Appraisal of climate change and cyclone trends in Indian coastal states: a systematic approach towards climate action

Indian coastal regions have often been affected by frequent climate-induced natural disasters such as cyclones, floods, droughts and other related hazards in recent decades. Existing literature was not sufficient to fully understand these event trends from diverse perspectives in a systematised manner at current scenarios. Therefore, a systematic approach has been employed to assess the climate change and cyclone trends of nine Indian coastal states by using various geographical information system (GIS) tools for 2006–2020. The results showed that 61 cyclones occurred in nine coastal states from 2006 to 2020; the highest numbers were recorded in Odisha (20), West Bengal (14) and Andhra Pradesh (11). Accordingly, these three coastal states emerged as the most vulnerable for high-intensity cyclones. The results also identified that the highest average temperature (29.3 °C) was recorded at Tamil Nadu and Gujarat, and the lowest temperature (26.7 °C) was recorded in West Bengal and Odisha. Most of the coastal states showed fluctuations in temperatures during the study period. At the same time, Kerala and Karnataka states recorded the highest average rainfall (2341 mm and 2261 mm) and highest relative humidity (78.11% and 76.57%). Conversely, the Gujarat and West Bengal states recorded the lowest relative humidity at 59.65% and 70.78%. Based on these results, the current study generated GIS vulnerability maps for climate change and cyclone activity, allowing one to rank each state’s vulnerability. Cumulatively, these results and maps assist in understanding the driving mechanisms of climate change, cyclones and will contribute towards more effective and efficient sustainable disaster management in the future.


