Introduction & Study Area
A monsoon is a seasonal change of winds in several tropical areas of the world.
Monsoons are usually accompanied by precipitation because it is a change of wind
direction from ocean to land instead of land to ocean as it is normally. (McGregor, 121)
One of the more known monsoons is the Indian monsoon. The Indian monsoon brings a
lot of rain to the country but is always variable in the amount and distribution of rain for
the country. The monsoons variability can affect Indiaʼs people and economy because
many people rely on this water supply for their agriculture which will be devastated if
they do not get it. High amounts of rain can also bring flood risks to several areas in
India. (BBC)
Assessing possible flood risk areas can be helpful for these people so that they
can take safety precautions to avoid damages and death. People living near streams
and rivers may have higher chances of being affected which is not good because more
people tend to live here due to the availability of water, a required resource for survival.
India is located in Asia and has the worlds second largest population. (Population of All
Countries of the World Largest to Smallest) India also contains several rivers and
streams, the largest and more known of which is the Ganges River located in the North.
The Southern portion of India is surrounded by the ocean while the northern portion
borders several countries and part of the Himalaya Mountains.
Methodology
In order to preform an analysis on possible flood risk zones in India I first took a
look at several aspects which may affect the risk. First I decided to do an interpolation of
the average precipitation values of July from 1961-1990. The first step for my
interpolation was finding data for precipitation in India. Once I found the data, I decided
to use the averages for July because it seems to be the month with the most activity in
terms of rain. I made an excel sheet for several cities throughout India trying to reach
the farthest extents I could. I then researched their latitudes and longitudes in decimal
degrees to add the data into arc-map. Finally I added in the averaged precipitation
values. Once I added the data in the X,Y format, I used the Spatial Analyst tool to
perform the interpolation using the IDW method.
My second step in assessing possible flood zones was looking at the elevation of
India. I downloaded a raster DEM from Diva-GIS which I displayed using the symbology
tab under properties. I decided to display the DEM under 6 classes in the geometric
classification to better view the elevation and understand the elevation of areas. Areas
with lower elevation would be at higher risk than those in lower elevations because
water flows downhill. This will be taken into account later on in the analysis.
The third aspect I took a look at was the accumulation flow of streams and rivers
in India. To preform this I used the symbology classified tab and used the flow
accumulation of streams as the value to be classified. I used a total of 9 classes ranging
from blue for low accumulation to red for high accumulation with yellow as the
intermediate. I then found the threshold (120,000 cells) for which the accumulation
starts to be significant. I then selected these lines and created a shape-file to display the
Med-High Accumulation so that I could later overlay them on other maps.
The fourth step I took in assessing flood risk zones was analyzing the drainage
basins to see which areas may be affected. I decided to first merge all the basins to see
the relationship between the merged basins and the rivers. I then overlaid the shape-file
I made for the significant accumulation flow streams on the layer of individual basins to
later do a select by location. I selected the individual basins that intersect with the
accumulation layer and exported them into another shape-file for the High Risk Basin
Accumulation layer.
The final step of my analysis was creating a map displaying the population and
which areas are at a higher risk for floods. I obtained a population raster data-set which
I classified into 7 classes in the geometric classification. I then overlaid the significant
flow accumulation layer followed by the High Risk Basin Accumulation layer which I
hollowed out so we can see the relative population within these areas. I then used the
extract by mask spatial analyst tool to extract the population information of the areas
within the High Risk Basin Accumulation layer to find out statistics of the population
living within the risk zones.
Results
Below are the five maps I produced showing the different information I derived
from my data sets. A brief analysis on the information displayed is given for each map.
The first map is the interpolation of the rain averages for July from 1961-1990. As
noted before, I chose this month because it shows the most activity during the monsoon
season of India. The map shows us that there is more rain in the southwestern portion
of India which makes sense because this is where a portion of the winds come, bringing
the rain with it since it is located next to the ocean.(McGregor, 125) Here we can see
the streams that are located within the areas of higher precipitation and how they may
affect the flood risk based on their location.
The next map is the elevation map with the Med-High Flow Accumulation
streams layer. Here we can see the areas that have a higher chance of being flooded
based on the accumulation flow and the elevation. Areas in lower elevations are more
susceptible to flooding because water flows downhill. Here we can see that the streams
with the higher possible accumulations are located in the lower elevations partly
because of this reason. We can also see how the elevation changes gradually getting
lower as it moves towards the ocean, the same direction that the rivers flow.
which streams have a higher accumulation of water flow as they flow downstream. The
largest river with a significant amount of flow accumulation is the Ganges River in the
North which makes sense because it has many tributaries flowing into it. One of the
streams connected to the Ganges also has a significant amount of flow accumulation
risk, the Ghaghara. To the West of the Ganges, the Brahmaputra is another river which
may pose a threat for flooding in India as well as a small portion of the Luni located on
the eastern coast of India. Moving South from the Ganges, the Mahanadi, the Godavari,
and the Krishna also have a significant amount of accumulation flow which may pose a
threat of flooding for these areas as well.
The fourth map shows us the individual drainage basins that are at a higher risk
of flooding during the monsoon season because they are within the path of these
streams and rivers. Most of the areas at risk are located on the Northern and Western
part of India which when looking at the fifth map, population, is where a majority of the
population lives.
According to the statistics calculated of the population living within the basins
with higher flood risk is approximately 1,309,897 people. This makes sense because a
lot of people live nearby water systems because they depend on the water for survival.
Conclusion
In conclusion, according to the data and my analysis, several areas in India have
a risk of flooding due to their elevation, flow accumulation, and drainage basins.
Together, these areas have a population of about 1,309,897 people which are at greater
risk of having damage to their property, injuries, and even death due to flooding during
the monsoon season. Many of these people live near these bodies of water because
they depend on the water for agriculture and other needs so something should be done
to better protect these people from flooding hazards. Relocation of the population
seems like a good idea, but these people would just over extract ground water or create
more environmental degradation in other areas. More dams or better management of
dams would also be a good idea, but it may also bring more conflicts because the
people upstream would have more control over the water in dryer periods and the water
would not be equally distributed for those living downstream where the danger is. At the
moment, it seems that the best thing to do is just have better management of the
existing dams.
References
"Geography Facts about India." Geography Facts about India. N.p., n.d. Web. 19 Sept. 2012.
<http://www.facts-about-india.com/Geography-facts-about-india.php>.
"India Monsoon Floods Kill 34 in Uttarakhand." BBC News. BBC, 08 June 2012. Web. 19 Sept.
2012. <http://www.bbc.co.uk/news/world-asia-india-19144580>.
McGregor, Glenn R., and S. Nieuwolt. Tropical Climatology: An Introduction to the Climates of
the Low Latitudes. New York: Wiley, 1998. Print.
"Population of All Countries of the World Largest to Smallest." Population of All Countries of
the World Largest to Smallest. N.p., n.d. Web. 19 Sept. 2012.
<http://www.worldatlas.com/aatlas/populations/ctypopls.htm>.
"Providing Science and Imagery to Better Understand Our Earth." USGS/EROS âÿº -Home.
N.p., n.d. Web. 19 Sept. 2012. <http://eros.usgs.gov/>.
"Spatial Data Download." DIVA-GIS. N.p., n.d. Web. 19 Sept. 2012.
<http://www.diva-gis.org/datadown>.
"World Weather Information Service - India." World Weather Information Service - India. N.p.,
n.d. Web. 19 Sept. 2012. <http://www.worldweather.org/066/m066.htm>.
Drainage Basin Information & Shapefile, Instructor Provided, Jida Wang Sept. 2012
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