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

**Rainfall Pattern Analysis over India in Relation to the** 

DOI: 10.5772/intechopen.72870

Shajimon K John Additional information is available at the end of the chapter

Shajimon K John

Additional information is available at the end of the chapter

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

#### **Abstract**

Rainfall over a region across the earth is the prima face reason of its uniqueness. Different regions over the earth having different rainfall pattern in turn is directly related to the regions uniqueness, it is referred as ecosystem. India is one of the ancient regions having different rainfall pattern which has developed into places with its own unique ecosystem prevailing over its different states. Kerala the southernmost tip of this sub-continent has almost clear green top throughout the year in comparison to various other states in the country. This work mainly concentrates on the variation of rainfall over the state of Kerala in comparison with other states which are its neighbours. Rainfall data over the last century is being analysed for finding out whether the rainfall pattern over the state of Kerala has any relation with the rainfall pattern across the country. Solar activity and the number of sun spots and how these activities effect the rainfall pattern also a major area to be investigated.

**Keywords:** rainfall, monsoon, solar activity, Kerala, India

#### **1. Introduction**

Rain is the most beautiful activity in nature which supports the healthy living. Rain is defined as the liquid water in the form of droplets that have condensed from atmospheric water vapour and becomes heavy enough to fall under gravity in every scientific write-up. It is the most significant means of keeping the fresh water level in the earth to its normal level. Rain occurs when the water droplets or moisture are moving across the multi-dimensional temperature moisture profile [1]. We, as human being should be very much indebted to this natural phenomenon. Unfortunately, over the years due to many stated and unstated reasons the rainfall pattern has a change in its pattern as well as the amount of rainfall. Rainfall occurs when moisture contained air rises above the earth's surface and cools to form clouds which in

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© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

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.

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

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

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

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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

September [13, 14].

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