In March of 2018, Nairobi was pounded by a series of heavy rainstorms. The city experienced 15.5 centimeters of precipitation, 20% more than expected.¹ 4.9cm of that rain fell on March 6th alone, with a second major storm striking on the 15th and bringing an additional 2.9cm. Major roads were flooded, bringing business in the capital of Kenya to a halt. Bystanders were sharing pictures and videos of vehicles stranded on flooded roads. In this post, we use data from Uber Movement to measure the impact of that rainfall and subsequent flooding on the city’s road network.
The following visualizations compare average weekday travel times in February to travel times during the rainstorms on March 6th and 15th, respectively. Zones are determined by Hex Clusters, a set of geographic boundaries drawn by Uber, for use in statistical and travel analysis. Red areas depict an increase in travel times, while green indicates a decrease in travel times.
As shown in Figure 1, travel times on March 6th from the central business district of Nairobi to regions in the south and east increased significantly, by as much as 124%. Slowdowns are particularly noticeable in zones near rivers, likely due to river flooding of streets which vehicles commonly traverse during commutes.
The Movement data also points to the specific time period when travel times were at their highest. The March 6th rainfall had a noticeable impact on travel times during PM peak and evening periods — the time of day when commuters would be making their way home in compromised lighting.
On March 15th, travel times were particularly long in the middle of the day (Fig 3). Rains and flooding had a similarly dramatic impact on travel times throughout Nairobi’s road network, but interestingly, the effects were more localized. Travel times to and around southeast Nairobi still increased significantly, but travel times to and around some downtown and western areas were actually consistently shorter than the February weekday average in normal weather conditions (Fig 4, below).
This decrease may be the result of a significantly reduced number of vehicles on the road in those areas. In any case, it warrants further investigation in order to understand and plan for the impact and unanticipated effects of future flooding on Nairobi’s road network.
Want to see how March flooding impacted Nairobi in more detail? Explore and download the data for free, on Uber Movement.