Heat and humidity exposure in megacities: An applied tool for energy and water harvesting technologies

Concerns about climate change are driving the development of novel technologies for mitigation and adaptation. Some of them include electricity generating and water harvesting based on atmospheric humidity. The latter is already commercial and can generate 50 L of drinking water per day per capita for dozens of people; however, besides energy, operation requires sufficient levels and durations of humidity and temperature. Our study focuses on the 33 megacities of the world, characterising the humidity and heat stress regimes during the last decade, using data from meteorological stations in their vicinity, and ranking them by their exposure and vulnerability to intense heat stress and their suitability to use these moisture-reliant technologies. Our findings indicate the dominance of severe heat stress conditions in megacities located in developing countries. Ranking the megacities according to the intensity and duration of the heat stress shows the annual, monthly and hourly courses. The five most affected are the cities of Chennai, Bangkok, Kolkata, Karachi and New Delhi. Seven megacities suffer continuous, at least 12 h, of intense heat stress during 1–4 months. The ranking also considered the level of income of the countries, hence their vulnerability. On an annual basis, approximately half of the megacities are highly suited for moisture-reliant technologies, among them megacities ranked as the top three in exposure to intense heat stress conditions—Chennai, Bangkok and Kolkata. When focusing on the humid season, 27 out of 33 megacities (82%) obtain suitable conditions for the new technologies and thus can benefit from them, at least part of the year. The implementation of humidity technologies for green energy and clean water could be of great help as our world gets more populated, warmer with higher water demand, especially for populations with insufficient infrastructure and resources.