**2. Study area**

The study area is India, in the Asian continent. The study area has much uniqueness with respect to rainfall pattern as well as the climatic characteristics. India is one of the oldest civilizations with a wide cultural heritage. One of the major driving force towards this wide cultural heritage is the difference in climatic characteristics prolongs through the area. The region covers snow covered Himalayas in the north to tropical rain forests in the south. The types of mountains, rivers and sea shores make India a distinct geographical entity in Asia. It is bound by the Himalayas in the north to tapper between Indian Ocean in south, Bay of Bengal in the east and Arabian Sea in the south. The region lies entirely in the northern hemisphere (https:// www.mapsofindia.com/geography/). The mainland extends between latitudes 8° 4′ and 37° 6′ north, longitudes 68° 7′ and 97° 25′ east and measures about 3214 km from north to south between the extreme latitudes and about 2933 km from east to west between the extreme longitudes. The climate of the subcontinent is mainly depending on its altitude, latitude, monsoon winds and tropical cyclones [7, 8]. The presence of Tropic of Cancer through the middle of the region keeps the climate near tropic and sub tropic style. The presence of high altitude Himalayas in the north keeps the winter temperature milder than the rest of the central Asia regions. The monsoon winds flows from the southern tip from Bay of Bengal and Arabian Sea have a significant effect on the rainfall across the country. Most of the regions are also under the effect of cyclones from Bay of Bengal.

The climate within India can be mainly classified into four major categories: tropical dry, tropical wet, sub-tropical humid and mountain climate. The elevated regions in the Himalayas experience snow during the winter season. At the same time Thar Desert experience tropical dry climate. The Himalayas and the Thar Desert influences the climate over the Indian sub-continent a lot. The Himalayas act as a barrier against katabatic winds which blow from Central Asia [8–10]. Overall the country's climate inclined more towards tropical since the Tropic of Cancer passes through the middle of the country. The tropical wet climatic regions within the country can be sub divided into; tropical monsoon climate and savannah climate. The major areas which fall in tropical monsoon region are Lakshadweep, Andaman and Nicobar Islands, southern Assam, the Western Ghats and Malabar Coast. These areas experience moderate to high temperature along with high rainfall during monsoon season; from June to November. The high amount of rain received in these regions keeps these regions green throughout the year [11, 12]. The savannah climate is the most commonly prevailing climate in the country. Almost all inland areas experience the savannah (tropical wet and dry) climate, with extremely high temperature during summer and moderate to heavy rainfall during monsoon which normally occurs during June to September [13, 14].

turn precipitate to fall as rain. This precipitation can reach earth's surface as rain, snow, sleet or hail depends on the pressure variations across the region [2, 3]. Maximum rainfall occurs near the earth's equator because these regions having very high direct sunlight impact with very high temperature which creates high level of vertical uplift or air. The presence of mountains in this region increases the uplift of air. The opposite happens in Polar Regions, where the air is very cold and contains high amount of water level which enable only low level of vertical uplift. This forces the air to descend down preventing from any cloud formation.

Rainfall study is mainly known as climatology which includes process of measuring, understanding, and predicting rainfall pattern across the earth surface [4, 5]. The major factors which have direct impact on the amount of rain received over a region are humidity, air pressure, region's topography and the type of cloud formed over the region. Based on the amount of rain received over a specific period is used an instrument to classify the climatic regions over the earth known as Köppen classification [4–6]. According to Köppen classification, five primary types named as tropical, dry, mild mid latitude, cold mid latitude and polar. These primary classifications are again subdivided into rain forest, having the maximum rainfall, monsoon, tropical savannah, humid sub-tropical, humid continental, oceanic climate, steppe,

