Unity and Diversity in the Monsoon Climate

The monsoon is the great unifier of India’s climate, linking the subcontinent with the rest of Southeast Asia in a single weather rhythm. But that unity is only half the story. Within this one climatic regime, India hides astonishing diversity — so much so that the climate of Kerala and Tamil Nadu in the south is worlds apart from that of Uttar Pradesh and Bihar in the north, even though all of them share the monsoon type of climate. These regional variations show up in the pattern of winds, temperature and rainfall, in the rhythm of seasons, and in the degree of wetness or dryness. Together, they form what may be described as sub-types of the monsoon climate.

Regional Variations in Temperature

The temperature contrasts across India are extreme, and they play out both seasonally and regionally.

• In summer, the mercury occasionally touches 55 °C in western Rajasthan, while in winter it drops to as low as minus 45 °C around Leh.
• On a single June day, Churu in Rajasthan may record 50 °C or more, while Tawang in Arunachal Pradesh barely touches 19 °C on the same day.
• On a December night, Drass in Ladakh may fall to minus 45 °C, while Thiruvananthapuram or Chennai on the same night records 20 °C or 22 °C.

These examples confirm that seasonal variations in temperature exist from place to place and from region to region. But the variation is no less striking even if you take a single place and record its temperature for just one day. In Kerala and the Andaman Islands, the difference between day and night temperatures is hardly seven or eight degrees Celsius. In the Thar desert, however, if the day temperature is around 50 °C, it may drop down considerably at night — up to 15–20 °C.

Regional Variations in Precipitation

The diversity in rainfall is just as dramatic, and it shows up in the type, amount and timing of precipitation.

• While snowfall occurs in the Himalayas, it only rains over the rest of the country.
• Cherrapunji and Mawsynram in the Khasi Hills of Meghalaya receive over 1,080 cm of rainfall in a year, while Jaisalmer in Rajasthan rarely gets more than 9 cm in the same period.
• Tura in the Garo Hills of Meghalaya may receive in a single day an amount of rainfall equal to ten years of rainfall at Jaisalmer.
• Annual precipitation is less than 10 cm in the north-west Himalayas and the western deserts, but it exceeds 400 cm in Meghalaya. …