Introduction
Coastal states of India are often affected by frequent climate induced natural disasters such as cyclones, floods, droughts and other related hazards in recent years (Mirza 2003;Patel et al. 2020; Thomalla and Schmuck 2004;Yadav and Barve 2017). Climate change is having a significant impact in tropical and subtropical countries, especially coastal regions. Coastal areas in some countries particularly in the global south are highly susceptible to the various impacts of climate change due to anthropogenic and natural climatic factors (Bouwer 2011;DasGupta and Shaw 2013;Nath and Behera 2011;Sivakumar and Stefanski 2010). Severe changes in climatic and weather conditions, rapid sea-level rise (SLR), storm surge, temperature fluctuations and irregular rainfall trends have increased coastal vulnerability problems in the majority of coastal regions across the globe, resulting in huge losses of coastlines, properties and damage to coastal communities (Burkett 2012; Gupta et al. 2019;Lal 2003;Mimura 2013;Sánchez-Arcilla et al. 2011). Likewise, many coastal states of India suffer severe cyclonic storms leading to flooding. Furthermore, some of these coastal states are particularly highly populated: Maharashtra, West Bengal, Tamil Nadu, Karnataka, Andhra Pradesh, and Gujarat states' coastal communities have been highly impacted by climate change and cyclones (Baig et al. 2020;Kantamaneni et al. 2019;Mazumdar and Paul 2016;Rao et al. 2020a;Rehman et al. 2020). The rapid urbanisation increases the risk of pluvial floods in the coastal areas (Zhang et al. 2018;Zhu et al. 2021Zhu et al. , 2015, and the impact of climate change on coastal states is a serious concern. Tropical cyclones are one of the greatest threats to human life and property even during the initial stages of cyclonic development. In the last 50 years, 1, 942 disasters have been identified as tropical cyclones, killing 77,9324 people and causing $1,407.6 billion fiscal destruction across the world (World Meteorological Organisation 2021). Nearly, 630 million people will live below estimated annual flood levels for 2100; 1 hundred million people live below high tide areas globally (Kulp and Strauss 2019), and the number of high intensity global tropical cyclones will likely rise due to anthropogenic global warming in the twenty-first century (GFDL -Geophysical Fluid Dynamics Laboratory 2021). The different downscaling and Multiple Earth System Models (Emanuel 2017(Emanuel , 2021Irvine et al. 2019;Knutson et al. 2020;Michaelis and Lackmann 2019;Patricola and Wehner 2018;Wehner et al. 2014) forecast that anthropogenic climate change will increase the frequency and intensity of the most intense tropical cyclones and amount of rainfall (Irvine et al. 2019). The warmer sea surface temperature has resulted in large stocks of moisture and the intensification of cyclones which hit land. Over the past 50 years, the number of landfalling hurricanes in the North Atlantic has increased by 94% (Michaelis and Lackmann 2019), and East Asia and North West Pacific have experienced an increasing trend in rapid intensification of tropical cyclones with an escalated cost of destructions (Basconcillo and Moon 2022;Chan et al. 2021;Liu and Chan 2022).
The changes in global sectoral interactions in several countries due to tropical cyclones over the period of 1990-2015 show that tropical cyclones have a substantial adverse effect on the yearly growth rate of almost all sectors. Damage to productive capital, infrastructure, or buildings can have direct negative consequences and lead to a negative income shock for the entire economy (Kousky 2012). The intensification of tropical cyclones due to global warming exposes more people to it and also intensifies the future cost of climate change (Kunze 2021). The extreme weather events in 2020 caused significant damage to the economies in several countries across the globe particularly in Asian Countries such as China (USS238), India (USS87), and Japan (USS83) (WMO-World Meterological Organisation 2021).
The Indian Ocean area is one of the 6 most prone cyclone areas in the world with five to six cyclones on average per year (Sahoo and Bhaskaran 2018). Indian coastal regions with low-lying terrain, high population density, frequent cyclones and storms, and a high rate of coastal environmental degradation lead to many disasters and extreme vulnerability for the coastal states. In the Indian region, more cyclones occur in the Bay of Bengal than in the Arabian Sea at a ratio of 4:1 (Rao et al. 2020b). Many different types of coastal ecosystems can be found along the Indian coastline, i.e. coastal wetlands, major estuaries, lagoons, and mangroves. Total coastal wetland covers 43, 230 km 2 of the coastal states; 97 major estuaries and 34 major lagoons are found throughout the study area; 31 mangrove areas are located on the coastline and total mangrove areas covered 6740 km 2 , where 57% of mangrove areas are situated the East coast, and 23% of the area covered along the West coast and 20% of the mangroves area is located at the Andaman and Nicobar Islands (Central Marine Fisheries Research Institute 2021). The coastal states have tropical climates and monsoons with a dry and rainy season. The rains are more or less intense and long-lasting depending on the area (Nandargi and Mulye 2012).
Frequent occurrence of cyclones is very common in the Indian coast and causes heavy damage resulting from the effects of storm surges and high tides (Rao et al. 2020b;Shaji et al. 2014;Unnikrishnan et al. 2006). Estimated sealevel projections for future years and centuries indicate the potential exposure of the coastal population to the various hazards; coastal planning is vital for further improvement of adaption strategies. Additionally, three megacities are located on the Indian coastline, i.e. Mumbai, Kolkata, and Chennai, and some growing cities with millions of inhabitants are at high risk. Furthermore, the impact of climate change is reflected in sea surface temperatures and tropical storm characteristics which are increasing every year. India (coastal cities) has been chosen as a research area as one of the tropical countries in South Asia; however, the existing literature was not sufficient to fully understand these events' trends in coastal areas from diverse perspectives. Therefore, the current study examines climate change and cyclone trends in 9 coastal states. Also, this research address the UN-SDG (United Nations Sustainability Goal) 13 (climate change) by doing the above mentioned assessments in diverse ways. Consequently, this research explains how climate change will be a barrier to achieve SDG 13 in coastal states of India and offer some guidelines to overcome the problem. The changing environment and climatic conditions and the increasing number of extreme events (such as frequent floods, droughts, cyclones and other related disasters) push millions of people into chronic poverty worldwide. This increases the imbalances in physical, social and economic systems and affects sustainable development. It disturbs various economic activities, including agriculture, food safety and tourism. It threatens the very existence of island counties and coastal cities. Different research findings proved the effects of climate vulnerability on vectorborne diseases. Increasing sea surface temperature raises coastal vulnerability. Overall, it has a significant impact on the Sustainable Development Goals (SDGs), which we plan to achieve by 2030. Though SDG 13 focuses on combating climate change and its impacts, and national governments are taking various steps to build climate-change-resilient communities, climate change is still a great challenge and an impediment to achieving all the other SDGs. These results will help for future planning and policy making and efficient sustainable coastal management.

