Timing of rainfall occurrence altered by urban sprawl

The impact of urban changes from 1989 to 2015 on urban rainstorms is assessed for the rapidly expanding Indian city of Hyderabad. A typical event that occurred during 12-14 June 2015 is simulated, and the possible association between altered urban-sprawl and shifts in the rainfall timing and patterns are analyzed. The simulation results revealed that the consideration of urban footprint changes was necessary to correctly simulate the heavy rainfall in the high-resolution Weather Research and Forecasting (WRF) model. With the urban expansion and associated anthropogenic heating (AH), the rainfall was more distributed, and its occurrence delayed by similar to 1-2 h. The results suggest that urbanization can affect rainfall both in terms of the timing as well as the location with respect to the urbanized area. The urban downwind region received an increased rainfall, and this spatial shift was more pronounced with increasing urbanization - from being over the urban area to over rural-urban boundary downwind of the city. The analysis of hydrometeors indicated that rain and cloud quantity decreased with an increasing AH in the urban area. Study results highlight the possibility that the change in the rainfall timing is another climatological signature of urban modification of rainfall.