I have addressed regional variations by loosely dividing the country into north, north east, south, west and east, although no such division can cover the entirety of Indian cooking, as that may take a lifetime of travel, research and experimentation !
This diversity can be better understood by exploring four aspects.
Climate⇒ In the hotter regions of India such as in the south, which is close to the Equator, or in Rajasthan, part of which is desert, foods need to be cooling. within the repertoire of spices, chillies are considered cooling as the capsaicin in them makes you sweat. This cools the body down, and therefore foods from these regions are very hot and spicy, unlike in the north, which can be cold and therefore uses a lot of garam masala, a warming spice blend.
Geography⇒ Local foods are at the heart of regional cooking. People living along India’s 4000 mile coastline eat seafood combined with foods such as coconut, which commonly grow there. A Goan fish curry most often has pomfret, a sea fish, gently simmered in tangy, spicy coconut curry. In the fiery heat of the Rajasthan desert, water is scare an food are therefore often cooked in milk.
Religion⇒ Almost 35 per cent of Indians are vegetarian, mainly for religious reasons. Hindus do not generally eat beef and Muslims population does not eat pork. In an Indian home, non vegetarian meals are served only a couple of times a week and these usually include chicken, fish or mutton, which in India is goat meat and not lamb. When Indian dishes are adapted for the Western world, lamb replaces goat. The cost of these non vegetarian foods and the tropical heat mean that family meals are usually lighter and lean towards vegetarian dishes. Vegetarianism in India has its roots in two religions -Jainism and Buddhism- although many Buddhists in India do eat meat. Their religion allows them to eat whatever is offered to them as long as they have not witnessed the slaughter of the animal. The Jain follow non violence further by not even consuming root vegetables such as onion and garlic that may lead to the destruction of life during harvesting.
Foreign influences⇒ These have had large part to play in shaping the modern cuisine of India. The Greeks, Chinese, Mughals, Portuguese, Dutch, French an the British brought their own cuisine, ingredients and coking techniques to India and took delicious spicy recepies alongside spices when they returned home. Today black pepper is used to flavor not just Indian food but many cuisines all over the World. Many ingredients that Indian cooking is based on- chillies, tomatoes,and potatoes- were introduced to India by the Portuguese only about 500 years ago.
According to T.R. Gopalakrishnan,s book “Vegetable crops”, the British introduce cauliflowers and cabbage to india in 1822. British varieties were grown in May/June when India enjoys summer and thus these cauliflowers adapted to the hot and humid conditions of their new environment.
From The Indian Cookery Course