Study area
India is the seventh-largest country in the world by area (3.28 million sq. km) and the second-largest by population (1.3 billion), with 28 states and 8 union territories (Government of India 2022). It occupies a significant portion of the South Asian subcontinent, which has nine coastal states and two coastal union territories. These states' boundaries occupy the Bay of Bengal, the Arabian Sea and the Indian Ocean as shown in Fig. 1. The total length of the coastline is 7, 516.6 km, comprising the mainland with 5, 422.6 km and island territories of 2094 km (Table 1). The exclusive economic zone (the areas identified as economically beneficial) is an identified 2.02 × 106 million km2, and three states include megacities with the largest population pressure, i.e. Maharashtra, West Bengal and Tamil Nadu. The total population of coastal states and union territories is 560 million, and it comprises 46.2% of the total population Singh 2003). The inland consists of four areas called the plains of the Ganga and the Indus (1), the great mountain zone (2), the desert region (3) and the southern peninsula (4). India is a tropical country with hot to extremely hot weather in summers and dry winters with four main periods per year called winter (December-February), summer (March-June), pre-monsoon season (June-September) and post-monsoon season (October-November) (Government of India 2022). However, significant changes have been recorded in these four seasons -extended hot summers and shortened winters.
According to the NDMA (National Disaster Management Authority), in 2022, 75% of the Indian coastline is susceptible to cyclones and related hazards. More than 60 districts and > 14% of the coastal states and the population of the union territories are frequently exposed to different levels of cyclones. Though 7% of global cyclones originate in the Arabian Sea and the Bay of Bengal, the impact of cyclones on Indian coastal states is enormous. The geography of India and the fluctuations in climatic conditions (temperature, rainfall trends, humidity, etc.) are vital factors that lead to an increase in the intensity and frequency of cyclones and in the damage inflicted on the coastal areas of India. Among all natural disasters, cyclones contributed to 15% of the total number of natural disasters that occurred in India between 1999 and 2020, and they rank third after floods and earthquakes (Government of India 2022). Based on these reasons, nine Indian coastal states (excluding two union territories) have been selected for the assessment to offer updated knowledge on climate changes and cyclone trends.

Data
The current study adopted the Donnadieu et al. (2017)'s systematic approach to assess climate change and the cyclone trends in Indian coastal states. This systematic approach accumulates all the empirical evidence that is related to corresponding research, and it has been considered the answer to an explicit research question. Besides, the systematic approach method reduces bias and leads to more trustworthy findings for decision-making. Accordingly, a systematic approach has been used to assess the trends of climate change and cyclones in a logical order to offer updated knowledge. The present research is an appraisal of historical climatic data (temperature, rainfall and relative humidity) in relation to cyclone intensity. The data was acquired from NASA Power Data Access (https:// power. larc. nasa. gov/ data-access-viewer/) and NASA Langley Research Center. Temperature and humidity were measured 2 m above the surface. Correspondingly, the data about cyclones (Table 1) was gathered from IMD E-atlas, the Indian Meteorological Department, and was divided into three categories based on the intensity (i.e. depressions [D], cyclonic storms [CS] and severe cyclonic storms [SCS]). The current study analysed the spatial exhibitions of the cyclone-prone areas and the spatial exhibitions of the cyclonic paths using the 'Display XY Data' GIS tools -ArcGIS 10.6. Temperature, rainfall, and humidity data were constructed annually to reveal the in-depth climatic changes of Indian coastal states (Table 2).

