Researchers Map Rural Heat Islands to Protect Farmworkers from Climate Dangers

The Human Cost of Harvesting in Extreme Heat

For farmworkers like Raul Cruz, beating the heat means starting work before dawn in jet-black darkness. By the time most office workers are brewing their first coffee, Cruz and his colleagues have already put in hours chopping sugarcane in California’s Imperial Valley, desperately trying to finish before temperatures become unbearable.

“We just have to because we need to beat the heat,” Cruz told researchers, describing the mental stress of watching temperatures creep up dangerously early in the morning. His experience reflects a growing crisis in agricultural regions where climate change is turning productive farmland into potential death traps for the workers who harvest our food.

Scientific Approach to a Deadly Problem

Researchers from San Diego State University are taking an unusually comprehensive approach to understanding this threat. According to their published methodology, they’re collecting year-round data from approximately 300 farmworkers using body sensors that measure core temperature and heart rate during actual work conditions.

Meanwhile, environmental monitors scattered throughout the fields capture what’s known as wet-bulb globe temperature—considered the gold standard for understanding heat stress because it accounts for temperature, humidity, wind speed, sun angle, and cloud cover. The National Weather Service considers this metric crucial for assessing dangerous working conditions.

“Workers could potentially be dying or having some serious issues,” project leader Nicolas Lopez-Galvez, an assistant professor in SDSU’s School of Public Health, acknowledged in research statements. “It’s better to start acting sooner.”

California’s Accelerating Heat Crisis

The urgency behind this research becomes clear when examining the data. Analysis of state and federal records indicates California temperatures have increased almost 3°F since the start of the 20th century, with warming accelerating dramatically in recent years. Southern California appears to be heating up about twice as fast as northern regions.

Imperial County specifically experiences approximately 123 days annually with temperatures exceeding 95°F, frequently hitting 110°F or higher during August and early September. The region employs thousands of seasonal farmworkers—about 17,579 from 2023 to 2024 alone, according to state employment data—while simultaneously recording some of the highest rates of heat-related illnesses among workers in California.

Surprising Findings About Rural Heat Islands

One of the study’s more counterintuitive discoveries involves irrigation practices. While watering crop fields provides cooling relief during summer days thanks to evaporation, it actually increases heat stress at night when humidity spikes. This creates a dangerous scenario where farmworkers cannot properly recover from daytime heat exposure.

“It is a concern because an elevated nighttime temperature restricts the ability of farmworkers to cool down,” explained Sagar Parajuli, a research scientist with SDSU’s geography department and lead author on published findings. “So they can’t recover from the heat stress they could be accumulating from the daytime.”

The research also reveals that heat exposure varies significantly depending on crop type, with ground-level crops generally creating hotter working conditions than tree crops. Empty fields and areas with limited tree cover can become what Lopez-Galvez describes as “heat islands”—pockets of extreme temperatures that pose disproportionate risks to workers.

From Data to Policy Changes

Perhaps most importantly, the research is translating into concrete recommendations. Analysis has enabled researchers to suggest how frequently farmworkers should take rest breaks based on how often wet-bulb globe temperatures exceed safety thresholds across different seasons and work shifts.

This data-driven approach could fill critical gaps in current protections. As Parajuli noted in study discussions, “We realized that farmworkers are not getting enough rest breaks, and also there are no clear policy guidelines in terms of heat-related rest breaks.” While California does have heat rules on the books, enforcement remains inconsistent according to worker advocacy groups.

The research team plans to expand their work into California’s Central Valley and potentially into Yuma, Arizona, recognizing that the agricultural heat crisis extends far beyond any single region. For the thousands of farmworkers who feed the nation while facing increasingly dangerous conditions, these mapping efforts could mean the difference between a paycheck and a medical emergency—or worse.