability of extensive dataset and output deliverables.
This study presents an HEC-RAS 1D–2D urban flood
modelling approach to assess geospatial flooding extent
and risk analysis. The model simulation results are
presented as spatial flood extent and risk maps that show
the susceptibility of the study area to flooding events and
the associated risks. These maps can be used by the city
administration, governing authorities, and common
people to identify critical areas during extreme events and
find safe places of shelter. The maps will also help the
urban planners in sustainable future developments. Fur-
ther, the study highlights the fact that even though the
October 2020 event (191.1 mm) was less severe in terms
of rainfall than the August 2000 event which saw higher
rainfall, rapid urbanization (16.5% increase) over the last
two decades has increased the flood severity. Therefore,
urbanization needs to be regulated and equally supported
with adequate capacity for stormwater drains to address
the increased population. The water bodies and streams
need to be rejuvenated so that they can absorb the excess
flow during monsoon season. Proper regulations and their
strict implementation are necessary against the encro-
achment of water bodies. Satellite images in conjunction
with geospatial technologies and hydrological models can
be useful in assessing such events and planning mitiga-
tion measures.
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ACKNOWLEDGEMENTS. We thank IMD for sharing event rainfall
data. We thank Greater Hyderabad Municipal Corporation (GHMC)
and M/S Voyant’s Solutions Private Limited, Hyderabad for sharing
technical data. We also thank National Remote Sensing Centre (NRSC)
for high resolution dataset to take the study forward. The Landsat satel-
lite images are downloaded from the United States Geological Survey.
We also thank to HEC-RAS technical team for their valuable sugges-
tions and technical support.
Received 16 January 2021; revised accepted 21 March 2021
doi: 10.18520/cs/v120/i12/1840-1847