Analysis
The study categorised the cyclones into three types based upon the intensity derived from the criteria-based classification, Indian Meteorological Department, such as cyclonic storms and severe cyclonic storms (Fig. 2). Moreover, the climatic data was calculated year-wise from 2006 to 2020, which was considered an average for each year. In addition, spatial and temporal analysis was accomplished using the choropleth method using ArcGIS 10.6 software. Spatial representations into four categories based on numerical values on the chronological order using the natural breaking tool in ArcGIS 10.6 were created; the units of measurement of the climatic data includes rainfall (mm), temperature (°C) and humidity (%). The study reveals the impacts of climate

State-wise paths of cyclones
There were 61 cyclonic disturbances across the Indian coastline during 2006-2020. The maximum number of cyclonic disturbances occurred in Odisha (20), and the second highest cyclonic turbulences traversed West Bengal (14) followed by Andhra Pradesh (11) and Tamil Nadu (11) during 2006-2020. The maximum cyclonic disturbances were crossed at Gujarat (2) and Goa (3). However, Karnataka, Kerala and Maharashtra coastlines had no cyclones during 2006-2020 (Fig. 2). The identification and tracking of cyclonic turbulences assist in facilitation of the necessary precautions and warnings for vulnerable coastal communities. The study considered the starting location of each cyclone which are the Bay of Bengal, Arabian Sea, Indian Ocean and Inland. The results show the state-wise cyclonic paths for the selected study period.
State-wise cyclonic data consists of the data/m/year (which is shown in Table 3) contains the data of the depression, cyclonic storm and severe cyclonic storm. Furthermore, the Southwest monsoon played a major role in producing 29 cyclonic disturbances near the coastal region and 27 cyclonic turbulences associated with the Northeast monsoon, whereas 5 cyclones occurred during the non-monsoon season. Consequently, the study has evaluated three cyclones seasons, i.e. Southwest monsoon (June to September), Northeast monsoon (October to December) and nonmonsoon season (January to May), and these were assessed for climate change appraisal.

Eastern coastal India
Andhra Pradesh Andhra Pradesh is one of the Indian coastal states located in the south-eastern India, where cyclones frequently pass during the monsoon season every year. Consequently, the study has identified that most of the cyclones cross the state during the Northeast monsoon. Andhra Pradesh is a vulnerable coastal zone, experiencing 11 cyclonic turbulences (Fig. 3)   West Bengal The coastline of West Bengal consists of two coastal districts, i.e. Midnapur and South Parganas district, and it encompasses the Sundarbans mangrove ecosystem (Zhang et al. 2021). Fourteen cyclones traversed through West Bengal (Fig. 3); 9 cyclonic disturbances provided the lowest impacts on coastal districts, and 3 cyclonic turbulences created the largest impacts. In addition, 2 cyclonic storms traversed through West Bengal, and 3 severe cyclonic storms crossed, which created a high impact on humans and the environment as these cyclones lead to torrential rain. The resulted in a total of 138 fatalities and displacement of 8,38,000 people in the state (Ehrnsten et al. 2019;Serpetti et al. 2017). These cyclonic turbulences had major impacts on Kolkata and several districts, Sabang, North and South 24 Parganas, East and West Midnapore, Bankura, Howrah, Burdwan, Hoogly, Odisha Based on the appraisal of historical cyclonic data, Odisha state was defined as a highly cyclone-prone area. In total, 20 cyclones crossed throughout the period 2006-2020: 17 cyclonic depressions (Fig. 3) formed on the Bay of Bengal, which resulted in heavy rainfall to the entire coastal district; 1 cyclonic storm came across the Odisha coastline; and 2 severe cyclonic storms (SCS) occurred during the Northeast monsoon. These cyclonic turbulences directly impacted the Balasore, Kendrapara, Jagatsinghpur, Bhadrak, Ganjam, Puri and Khordha districts leading to water-based disasters (floods), with 2007 and 2014 chronicling extreme floods in Odisha. The districts Balasore, Bhadrak, Jagatsinghpur, Jaipur, Keonjhar, and Mayurbhanj, Balikuda and Naugaon experienced 94 deaths, and 90,000 people were displaced during the study period. It is noteworthy that tropical monsoons impacted on one-third of the entire state.
Tamil Nadu Tamil Nadu comprises 14 coastal districts, i.e. Chennai, Kancheepuram, Thiruvallur, Villupuram, Cuddalore, Mayiladuthurai, Nagapattinam, Thiruvarur, Thanjavur, Pudukkottai, Ramanathapuram, Thoothukudi, Thirunelveli and Kanyakumari (organised from north to south), and is one of the most prone to cyclones. According to the Indian Meteorological Department (IMD), 11 cyclones were caused by the northeast monsoon and 5 depressions traversed Tamil Nadu (Fig. 3). The state was predominantly affected by severe cyclonic storms during the northeast monsoon; these were accompanied by various losses such as human life, environment and habitats. Furthermore, two major floods occurred in 2014 and 2015, caused by a tropical cyclone crossing the east coast of India; and low-pressure systems caused flooding in Tamil Nadu. These resulted in the loss of 360 human lives in the Chennai and Cuddalore districts.

