Exploratory: generated automatically from the UmaTerra platforms' data; not independently validated or peer reviewed.

UmaTerra · story Português
Water · city · climate · United States

Katrina, 2005: the city under water and what the maps kept

Hurricane Katrina made landfall on the Gulf coast on 29 August 2005. In New Orleans the storm surge broke levees and floodwalls, and most of the city, which lies below the level of the lake and the river, filled with water. Nine days later Landsat 5 photographed it almost without cloud. This story measures the flood from that picture, asks what two official records of water and land cover kept of it, and reads the climate ahead in climate-shift.

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—of developed land under water on 7 September 2005 estimated
—of the Lower Ninth Ward's developed land under water that day estimated
—of it that the global water map counts as new water measured
—of a 5 km circle within 5 m of the drainage measured

measured by satellite or from the geometry itself. estimated projected by climate models, or a reading that depends on a threshold. missing a part that did not respond this time.

1

A city between a lake and a river

The other UmaTerra platforms (Naturametrics, Camposcope, Yvynation) do not cover the United States. This story runs on climate-shift, which does, and on satellite layers prepared for this page in Earth Engine.

2

What was there before

The Annual National Land Cover Database (USGS) classifies every 30 m pixel of the lower 48 states each year since 1985. climate-shift reads it for any circle in the country.

3

Nine days later, still under water

In short-wave infrared, water is almost black and a leaf is bright. Comparing the scene of 7 September with the one of 22 August separates the ground that went dark with water from what was already river, canal or lake.

4

A water map that does not see the flooded city

JRC Global Surface Water maps, month by month since 1984, every 30 m pixel where Landsat saw water. It is the reference for rivers, lakes and reservoirs around the world.

5

The neighbourhood the land-cover map does not see empty

The Lower Ninth Ward, between the Industrial Canal and St. Bernard Parish, was flooded by the breaches of the canal's floodwall and emptied out for years after. The map shows the 2025 land cover over it.

6

Where the map did record the storm

East of the city lie swamp forest and open marsh. The map shows the 2006 land cover, the first after the storm.

7

The block today

Aerial photographs from the US farm agency (NAIP) see the city house by house, at 2 m in 2005 and 0.3 m today. One frame of the Lower Ninth Ward, before the storm and eighteen years after, set against what the 30 m maps say of the same frame.

8

Low ground

climate-shift reads the terrain of the circle alongside its land cover: steep slopes, ground close to the drainage, water that comes and goes.

9

The climate ahead

For the United States climate-shift uses nine CMIP6 models downscaled by NASA (NEX-GDDP) and forty years of measured climate. The question is which changes this land is exposed to, not when the next storm will come.

10

The future in three readings

A projection compares two 30-year climates, 1985–2014 and 2041–2070, and each model is measured against its own past. climate-shift speaks of a hazard only when at least two-thirds of the models agree on the sign.

11

El Niño, La Niña and the climate ahead

The decades-long trend is not everything: from one year to the next, El Niño and La Niña move rain and heat far more than it does. climate-shift reads the state now from NOAA's relative index (RONI, which does not mistake a warmer ocean for El Niño), groups the October–March seasons already measured here by phase, and then shifts those same seasons by the change projected for 2041–2070. It is an exploratory reading: few seasons per phase, and the models do not agree on how ENSO itself will change.

12

The story, in words

climate-shift also writes its result up in paragraphs, for readers who do not read charts.

13

Where every number came from

Every number on this page came from Earth Engine or from climate-shift's own service, with its source and scale.

umaterra.com.br · Katrina 2005
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What this story does not say

Another story: Palisades, 2025 → The step-by-step walkthroughs

Written with Claude Opus 5.5, by Anthropic, from the numbers Earth Engine and climate-shift computed: no number comes from the model. Versão em português.

Notes

  1. A pixel counts as flooded when on 7 September its SWIR1 reflectance (band 5) is below 0.10 and fell by more than 0.06 since 22 August, it was not water before (MNDWI above 0 on 22 August, or water in more than half of JRC's record), and it sits in a patch of at least ten pixels. Thresholds were chosen by eye against the false-colour scene, so the area is an estimate; a dark roof or a fresh shadow can pass, a shallow puddle under a tree can be missed. USGS Landsat 5 TM Collection 2 Level-2, path 22 row 39.
  2. The JRC water map classifies each Landsat scene with a model trained on open water; a month counts as water if most clear views of the pixel saw it. Under a flooded city the pixel mixes water with roofs and trees, and is not called water. Pekel et al. (2016), Nature 540, 418–422.
  3. “Developed” in the NLCD is land with impervious surfaces at 30 m. Pavement and foundations stay after a house is demolished, so the class holds; only a lot turned to open grass over a whole pixel would move to “developed, open space”. What this map cannot tell, the census and address records can. USGS, Annual NLCD Collection 1 (1985–2025).
  4. climate-shift counts area, not damage. The heavy-rain reading is daily rainfall from the climate models; a hurricane's surge, which broke the levees in 2005, is not in it. Thrasher et al., NASA NEX-GDDP-CMIP6; Yamazaki et al. (2019), MERIT Hydro, Water Resources Research 55, 5053–5073; Biondo, Exposure, not prediction (manuscript in preparation, 2026).
  5. NAIP (National Agriculture Imagery Program) flies each state every two or three years in the growing season. In Earth Engine the Louisiana flights over this block run from 23 June 2005 (2 m) to 4 May 2023 (0.3 m); the 2005 one is the last before the storm. The NLCD impervious fraction is a 30 m estimate of the share of each pixel covered by pavement and roofs. USDA Farm Service Agency, NAIP (public domain); USGS, Annual NLCD Collection 1, fractional impervious surface.