Thank you Mauricio and Pamela (former graduate students, now in their respective faculty jobs at the Universidad de Los Andes, Colombia, and The University of Illinois at Urbana-Champaign) and our partners in India, for this work. Here, we show that the interannual variability of urban malaria in two cities of India is largely driven by variation in relative humidity. A transmission model that incorporates humidity not only explains but also predicts, the size of seasonal epidemics. Urban malaria refers here to falciparum malaria transmitted by a truly urban mosquito vector that exists in South Asia and thrives in the built-in environment of cities. To some extent it is reasonable to expect that humidity should matter; however, much population modeling of mosquito-borne infections has been focusing on temperature and getting deeper into the way this climate parameter acts on both vectors and pathogens within vectors. We argue that we also need to pay attention to humidity (and not as a simple “substitute” for rainfall); it is surprising to see how well a transmission model with this variable accounts for the year-to-year variation in reported cases.