Call it what you will – poncho, deel or duster – but a rain jacket is essential for protection against hypothermia this spring.

JUST 3.6 DEGREES FAHRENHEIT – that’s all your core body temperature needs to drop before vital organs malfunction and you risk dying of hypothermia. An average of 689 Americans die from hypothermia-related deaths every year. Not surprisingly, Alaska accounts for the most deaths, while New Mexico holds the number two spot, proving that hypothermia isn’t exclusive to cold and wet climates.

Horsemen the world-over have developed innovative solutions for keeping hypothermia at bay in extreme climactic conditions. Their clothing goes by different names, but share one thing in common: an ability to envelope the body in a layer of dry, warm air to moderate body temperature.

Mongolia’s nomadic horsemen are well adept at surviving harsh weather conditions. In fact, Genghis Khan’s generals were notorious for attacking in the dead of winter, when their enemies least expected. Their pinnacle wintertime campaign was in 1237 when 35,000 mounted archers rode up the frozen Volga River to invade Russia. The horsemen were impervious to the cold, thanks to their multi-layered uniforms that included silk underwear, deel robes, chain mail armor, fur-lined boots and quilted hats with earflaps.

The deel has stood the test of time.  Today, it’s a common sight in Mongolia, from the grassland steppes to the capital city of Ulaanbaatar. Wearing a deel feels like you’ve been wrapped inside a Queen-size quilt that is held in place with a silk belt and buttons that fasten like a double-breasted suit. In the bitter cold, Mongols stand with their arms crossed and their hands tucked inside the opposite sleeve, looking like a Jedi Knight from the movie Star Wars – an apt comparison, since George Lucas drew many of his costume designs from Mongolian culture.

Halfway around the world, native Indians in the Andes Mountains of South America devised the poncho. The poncho’s brilliance is its simple design – it is a wool blanket with a slit in the center that you stick your head through. Archeologists aren’t sure how long ago the poncho was invented, but it was widely used by the time Spanish conquistadors arrived in the 16^th century.

The poncho perfectly suited the needs of a horseman, keeping him warm and protected from wind, rain and snow, without hampering the use of his arms and legs while riding (the one drawback of a Mongolian deel is the challenge of riding a horse while rolled inside of a blanket).

The poncho’s influence spread across the continent where variations emerged: the zarape in Mexico, the chamanto in Chile, and the ruana in Venezuala. However, nowhere is the poncho more iconically associated with horsemen than in Argentina, where the cattle-raising gauchos have worn them for over 300 years.

Authentic ponchos are loom-woven, using handspun wool. Depending on how tight the weave, a poncho is impressively watertight. I lived in mine for years, working as a gaucho in the Andes Mountains where the temperatures dropped to zero during the winter, and below freezing in the springtime.

At some point in the mid-1800s, the first truly waterproof poncho was manufactured by coating the fabric in a revolutionary new material called gutta-percha, a latex-like sap from Southeast Asia. Industrialized, latex ponchos spread across Europe and the Americas. In the 1859 book The Prairie Traveler, a guide for American pioneers going west, the author includes “gutta percha poncho” in his packing list, indicating how far the technology of latex ponchos had spread by that year. It would go onto to be widely used by cavalry and infantry soldiers in every conflict since the American Civil War.

Our last stop on the world tour of hypothermia is Abroath, Scotland, where sailors invented oilcloth in 1795. Mariners had waterproofed their sails by soaking them in fish oil for centuries, but Scotland-based Francis Webster Ltd. soaked their sails in linseed oil to create a more pliable, lightweight and less smelly sail fabric.

In the late 1800s, another Scotsman, Edward Le Roy, exported oilcloth technology to New Zealand where he started a sail manufacturing company. Le Roy recognized oilcloth’s potential as a waterproof garment material and designed a long overcoat for sailors. The jacket caught the eye of Australian horsemen who suffered under dusty and rainy conditions.  The only problem for horseman was that linseed oil is flammable and there was a spate of jackets igniting around the campfire.

Australian manufacturer Driza-Bone improved the jacket by using a nonflammable proofing compound and adding design features customized to suit horsemen –a slit fantail to keep a rider and their saddle dry and leg straps to keep the jacket fastened to the body.

The Australian duster entered the American conscious in 1966, as a prominent costume feature in Sergio Leone’s spaghetti Western The Good, the Bad and the Ugly (coincidentally, Clint Eastwood’s character Blondie also popularized the poncho) and more permanently in the 1982 “Australian Western” The Man from Snowy River.

The National Oceanic and Atmospheric Administration (NOAA) is calling a “wild card” weather year in 2012. The past two winters saw back-to-back La Nina effects, an oddity itself, but NOAA predicts a phenomenon called Arctic Oscillation (bursts of cold air from the north, that are hard to predict) will really impact weather in 2012.

“The erratic Arctic Oscillation can generate strong shifts in the climate patterns that could overwhelm or amplify La Niña’s typical impacts,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center.

Whether it’s rain, snow, hail or a leaky Nalgene bottle, water is the one element horsemen the world-over must contend with. Combined with the effects of erratic weather, it doesn’t take long for those precious 3.6 degrees of core body temperature to fall away, creating the risk of hypothermia.

Whatever you choose a poncho, deel or duster to combat the weather this spring, remember: Don’t hit the trail without it.