Analytical Study of North Indian Oceanic Cyclonic Disturbances with Special Reference to Extremely Severe Cyclonic Storm Fani: Meteorological Variability, India’s Preparedness with Terrible Aftermath

Having a total coastal tract of about 7,516 km with 5,400 km long mainland coastline, India is highly vulnerable to natural hazards like tropical cyclones (TCs). The analysis based on the historical dataset (1891-2019) of TCs over North Indian Ocean (NIO) also claims that the four coastal states (Andhra Pradesh, Odisha, Tamil Nadu and West Bengal) and one 10 union territory (Pondicherry) on the east coast frequently face cyclonic storm than other coastal parts of India. The seasonal distribution (Pre-monsoon, Monsoon and Post-monsoon) of cyclonic storms over the Arabian Sea (AS) and Bay of Bengal (BoB) in last 150 years also help to unfold the fact that the Odisha and West Bengal coast are exposed to TCs mostly during the monsoon season (June to September) encompassing with strong winds, heavy rainfall and high storm surge. The extremely severe cyclonic storm (ESCS) Fani is the rarest summer cyclones, the first one in 43 years to strike the coastal part 15 of Odisha on May 3, 2019 and one of the three worst cyclones in last 150 years with a sustained surface wind speed of 175180 kmph. Odisha has been affected horribly due to the vulnerability of Fani. Although the death toll was limited within 64 due to rapid evacuation of nearly 1.68 million people, the killer cyclone has caused irreparable damages in social sectors (housing, education and food security), productive sectors (agriculture, fisheries and livestock) and also informative sectors (power, telecommunication, road, water facilities and public buildings). The estimated costs have reached nearly 4.18 billion 20 USD only in Odisha. The southern part of West Bengal has also affected badly due to intense downpour and very high storm surges (2-3 m above mean sea level). To map the flooded areas of Odisha and West Bengal due to intense rainfall (cause inland flooding) and storm surges (cause coastal flooding), the Sentinel-1 SAR GRD dataset has also been used in Google Earth Engine (GEE) environment to link with the deadly cyclone Fani. So, the present study successfully advocates the historical background of TCs over NIO with particular reference to ESCS Fani including its meteorological variability, 25 preparedness and the trail of devastation. https://doi.org/10.5194/nhess-2020-287 Preprint. Discussion started: 23 September 2020 c © Author(s) 2020. CC BY 4.0 License.


Introduction
Tropical cyclones (TCs), one of the biggest threats to life and property have caused 0.77 million death and 1,407.6 billion USD economic loss worldwide in last fifty years with an average of 43 deaths and 78 million USD damages every day (WMO, 2020). India is not far behind in this regard for having about 5,400 km long mainland coastline out of total 7,516 km 30 coastal tract (Mohapatra, 2015;Mohapatra et al., 2012;NCRMP, 2019). So, the country is also highly vulnerable to the natural hazard like TCs which are originated in the North Indian Ocean (the Arabian Sea and Bay of Bengal), although the region generates only 7 % of the world's TC (Dube et al. 1997;Mohapatra, 2015). Out of 96 cyclone-affected districts of India (including 72 coastal districts), 12, 41, 30 and 13 districts come under very high, high, moderate and less cyclone hazard-prone categories, respectively (Mohapatra et al., 2012;RSMC, 2018a), based on the frequency of total cyclones and 35 severe cyclones, actual/estimated maximum wind strength, Probable Maximum Storm Surge (PMSS) and Probable Maximum Precipitation (PMP). Besides, the studies of Dube et al. (1997), Mohapatra (2015), Mohapatra et al. (2012) and RSMC (2018) also claim that almost all the coastal districts of West Bengal, Odisha, Andhra Pradesh and Tamil Nadu come under high to very high cyclone hazard-prone category because the majority of cyclones occur in Bay of Bengal (BoB) as The year, 2019 has experienced four very severe or more intense cyclonic storms, but the Extremely Severe Cyclonic Storm (ESCS) Fani is the only tropical cyclone of the year that has made landfall as a very severe cyclonic storm in the coastal part of Odisha (Puri district) on 3 May (RSMC, 2020). It is also the strongest TC to strike Odisha coast since 1999 super cyclone 45 not only in terms of intensity but also from the perspective of damage in social sectors (housing, education and food security), productive sectors (agriculture, fisheries and livestock) and also informative sectors (power, telecommunication, road, water facilities and public buildings). Despite taking several pre-storm emergency preparedness plans, ESCS Fani has succeeded to cause large damage of an estimated cost of 4.18 billion USD only within Odisha (India) with 64 human casualty (OSDMA, UN India, WB and ADB, 2019;UNICEF, 2019). So, the present study has focused on the detailed 50 scenario of cyclonic storm distribution over North Indian Ocean (NIO) and trend analysis from 1891 to 2018 with particular reference to Fani and its devastating impact on lives, property and economy due to high-speed winds, excessive rainfall, storm surge and flooding.

