Heat Islands in a Sea of Water Conservation: Heat Costs of Turf Replacement Programs

Homeowners face a water versus heat tradeoff when it comes to replacing thirsty grass lawns with water-conserving landscaping, a process touted by water agencies in the U.S. West as a top way to conserve water. Using nearly 200,000 rebate records and remotely-sensed temperature data from Southern California and Southern Nevada, I assess the effect of water-conserving lawn replacement programs on local temperatures and estimate the associated costs of increased heat. Conversions increase summertime parcel temperatures by 0.6°C (1.1°F) on average with substantial heterogeneity throughout the temperature spectrum. Heat effects are twice as large on the hottest 20% of days and for homes with the most removed vegetation. Back-of-the-envelope calculations suggest that the annual costs from increased heat may be up to $1,675 per household, comprised of increased electricity usage ($48) and mortality risk ($306), as well as harder-to-quantify comfort values, diminished cognition, and costly adaptation behavior. These costs exceed the maximum expected water savings for a typical home in Southern California ($954) and Las Vegas ($574), where municipal water is cheaper. This suggests that such rebate programs may not be welfare-improving.