Sensitivity study on storm modulation through a strategic use of consumer air conditioners

Storm trainings, consisting of quasi-stationary band-shaped precipitation systems, bring persistent local heavy rains, often causing devastating floods and landslides. Here, we show that a strategic use of consumer air conditioners can modulate a storm downstream. We numerically reproduced a storm training that damaged the Hiroshima metropolis in Japan in 2014, and conducted experiments to test the sensitivity of the storm to the initial moisture field near the surface. We propose an empirically-derived formula for a control efficiency parameter, which can be used to estimate the impact of moisture removal on the rainfall accumulation. That formula can be different for different storms and used to assess the feasibility of modulating the target storm. It reveals that removal of half a kiloton of moisture, which could be achieved within half an hour in a city with a population of 1 million since more than one air conditioner is installed per capita in Japan, could lead to a significant reduction of the total rainfall accumulation over a 100-km² area of heavy rain during the Hiroshima storm event. We anticipate our results, which reveal that human activity can have a significant impact on storms, will be a starting point for considering the coupling of weather and the economy, and will contribute to the development of a sustainable society.