In some of the most agriculturally rich regions in the U.S., researchers from San Diego State University are working to understand how climate change is impacting heat in rural areas and the farmworkers who toil in them.

They’re putting sensors on workers to measure their heart rates and core body temperatures while they work, and evaluating environmental temperatures to assess occupational heat risk. Rising temperatures, decreased water supplies and shifting crop patterns are changing microclimates and increasing exposure to extreme heat for farmworkers, who are already among the most vulnerable to it.

How farmworkers' heat stress might vary by crop, seasons and the number of breaks they take are things researchers are trying to understand.

Over the past two years, they've collected critical, year-round data from some 300 farmworkers. Body sensors measures things like their core body temperature and heart rate while they work. Elsewhere in the fields, environmental monitors measure the day's temperature, humidity, wind speed, sun angle and cloud cover, also known as the wet-bulb globe temperature, the gold standard for understanding heat stress. Together with satellite imagery, researchers are analyzing and mapping where heat is more extreme, especially in the Imperial Valley. 

Researchers are learning that ground level crops can expose workers to higher heat levels compared to tree crops, for example, but it also depends on their harvesting months. Farmworkers who prepare land in the summers for planting or those who help maintain irrigation systems are also more exposed. 

Bordered by the Colorado River to the east, the Salton Sea to the west and Mexico to the south, the Imperial Valley is home to hundreds of thousands of acres of farmland and produces billions of dollars in agricultural production. It grows two-thirds of winter vegetables consumed nationally and provides jobs for thousands.

From 2023 to 2024 alone, about 17,579 migrant and seasonal farmworkers were employed in Imperial County, according to the state. 

It's also extremely hot. In a given year, there are about 123 days with temperatures over 95 F (35 C), and the mercury often exceeds 110 F (43 C) in August and early September. The county has one of the largest Latino populations and the highest number of heat-related illnesses among workers than anywhere else in the state.

Some of their data analysis has already been published. 

One study found that irrigated land in the Imperial Valley reduced the wet-bulb globe temperature on summer days due to evaporative cooling. But on summer nights, the opposite happened: irrigation increased the temperature due to humidity spiking. Irrigation also increased temperatures in urban and fallow areas near crops fields. 

Through this research they were also able to recommend how often farmworkers should be resting to protect them from heat stress based on wet-bulb temperature measurements. While California has heat rules, they're not strictly enforced.

(AP Video by Jae C. Hong, produced by Joshua A. Bickel)

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