Rural Heat Islands:  Interdisciplinary mapping, prediction, and mitigation of farmworker heat stress

Farmworkers are highly vulnerable to heat stress. We describe the results of an interdisciplinary approach to mapping, measuring, anticipating and mitigating farmworker heat stress in the Imperial Valley, California. We combine climate modeling, remote sensing, in situ physiological measurements, farmworker-evaluated apps, and farmworker and stakeholder interviews on structural vulnerability to heat. Several heat guidelines (State, Federal) are evaluated for their impact on mandated rest break minutes. Key findings include: a) air temperature, land surface temperature, and wet bulb globe temperature have all increased over a 20 year period, with increased rates of health threshold excedance; b) crops harvested during the daytime in spring and summer, including orchards and grapes, have the greatest heat exposure and high metabolic expenditure; c) labor-intensive activities other than harvesting continue throughout the summer, with consequent risk of heat exposure; d) guidelines that use air temperature result in significantly fewer rest minutes than heat indices such as the wet bulb globe temperature; e) farmworkers are subject to structural vulnerability due to lack of political power and socioeconomic status, resulting in persistent heat exposure with weak government oversight or enforcement; f) web-based apps can be developed and evaluated in collaboration with the farmworker community to provide early warning systems and real-time guidance on adaptive and protective behaviors. We conclude with recommendations for policy, management, interventions, and adaptation measures, including plans to evaluate in-field cooling structures.