Western coastal India
Kerala, Karnataka and Maharashtra The Kerala, Karnataka and Maharashtra coastal states are located in the west India coastal area, lying vertically from north to south sharing boundaries with the Arabian Sea. No cyclones hit during 2006-2020; the Southwest monsoon generated continuous rainfall for the period of June to September causing heavy rainfall and floods near the coastal districts. In 2010 monsoon rain caused floods and landslides in both southern parts (Kerala and Assam) where 50 people were killed and approximately 500,000 people were relocated (ReliefWeb  D 12.08.2006D 29.10.2006CS 25.11.2008CS 23.06.2009D 09.11.2009CS 02.08.2006D 03.09.2006D 21.06.2007D 04.11.2010D 11.06.2011D 01.06.2020SCS 16.08.2006D 23.05.2009SCS 13.11.2008D 25.12.2011SCS 22.06.2015D --12.08.2006D 05.09.2009D 17.05.2010SCS 28.10.2012CS -----28.06.2007D 07.10.2010D 07.12.2010D 13.11.2013D ----05.08.2007D 16.06.2011D 19.11.2013

Goa and Gujarat
The state of Goa is divided into north and south administrative districts. Goa suffered 2 cyclonic disturbances (Fig. 3) (Table 4).

Temperature
The study considered climatic parameters such as temperature, rainfall and humidity which was calculated as an average for each year from 2006 to 2020 (Fig. 4) However, whilst the distribution of average temperatures varies throughout the study period, the maximum average temperature overall was found in Tamil Nadu. Tropical cyclones form based upon intensifying temperatures in oceanic regions. This is also related to greenhouse gas (GHG)-induced surface temperature increase. Furthermore, the world meteorological organization (WMO) global level appraisal (Knutson et al., 2020) concluded that tropical cyclones are extremely unusual compared with other natural causes.

Rainfall
The appraisal of average rainfall in Indian coastal states dates from 2006 to 2020 (Fig. 5), and the study describes the maximum and minimum rainfall for each state. West Bengal's maximum average rainfall observed 2080 mm in the year

Humidity
The humidity is recorded during the study period as a statewide quantity representing the amount of water vapour in the atmosphere as an average distribution. The highest average humidity was measured in West Bengal at 75.04% in 2020 (Fig. 6), and their lowest humidity was measured  In the overall assessment of temperatures, rainfall and humidity, the study identified that the temperature increased in Kerala (0.78 °C) and Tamil Nadu (0.71 °C), whereas in Karnataka (− 0.64 °C) and West Bengal (− 0.60 °C) the temperature decreased. Karnataka (1072 mm) and Goa (605 mm) states received the highest rainfall. Kerala (− 556 mm) and Tamil Nadu (− 285 mm) states rainfall decreased from 2006 to 2020. West Bengal's (4.7%) and Gujarat's (2.8%) humidity increased; Tamil Nadu (− 2.0%) and Karnataka (− 1.6%) observed decreased humidity from 2006 to 2020. Therefore, the overall appraisal noted that the highest changes were documented in Karnataka and Kerala, and the results indicate these states are acquiring rapid climatic changes, with the rest of the coastal states experiencing no change, based on the appraisal of climatic data.

