Distribution of Rainfall

Rainfall is one of the key aspects that determine several factors. The agricultural sector primarily depends on agriculture. Without even rainfall every year, the agricultural sector would go for a toss. With the agricultural sector being affected, the manufacturing sector will immediately be affected too, and subsequently, the service sector will also be affected. Rainfall is hence, not just necessary for the environment but also rain distribution plays a deterministic role in shaping up the economy of a region. To prove this, take into consideration the hot equatorial countries of Africa. These countries have deserts stretching up to miles and miles. These countries generally are poor, this is mainly because of the lack of rainfall. Since there is no even distribution of precipitation, these countries fail to even grow crops for consumption. Due to the lack of vegetation, all the industries are considerably hurt and ultimately the economy of the country is stunted. Today let us understand more about the global types and distribution of precipitation and the different types and distribution of precipitation. 

Distribution of Rainfall in India

Before we move on and understand the world distribution of rainfall, let us take a look at the distribution of precipitation in our country.

Bimodal Distribution of Rainfall in India

India is a very vast country and has a huge landmass. The country covers about 30 time zones, which explains the vastness of the country's dimensions. Due to such a huge size, the terrain in every region differs from one another. Now, let us understand more about the temporal distribution of rainfall in India. 

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Well, the generalization of annual rainfall in India would not be apt. This is because the region in India that receives the highest rainfall and the region that receives the lowest rainfall is approximately 1178 cms. That's how diverse our country is. The distribution of precipitation in India is not spread across the year evenly and is irregularly spread throughout the year. The monsoon season in our country starts from the month of June and lasts till almost late September. The southeastern parts of India even receive adequate retreating monsoon in the month of November and December. If we look at this scientifically, any region in the world can be classified as

• Subtropical arid desert

• Tropical semi-arid

• Sub-tropical semi-arid

• Subtropical humid

• Tropical rainforest

• Alpine

• Tropical Savannah

According to the metrological department of India, the average rainfall seen by India in a year is around 118 cm. Now let us classify different regions of India into categories based on the distribution of rainfall in a year. 

• Regions of extreme precipitation

India is a diverse country, from the deserts in the northwestern region to the rainforests in the northeastern states, rainfall is scattered unevenly. The northeastern states of India are mainly comprised of rainforests and experience very high annual rainfall. The regions of India with extremely high rainfall include the northeastern states of Assam, Meghalaya, Arunachal Pradesh, a few parts of the western ghats (mainly the windward side). In these regions, the rainfall is extremely high, and hence dense evergreen tropical forests flourish. The average rainfall received by these regions is approximately 400 cms. The village that receives the highest annual rainfall is Mawsynram village in Meghalaya. Fascinatingly, the village experiences an extended period of monsoon. The village sees dark clouds and rain for approximately 8 months of the year. During the peak of the monsoon season, the rainfall is almost continuous and it keeps pouring all day and night.

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• Regions of heavy precipitation

Those areas of land where the rainfall experienced are between 200 and 300 cms are all classified as the regions of heavy precipitation. The rainfall experienced here is way above average and in fact pretty high for even facilitating the growth of evergreen forests. The regions of heavy precipitation are also often hilly regions. Plain lands do not fall in this region. The states that lie in this zone are mostly the northeastern states and other hilly regions. These states include Manipur, West Bengal, Tripura, Nagaland, Orissa, Bihar. The sub-Himalayan regions i.e. the lower peaks of the Himalayas are also included in this zone. Therefore, parts of states like Uttarakhand, Himachal Pradesh, Jammu, and Kashmir also would classify in this category of distribution of rainfall. 

• Regions of moderate precipitation

Moderate precipitation regions cover the most number of regions of India. The regions that receive around 100-200 cms of rainfall are the ones that lie in this category. This amount of rainfall is just perfect for hosting a wet deciduous forest. Most regions of India receive this much amount of rainfall in India and hence a majority of the states would be categorized as moderate precipitation regions. The states that come under this category include a few parts of Bihar, Odisha, West Bengal, Madhya Pradesh, Maharashtra, Punjab, Andhra Pradesh, and the leeward side of the Western Ghats. 

• Scanty rainfall distribution regions

These regions are comparatively drier in comparison to the regions of moderate precipitation. This is mainly because the rainfall received here is between 50 and 100 centimeters. The rainfall in these regions is often uneven and scarce. As a result, these regions tend to be drought-prone. Sometimes, these regions receive dangerously low, during a year of low rainfall, the agriculturists in these areas go through several problems. This is because, if the annual rainfall received in a year is too low, the crops would fail. Drought problems are hence a matter of concern in these places. The states that come under this category are parts of Gujarat, Karnataka, Maharashtra, Tamil Nadu, Madhya Pradesh, Andhra Pradesh, Punjab, Haryana, and Western Uttar Pradesh. The common type of vegetation found in these regions is Savannah dry deciduous forests and grasslands. 

• Arid deserts and semi-arid regions 

As we all know, deserts are sandy regions that experience extremely low rainfall and sparse vegetation. These regions generally receive annual rainfall below 50 centimeters. There is almost no means of growing crops in these regions via natural methods. The only vegetation found in these regions is the desert plants such as the cactus. The regions that house Arid deserts are parts of Rajasthan and Gujarat. Both these are hot deserts or tropical deserts. On the other hand, parts of Jammu and Kashmir and Leh and Ladakh also are deserts, however, they classify as cold deserts. Such deserts are not sandy but frozen all throughout the year. The location that experiences the lowest rainfall in a year is the Rumli village, Rajasthan.

What is bimodal rainfall?

What we just took a look at is the temporal distribution of rainfall. However, a few parts of India also experience bimodal rainfall. The retreating monsoon is a phenomenon that causes the seasonal distribution of precipitation. This occurs when the wind direction reversal happens during the winter season. The cold winds from the Antarctic territory flow towards the north. When it reaches the Indian peninsula, the wind is originally dry, however, due to the curved structure of our country, the winds pick up moisture when they flow over the Bay of Bengal. These moisture-laden winds now hit the coast of Tamil Nadu and Andhra Pradesh. Upon hitting the Eastern ghats, dark clouds are formed and precipitation occurs in these states during November and December. This is called the phenomenon of retreating monsoon and causes bimodal rainfall.