The study area is India, in the Asian continent. The study area has much uniqueness with respect to rainfall pattern as well as the climatic characteristics. India is one of the oldest civilizations with a wide cultural heritage. One of the major driving force towards this wide cultural heritage is the difference in climatic characteristics prolongs through the area. The region covers snow covered Himalayas in the north to tropical rain forests in the south. The types of mountains, rivers and sea shores make India a distinct geographical entity in Asia. It is bound by the Himalayas in the north to tapper between Indian Ocean in south, Bay of Bengal in the east and Arabian Sea in the south. The region lies entirely in the northern hemisphere (https:// www.mapsofindia.com/geography/). The mainland extends between latitudes 8° 4′ and 37° 6′ north, longitudes 68° 7′ and 97° 25′ east and measures about 3214 km from north to south between the extreme latitudes and about 2933 km from east to west between the extreme longitudes. The climate of the subcontinent is mainly depending on its altitude, latitude, monsoon winds and tropical cyclones [7, 8]. The presence of Tropic of Cancer through the middle of the region keeps the climate near tropic and sub tropic style. The presence of high altitude Himalayas in the north keeps the winter temperature milder than the rest of the central Asia regions. The monsoon winds flows from the southern tip from Bay of Bengal and Arabian Sea have a significant effect on the rainfall across the country. Most of the regions are also under

The climate within India can be mainly classified into four major categories: tropical dry, tropical wet, sub-tropical humid and mountain climate. The elevated regions in the Himalayas experience snow during the winter season. At the same time Thar Desert experience tropical dry climate. The Himalayas and the Thar Desert influences the climate over the Indian sub-continent a

subarctic climate, tundra, polar ice cap and desert [4, 5].

the effect of cyclones from Bay of Bengal.

**2. Study area**

18 Engineering and Mathematical Topics in Rainfall

The tropical dry climate is again sub divided into three mainly; sub-tropical arid (steppe) climate, tropical semi-arid (steppe) climate, and sub-tropical arid (desert) climate. Regions around Karnataka, Central Maharashtra, Andra Pradesh and some parts of Tamil Nadu experiences Tropical semi-arid climate experience with hot and dry summers during March to May and almost very unreliable and erratic rainfall. Western Rajasthan regions of Thar Desert fall into the sub-tropical arid (desert) climatic region. The region where the desert extends like parts of Punjab, and Haryana comes under sub-tropical semi-arid climate regions. These regions experience high temperature during summer and rain normally occurs during summer monsoon only. Sub-tropical humid climate experienced in most of the North and Northeast regions. In these regions summers are hot to very hot while during winter season the temperature may dip to 0°C [15, 16]. These regions also experience rainfall during summer with sporadic rain or snowfall during winter. The summer occurs during May to July while the winter occurs during December and January. The mountain climate mainly happens in the Himalayas region with an average temperature fall of almost 0.5°C with every 100 meters rise in height.

The effect of these different climatic styles on the country is that it has mainly four different seasons; winter, summer, rainy season and autumn. The months of December, January and February are generally considered as winter months in most of the north and north eastern regions. The average temperature may vary around 10° to 15°C in the northern region while the southern regions has an average temperature between 20° to 23° centigrade [17, 18]. Some parts like western Himalayas and Kerala experiences rain during this season also. The pre monsoon season or summer or hot weather conditions occur during March to June with an average temperature rises up 35° centigrade. The central and northern and north western regions near to Thar Desert the temperature may reach up to 45° to 48°C. While the coastal areas record moderate temperature due to the influence of sea breeze. Some parts of north eastern and eastern areas witness thunderstorms also during these months. The areas near to Thar Desert witness hot and dry winds along with sand/dust storms. Around 75% of the total rain received across the country falls during the South West monsoon [19, 20]. The start of South West monsoon happens during last week of May or the first week of June and this season extends up to September. The extent of this season varies from region to region as the southern state of Kerala almost four to four and half months under this season while the western state of Rajasthan having less than two months. The monsoon arrives in the Indian

**Figure 1.** The climatic regions over Indian subcontinent. (courtesy: Maps of India, https://www.mapsofindia.com/maps/ india/climaticregions.htm).

of the country depend mainly on this South West monsoon. There are many stated reasons which have direct impact on the monsoon like; sea surface temperature, snow cover and El

