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The path of the Loo (orange arrows) from its origins in the deserts of the Indian subcontinent towards and through the Indo-Gangetic Plain of India and Pakistan

 Loo is a strong, hot and dry summer afternoon wind from the west which blows over the western Indo-Gangetic Plain region of North India and Pakistan. It is especially strong in the months of May and June. Due to its very high temperatures (45 °C–50 °C or 115°F-120°F), exposure to it may lead to heatstrokes.Due to its extremely low humidity and high temperatures, the Loo also has a severe drying effect on vegetation leading to widespread browning in the areas affected by it during the months of May and June.

Origin 
The Loo mainly originates in the large desert regions of the northwestern Indian subcontinent: the Great Indian Desert, the Cholistan Desert and the desert areas of Southern Balochistan.

 Loo ends in late summer, with the arrival of  monsoon. In some areas of North India and Pakistan, there are brief, but violent, dust storms known as Kali Andhi (or black storms) before the monsoon sets in.

Adaptation to the Loo

Since the plains of North India and Pakistan are both very hot and extremely dry during this season, water evaporates quite readily. Although this leads to the drying out of many ponds and lakes, the extreme dryness of the air is also easily exploited to create evaporation-based cooling systems. Windows shielded with fiber-screens of the fragrant khas (ख़स/خس or vetiver) dry-grass that are kept damp with a simple water-pumping mechanism are quite effective as an inexpensive form of air conditioning, and have been in common use throughout the plain portions of the northern Indian subcontinent for centuries. Because evaporation proceeds at a very rapid rate in the extreme dryness, the cooling effect can be quite dramatic and result in dwellings where the interior feels chilly. The water in the screens evaporates very rapidly, however, so it must constantly be replenished from raised tanks or with pumps (that can sometimes be driven by the Loo itself). Any water reservoir used must also be shielded from the Loo and the sun, or it can rapidly be depleted.

Ecological effects and Benefits

Many birds and animals succumb to the Loo in the summer months, especially in deforested areas where the Loo blows unhindered and shelter is unavailable. Certain insect-borne diseases, such as malaria, have historically registered dips during the Loo season as insects populations also plummet during this season. Even prior to the 1897 discovery that mosquitoes transmitted malaria, British officials in India had noticed that the Loo in the plains of Northern India naturally made the region relatively free of the disease.

Loo in popular culture

Due to the dangerous, and potentially fatal, effects of the loo on vegetation, humans and animals, it is sometimes referred to as an evil wind in popular Indo-Pakistani culture. Avoiding exposure to the Loo is strongly recommended for children and the elderly, as well as pets. Most people attempt to stay indoors as much as possible during afternoons in the Loo-affected months. Heatstrokes are commonly referred to as Loo lagna (being stricken by the Loo). Certain sherbets, which are popularly believed to have a cooling effect on the body and provide some protection against Loo-caused heatstrokes, are widely consumed during the Loo-season. These include sherbets of rose, khus, shahtoot, bel and phalsa. A specific Unani recipe called Rooh Afza combines several of these popularly believed cooling agents, and is sold commercially as a syrup to flavor sherbets, cold milk drinks, ices and cold desserts, such as the popular falooda. Lassi, a yogurt-based drink of North India and Pakistan, is also extremely popular and believed to confer some protection against the Loo. Sattu, a popular drink in Bihar and Eastern Uttar Pradesh is a drink which gives relief from the scorching heat.Thandai is also used for the same.handai Additionally in the desert state of Rajasthan Keri ka Panna(drink of raw/unripe mango) is a very popular way of remaining cool and resilient to Loo. Panna is also consumed in other parts of the country.

Source:Wikipedia