Historical background of cyclonic disturbances
The states like Andhra Pradesh, Odisha and West Bengal situated along the eastern coast of India have experienced severe 55 damages due to TCs originated in the BoB (Chittibabu et al., 2004;Dube et al. 1997;Dube et al. 2000aDube et al. , 2000bMohapatra, 2015;Mohapatra et al., 2012;Rao et al., 2006) because the most of the cyclonic storms tend to occur in the BoB basin as compared to the AS basin with an approximate ratio of 3:1. Naturally, the prepared gridded image (Figure 1a) based on the https://doi.org/10.5194/nhess-2020-287 Preprint. Discussion started: 23 September 2020 c Author(s) 2020. CC BY 4.0 License. genesis of cyclonic storms data over NIO basin by Indian Meteorological Department (IMD) indicates that the BoB has experienced very high frequency of cyclonic storms cumulatively since 1891. On the other hand, the inter-annual average 60 values of the past 128 years (1891-2019) also specify that the BoB experiences almost 2 severe or more intense cyclonic storms out of every 6 TCs, whereas the AS originates almost 1 severe or more intense cyclonic storms out of every 2 TCs. So, the above discussion helps to understand the reason behind belonging of the coastal tract of northern Bay of Bengal to the very highly vulnerable cyclone hazard-prone zone with having potentiality to generate high storm surge and killer strong gusty winds. The further analysis (Figure 1b) also explains that the most of the TCs in the lower latitudes in association with 65 Inter-tropical Convergence Zone (ITCZ) occur during pre-monsoon (March-May) and post-monsoon (October -December) seasons, but the coastal states along with the northern BoB and AS have faced most the cyclonic storms during monsoon season (June -September). So, the high-intensity devastating summer cyclone is the rarest event in the long cyclonic history of northern BoB.
Extensive work has been also done by Mooley (1980), Singh et al. (2000Singh et al. ( , 2001, Singh (2007), Srivastava et al. (2000) and 70 Mohapatra et al. (2017) for determining the change analysis in the intensity and frequency distribution of TCs over BoB and AS. In the present study, the temporal frequency distribution data (1891 -2019) of cyclonic disturbances by IMD (RSMC, 2019) has been analyzed for obtaining long-term trend of TCs over NIO. The analysis also helps to unfold the fact that the 30 years moving average lines of overall cyclonic storms and severe or more intense TCs almost follow the constructed regression lines for the period of 1891 to 2019 (Figure 2a). To analyze the historical trend of TCs in more detail, the 75 intensification rate of cyclonic storms to severe or more intense cyclonic storms has been examined over BoB and AS for the past 128 years. The results (trend lines in Figure 2b & 2c) help to understand that the changes in the intensification rate of cyclonic storms to severe or more intense TCs have increased over time in case of both the BoB and AS with the R 2 values of 0.0985 and 0.0054, respectively.
The coastal districts of Odisha have experienced several cyclonic storms with strong winds, floodings and very high storm 80 surges, but Fani is the rarest summer cyclones, the first in 43 years and one of the three worst cyclones in last 150 years to strike the coastal part of Odisha with immense economic and social impact (OSDMA, UN India, WB and ADB, 2019; UNICEF, 2019). Then it further proceeds towards West Bengal and finally weakens over Bangladesh and its adjoining Indian territory (Central Assam).

