Weighing 'Wind Distribution Pattern' for Building Design in Dhaka City

How Wind Speed and Wind Flow Direction May Influence Shading of the South and Southeast

I wish Dhaka City were windier! (Photo by Keenan Constance on Unsplash)

Neither Chicago nor Seoul, Dhaka rarely experiences the strong breezes typical of such windy cities. However, superimposing wind data on a windrose diagram shows that the Southern and Eastern fronts are not entirely calm. At least 68% of the annual breezes come from the South, East, and Southeast (see Fig. 1 below). In the diagram, the yellow-shaded area represents the combined percentage of wind flow in Dhaka City. Strategically placing openings on the South and Southeast sides would enhance natural ventilation in buildings. Nevertheless, due to Dhaka’s equatorial location, shading design is essential to modulate solar gains during the summer months.

Fig. 1: Windrose of Dhaka City showing the percentage of wind occurrences by flow direction.

The second figure is particularly interesting. Wind speeds of 0–10 km/h (up to 2.78 m/s) occurred about 50% of the time annually (see Fig. 2), which is considered “refreshing” in urban settings at 2–3 m/s. Additionally, wind speeds of 10–15 km/h (2.8–4.17 m/s) occurred nearly 35% of the year. The wind measurement point was 30 feet above ground level. Further analysis revealed that 5 m/s wind speed occurred around 43% of the time in a typical meteorological year, while 1 m/s and 12 m/s were observed 26% and 22% of the year, respectively.

According to the Beaufort wind scale, 1 m/s is classified as light air, barely perceptible outdoors. At 5 m/s, hair is blown, and dust and loose paper are raised. A wind speed of 12 m/s is considered a strong breeze, making it difficult to hold umbrellas. Learn more about wind speed and the Beaufort scale by here. 

Fig. 2: Windrose of Dhaka City showing wind speeds as a percentage of annual occurrences.

April and July are the windiest months. As shown in the following two figures, the period between 10 AM and 7 PM experiences the highest wind speeds during the day. Nighttime winds are generally calmer, with lower air velocities and only occasional gale-force gusts. Wind speeds exceeding 19 m/s are not uncommon, occurring more than 7% of the time in a typical meteorological year.

Fig. 3: Wind speed distribution in Dhaka City, as shown in the two plots above.

Since air movement during the summer months is a key factor in achieving effective natural ventilation, the predominance of winds from the South and Southeast should guide designers’ thinking. I will share more studies on Dhaka City’s wind patterns in future posts. If you have insights or analyses on wind patterns to share, please leave a comment below.

This study was conducted in late 2016 and early 2017 using Autodesk Ecotect Analysis 2011 and Microsoft Excel 2016. Meteorological data for 2000–2009 were provided by Prof. Dr. Monjur Mourshed of Cardiff University, UK. Additionally, weather data from www.meteoblue.com supported this study.