Overall trends of climate change and cyclones in Indian coastal states
Climate change and fluctuations in the climate are the major challenges for sustainable coastal zone management across India and also barriers to achieving the UN SDG 13. This study evaluated the climatic data for the past 15 years, identifying the impacts of climate change on coastal states and revealing that the climate is changing for most of the coastal states with Karnataka, Goa, Kerala, Tamil Nadu, West Bengal and Andhra Pradesh experiencing increasing or decreasing temperatures, abnormal rainfall and humid conditions. As a result of these climate changes, increasing sea level rises (1.7 mm/year) is contributing to other challenges including habitat loss, degradation of coastlines and coastal ecosystems and shoreline changes. Furthermore, climate change is exacerbating coastal erosion within this short time period, leading to coastal area flooding and seawater intrusion. West Bengal suffered the largest proportion of erosion between 1989 and 2001, with alteration along 70% of its coast, followed by Kerala (65%), Gujarat (60%) and Odisha (50%). Sea-level rise and floods may cause greater evacuation in major coastal cities, in addition to the displacement of people along the eastern coast (Dhara 2019). These aforementioned issues are impacting on the Indian coastal states. Cyclones are a natural disaster that strike India almost every year, claiming many lives and wreaking havoc on property. Based upon historic cyclonic data from 2006 to 2020, the study reveals that Tamil Nadu, Andhra Pradesh, Odisha and West Bengal states are severely affected by cyclones during the northeast monsoon. The state of Gujarat is highly vulnerable to tropical cyclones every year by the southwest monsoon. In recent years, cyclonic intensity has been very high and damaged the human and coastal environment.
The direct impact of climate change to the coastal area is also from heavy rains, unbearably high temperatures, humidity, etc. (Chapman et al. 2020;Zhang et al. 2021). These studies have demonstrated the vulnerability of the coastal area and reveal the impacts of climate change on coastal states (Serpetti et al. 2017). A large number of drivers, such as cyclones and floods, are closely associated with climate change (Ehrnsten et al. 2019). This study has been undertaken in coastal states affected by climatic factors such as cyclone, temperature, rainfall and humidity. The study shows the influence of climate change to the coastal states of India. In addition, this should identify the natural hazards determined by climate change and associated human stress in these coastal states. Adaptation to climate change must be implemented for resilience to future disasters as well as to achieve UN-SDG 13.

The study limitations
This study focused on the appraisal of climate change in Indian coastal states where the climatic data was available from 2006 to 2020. Consequently, the analysis is limited to the study duration, and it is not focused on the wider trends of climate change and water-based disasters such as flood and landslide. Furthermore, due to time constraints, the study did not evaluate the impacts of climate change on human health. While the researchers took this into consideration during the conception of the present study, it was not possible to achieve that goal on time.

Conclusions
Climate change (temperature, rainfall and humidity) and cyclones are some of the world's most destructive issues and often lead to destruction in South Asia, particularly India. The regular occurrence of cyclones is widespread in the Indian coastal states and causes significant damage resulting from the effect of storm surges and high tides. To improve information regarding these issues, the current study has assessed the climate change and cyclone trends in nine coastal states of India from 2006 to 2020 by using GIS tools, NASA and the IMD E-atlas and Indian Meteorological Data. The study identified that there has been a rise in highintensity cyclones during the study period. Odisha and West Bengal are the most cyclone-prone states, and Maharashtra, Kerala and Karnataka are the least prone states, though Kerala and Karnataka states recorded the highest average rainfall and highest humidity. The highest average temperature was recorded in Tamil Nadu and Gujarat, and the lowest temperature was recorded in West Bengal and Odisha, although these two states have the highest cyclone vulnerability. These trends once again raise the urgency of further investigations on the relationship between climate change and cyclone activities. The GIS maps, generated from the study results, help to identify the intensity of climate change and cyclones state-wise. The study results also help policy and decision-makers to progress and improve effective strategies for sustainable coastal management. Also, these results help towards achieving one of the goals of the UN-SDG 13 (climate change), which further helps to improve the sustainability of coastal management in Indian coastal regions and also people's lives.