Data used and methods 85
Large numerical datasets, pre-storm & post-storm images and extensive study are required for analyzing the historical background of TCs over NIO, the meteorological overview of ESCS Fani (wind speed data, atmospheric pressure data, rainfall details & storm surge information) and damage details including inundation statistics with causality due to the devastation caused by the cyclone Fani. The data related to the frequencies of TCs over the BoB and the AS for the period of association with IMD. Two types of images (Table 1) Table   3. Based on the available information, it can be claimed that the present study has its significance in terms of subject matter because no discussion has been made so far in any study where the coastal and inland flooded zones have been delineated with the calculation of inundation statistics due to heavy rainfall and storm surge during cyclone Fani. Besides, this is the 115 only article where India's preparedness and damage statistics have also discussed briefly in the context of cyclonic storm Fani with the long historical background of TCs over the NIO.

Synoptic history of ESCS Fani
The cyclonic storm Fani has covered long distance (nearly 3090 km) combinedly over the Bay of Bengal, Indian and  Table 4.
The meteorological observations include the sustained wind speed and also the atmospheric pressure ( Figure 5) during the storm event. Fani's maximum wind speed of nearly 213 kmph has occurred over NW BoB just fifteen hours before of 140 making landfall on the Odisha coast at 20:30 hrs IST on May 2. The minimum pressure of cyclonic storm Fani has been estimated to be 932 hPa on that particular day. On the other hand, the maximum wind speed has observed nearly 157 kmph with 966 hPa atmospheric pressure (the lowest estimated central pressure after making landfall) at the time of striking Puri, one of the coastal districts of Odisha at 11:30 hrs IST on May 3. The correlation coefficient value (r) is indicating the strong negative relationship (-0.98) between two weather variables (wind speed and atmospheric pressure) which are collected 145 along the best track of summer cyclonic storm Fani.

Results and Discussion
This particular section of the study includes three main aspects which are intimately related to cyclonic storm Fani, viz., India's preparedness, inundation details and other damage statistics. The first one (disaster preparedness) helps to understand how India has abled to tackle and overcome the situation by taking management proper steps and keeping the death toll in 150 control. Last two aspects (inundation details with other damage statistics) help to get the idea about the devastation caused by ESCS Fani, in spite of taking the necessary steps to handle the cyclone situation.

India's preparedness
The pre-storm and post-storm disaster preparedness programmes always create several challenging situations for the country like India, the world's second-most populous land with 1,366 million residents (United Nations, 2019). In case of the tropical 155 cyclone, the coastal districts of India have to face more critical situations for having high population density. Nearly 40% of the total population is more or less exposed to cyclones because of living within 100 km of coastline in India (NCRMP, 2019). The strong winds with heavy rainfall and storm surge during cyclonic storms can cause severe damage that includes complete or partial destruction of homes, buildings, roads, power connections and water outages (FEMA, 2017). So, the proper pre-storm emergency preparedness plan takes an important role to reduce the damages and casualties caused by an 160 unavoidable disaster like the tropical cyclone.