**Figure 2.** Physical map of Kerala (courtesy: Maps of India, https://www.mapsofindia.com/maps/kerala/keralaphysical.

Rainfall Pattern Analysis over India in Relation to the State of Kerala

http://dx.doi.org/10.5772/intechopen.72870

21

The post monsoon season or the Northeast monsoon occurs for nearly two months, October and November across the country. This season is mainly treated as the retreating of rainy season the country [21, 22]. Most of the Southern states of the country like Kerala, Tamil Nadu and Karnataka receive almost 30% of their annual rainfall during these months. This period also experiences decrease in temperate from an average around 35–28°C. Another highlight during this season is that the humidity level decreases across the country with clear to very clear sky throughout the day [23, 24]. **Figure 1** shows how various climatic regions discussed above are mapped across the Indian subcontinent. Depending upon the latitude and longitude of the region along with its proximity to the Bay of Bengal or Arabian Sea and the presence of

mountainous regions determines the regions climatic style.

Nino [20].

htm).

subcontinent through Bay of Bengal and Arabian Sea. The effect of monsoon through Arabian Sea is almost three times stronger than the effect of Bay of Bengal with the monsoon through Arabian Sea extends its presence into the Thar Desert region. The greenery and the agriculture

**Figure 2.** Physical map of Kerala (courtesy: Maps of India, https://www.mapsofindia.com/maps/kerala/keralaphysical. htm).

of the country depend mainly on this South West monsoon. There are many stated reasons which have direct impact on the monsoon like; sea surface temperature, snow cover and El Nino [20].

The post monsoon season or the Northeast monsoon occurs for nearly two months, October and November across the country. This season is mainly treated as the retreating of rainy season the country [21, 22]. Most of the Southern states of the country like Kerala, Tamil Nadu and Karnataka receive almost 30% of their annual rainfall during these months. This period also experiences decrease in temperate from an average around 35–28°C. Another highlight during this season is that the humidity level decreases across the country with clear to very clear sky throughout the day [23, 24]. **Figure 1** shows how various climatic regions discussed above are mapped across the Indian subcontinent. Depending upon the latitude and longitude of the region along with its proximity to the Bay of Bengal or Arabian Sea and the presence of mountainous regions determines the regions climatic style.

**Figure 1.** The climatic regions over Indian subcontinent. (courtesy: Maps of India, https://www.mapsofindia.com/maps/

subcontinent through Bay of Bengal and Arabian Sea. The effect of monsoon through Arabian Sea is almost three times stronger than the effect of Bay of Bengal with the monsoon through Arabian Sea extends its presence into the Thar Desert region. The greenery and the agriculture

india/climaticregions.htm).

20 Engineering and Mathematical Topics in Rainfall

Kerala even with its closeness to equator when compared to other states in the country, has a composed and pleasing climate with temperature lies between 28–35°C throughout the year. The presence of sea in its west side and Western Ghats in the west side are the major reason for this pleasing climate. Kerala lies between north latitudes 8°.17′.30" N and 12°. 47′.40" N and east longitudes 74°.27′47″ E and 77°.37′.12″ E. The climate is mainly tropical wet due the presence heavy monsoon which starts from June and extends till September (https://www.mapsofindia.com/maps/kerala/geography-and-history/). **Figure 2** shows the physical map of Kerala.

Kerala can be divided into three climatically distant regions namely, hot and wet coastal areas along the west, central midlands and eastern highlands. The region lies in the centre of Indian tectonic plate with gradual increase in altitude from coastal areas to western highlands. Kerala experiences mainly three seasons; south west Monsoon, north east Monsoon and summer [25, 26]. The south west monsoon is the most prominent source of rainfall across the region with almost 65% of the total rain received during this season. The southwest monsoon, which is known as "Edavapathi" in the colloquial language, means mid of Malayalam month Edavam, start during the end of May or first of June with support of southwest monsoon wind [27–29]. Across the state 42 rivers flow from Eastern Ghats to the Arabian Sea which are fed by these rains. Northeast monsoon, known as "Thualavarsham", occurs during the retarding of southwest monsoon. This occurs during October and November. The main characteristics of this rainy season are the prudential rains with lighting and thunder. Summer starts towards the start of March with reaching higher temperature around 40°C at certain places [30–33].
