Picture (above): Kuala Lumpur at night. Credit: Moosa Haleem (Unsplash).

Major floods and rainfall‐related impacts are often caused by short‐duration heavy rainfall events. Although there is evidence of cities modifying rainfall in many urban areas, uncertainties still exist around their role in intense rainfall episodes.

CLEX researchers as part of an international team investigated the impact of the growth of Kuala Lumpur (Malaysia) on intense rainfall using observations and modelling experiments. They found that over the last three decades hourly rainfall events have become more intense over the city than surrounding rural areas.

The modelling experiments supported this finding and help reveal the mechanisms behind the intensification.

The relative warmth of the city with respect to its surroundings contributed to the increase. The city creates a low‐level anomaly of warm and dry air that then rises.

To compensate for this, the moist surrounding air is brought into the urban area and lifted upward. This feeds the air above the city with moisture and sustains a local circulation initiated by the relative warmth of the urban area.

The researchers found the city’s influence on extreme rainfall is located over the urban area itself, as opposed to other studies that have detected a footprint downwind. This is likely due to the typical calm background wind conditions in the tropics.

  • Paper: Li Y, Fowler HJ, Argüeso D, Blenkinsop S, Evans JP, Lenderink G, Yan X, Guerreiro SB, Lewis E, Li X-F. 2020. Strong Intensification of Hourly Rainfall Extremes by Urbanization. Geophysical Research Letters, 47(14): e2020GL088758. https://doi.org/10.1029/2020GL088758.