What Daily Nighttime Lights Can and Cannot Show About Power Outage and Recovery: Winter Storm Uri in Harris County, Texas

Daily nighttime light (NTL) images are widely used to map power outages and recovery, but clouds and quality screening leave gaps. We examined what NASA Black Marble data show about the February 2021 Winter Storm Uri outage in Harris County, Texas. When only high-quality retrievals were used, 16 February was the only usable night during the outage, and the next were 19 to 21 February. On 16 February, 5112 of 13,846 developed pixels (37%) were below half their pre-storm brightness, and 92% of those with an observed return were lit by 21 February. Return dates between these nights are unobservable. Recovery dates from a detector-based workflow depend on smoothing, persistence and aggregation choices; in a controlled experiment with known recovery dates and flag-0 observations only, an unsmoothed rule requiring three consecutive calendar nights has a median detection delay of 12 to 15 days. Compared with 20 ordinary clear nights, 16 February dimming was far more extensive and clustered. However, the estimated average total impact of the Social Vulnerability Index was 10.6 percentage points of reference radiance (95% interval −32.0 to 49.8), within the range estimated on ten ordinary pre-storm nights (−31.9 to 26.8). Single-night community comparisons need an ordinary-night baseline.