Inundation detail
Effective monitoring of floods is quite impossible without the use of satellite images. GEE has made the work easier than before as because of its capabilities to detect temporal changes on the earth's surface (Uddin et al., 2019;DeVries et al., 2020;Agnihotri et al., 2019;Clement et al., 2017;Kussul et al., 2011) using the Sentinel-1's C-band SAR active sensor https://doi.org/10.5194/nhess-2020-287 Preprint. Discussion started: 23 September 2020 c Author(s) 2020. CC BY 4.0 License. derived images, an independent dataset of any time of the day or night, regardless of weather and environmental conditions 185 (ESA, 2020). So this particular cloud-based platform has been used for monitoring flood situation due to heavy rainfall (responsible for inland flooding) and storm surge (caused coastal inundation) during ESCS Fani.
The rainfall associated with ESCS Fani based on daily accumulated precipitation extracted from GPM IMERG Final Precipitation (0.1 degree x 0.1 degree, V06) data in Giovanni environment has been represented in Figure 6 from April 26 to The cyclone affected regions of Odisha and West Bengal have been divided into five equal width zones (15 km each) based on the distance from the coast (Figure 7) for the more detailed explanation, but it doesn't signify that any inundation has not occurred beyond that extent. The results derived from the analysis of the SAR images in GEE environment (Table 5) help to  205 understand the overall flood scenario over the major affected regions due to heavy rainfall and powerful storm surge. The computed inundation statistics claim that Puri, one of the coastal district of Odisha has faced major flooding due to a large amount of rainfall with a high level of storm surge during the storm event. Besides, the other parts of the first zone (0-15 km) within Odisha have also experienced large inundation than other zones due to the heavy downpour and moderate to low-level storm surge because the advancement of ESCS Fani has occurred towards the Gangetic West Bengal almost along the 210 coastal tract of Odisha. On the other hand, the coastal tract of West Bengal has faced a significant inundation for experiencing high to low-level of storm surge with heavy rainfall. The statistics also claims that the highest amount of inundation has occurred in the fourth zone (45-60 km) of West Bengal than other parts of the cyclone-affected regions because the summer cyclone Fani has moved towards Bangladesh through this zone and has caused heavy rainstorm on May 3, 2019. Figure 8 helps to get a better view of the most affected regions due to inundation during cyclonic storm Fani over 215 Odisha and West Bengal. https://doi.org/10.5194/nhess-2020-287 Preprint. Discussion started: 23 September 2020 c Author(s) 2020. CC BY 4.0 License.

Other damage statistics
If the flooding has been explained as the only consequence of the devastating tropical cyclone, the severity of the storm will be underestimated. The intensive rainfall, strong winds and storm surges cause several other damages during storm event across the world, making the coastal people vulnerable to cyclone (Khalil, 1993;Wang and Xu, 2008;Li and Li, 2013;Ward 220 et al., 2011;Done et al., 2018;Mori and Takemi, 2016). The deadly cyclonic storm Fani has also unleashed copious rainfall with the powerful windstorm that has gusted up to 205 kmph, leading to fatalities, complete destruction of kutcha houses, partial damage to buildings and others properties like roads, power sectors, health care centres, educational sector,

embankment, etc. The trail of devastation caused by ESCS Fani in the large part of Odisha with West Bengal and Andhra
Pradesh has been explained briefly in Table 6. 225

Conclusion
The present study has focused on the historical background (1891-2019) of TCs over NIO with particular reference to ESCS Fani with meteorological variability, India's preparedness and awful aftermath. The discussion helps to understand that the probabilities of intensification of a cyclonic storm into a severe or more intense cyclone over the northern BoB and AS is maximum during the monsoon season (June to September), differs from the intensification period of the cyclones that 230 originate over the southern BoB and AS mainly during pre-monsoon (March to May) and post-monsoon (October to December) seasons. The recent work also confirms that the Utkal (Odisha), Bengal and Andhra coast receive higher frequency of TC than any other coastal tracts of India. Fani, one of the three worst cyclonic storms in last 150 years during pre-monsoon season has made landfall near Puri of Odisha coast and causes devastation over the extensive parts of mainly Odisha and West Bengal, in spite of taking zero casualty approach by the local and national government. Generally, there are 235 two possible ways of obtaining the complete resilience against such intense TCs, namely, the pre-storm preparedness plans understanding the risk based on early warning and also resilient infrastructure. India has already abled to achieve its first goal. IMD has made the work easier for the Indian government. But it is quite impossible to manage the second goal, resilient infrastructure for every citizen in a highly populous country like India. For that reason, the government has to build sufficient cyclone and flood shelters so that evacuated people get protection during the storm event and the death toll can be 240 reduced. The several state-level housing schemes and national housing schemes like Indira Awas Yojana (IAY) and Pradhan Mantri Awas Yojana (PMAY) for the economically weaker section can also cause the advancement towards a long-term solution to ensure full resilience against cyclonic storms slowly. So India can't get off immediately from the massive economic losses caused by TCs almost every year until the nation becomes successful to achieve the final goal with time.