On the evening of September 1, 2021, the remnants of Hurricane Ida struck New York City, bringing widespread flooding that produced hundreds of millions of dollars of damage and claimed the lives of 13 people within the City. The storm had already been reclassified as a post-tropical cyclone after having affected much of the Northeastern United States, but it still shattered the City’s record for the most single-hour rainfall at 3.15 inches. Inclement weather conditions continued until September 3, with an estimated total downfall of over 7 inches of water.

For context, the City’s sewer system, which handles both waste and rain runoff in a single pipe, only has the capacity to handle 1.75 inches of rain per hour. Water exceeding that capacity accumulated in streets and spilled over into the subway system, cellars, and basements — disproportionately impacting the 100-year floodplain in which 93.1% of Ida-impacted buildings are situated. The unprecedented downpour violently exposed the stark climate vulnerabilities that pervade New York City, with the extreme degree of calamity attributed to the overloaded, century-old drainage system that was ill-equipped to accommodate the exceptional rainfall rates brought forth by Ida.

Needless to say, much of the City’s transportation was brought to a standstill. Torrents filled the BQE, FDR, and even a ramp to the Brooklyn Bridge. 80 tractor-trailers, trucks, and cars were also abandoned on the Bronx’s Major Deegan Expressway, as motorists were stranded by leaking retaining walls along the 8.5-mile highway. Passengers on 15 to 20 subway cars had to be rescued in the storm as waterfalls emerged within subway stations across all five boroughs — ranging from Harlem’s 116th Street station to Jefferson Street’s L train.

Transportation workers at the Metropolitan Transportation Authority tirelessly conducted round-the-clock repairs to restore operations to the nation’s largest subway system. Yet on September 3, two days after the wake of Ida, most of the city’s subway lines remained disrupted by delays and partial suspensions. At the same time, bicycles prevailed as a resilient form of transportation in the midst of extreme weather recovery. On September 2, Citi Bike witnessed 126,360 rides — breaking its single-day ridership record at the time.

Analyzing Citi Bike System Data over the duration of August 29 to September 4 (the full week during which Ida took place), 2021, may allow us to better understand how Hurricane Ida had impacted cyclist behaviors and ridership patterns — and how disrupted mobility networks may have been mediated by the availability of Citi Bike service. Given the inequitable coverage of the bike-sharing system throughout the five boroughs, it is hypothesized that ridership may be concentrated in Manhattan. Moreover, the extreme and anomalous nature of Hurricane Ida may instigate higher usage of Citi Bikes by non-Citi Bike members. Finally, while Citi Bike infrastructure is built to be protected from blackouts or storm-related electrical shortages, it is hypothesized that Ida may have been met with diminished electric bike compared to classic bike usage.

A plummet in Citi Bike usage is, predictably, observed on September 1, at 50,554 total rides. The day afterward, the number of rides surged to 125,810 — the deviation from Citi Bike’s reported figure of 126,360 is attributed to the removal of rides that omit longitude or latitude information in this analysis. After stratifying the figures by membership status, it reveals that the surge may be specifically attributed to an increased number of casual riders, as the number of riders with memberships had remained relatively comparable between August 31 versus September 2.