Devastating floods in Rio Grande do Sul, Brazil’s southernmost state, have killed at least 95 people and displaced 150,000 more. NASA Earth Observatory posted the above Landsat 8 image of downtown Porto Alegre (population: 1.5 million), as well as MODIS images of the overflowing Jacuí River. CNN has before-and-after Maxar imagery of Porto Alegre.

As the CBC’s evening news program The National reports, flood maps can be incredibly hard to find, with even municipal maps requiring an NDA to view in some cases. Now this story focuses on Halifax, Nova Scotia in the wake of flash flooding this summer; the situation elsewhere in Canada may be quite different (Quebec’s flood maps, for example, are available online, though only in French).

NASA Earth Observatory has before-and-after satellite imagery showing the impact of the destruction of Ukraine’s Kakhovka Dam last month. The Kakhovka Reservoir is emptying out (above), the irrigation canals that relied on that reservoir are drying out, and there was flooding downriver of the dam in the immediate aftermath of the breach.

The satellite imagery of the flooding in Pakistan is insufficient to grasp how widespread the devastation is, unless you zoom out enough (which you can do at the MODIS page). The imagery focuses on the flood plain of the Indus River: it covers most of Sindh province and a good chunk of Baluchistan. See The Washington Post’s maps for perspective. The Earth Observatory and MODIS pages, as well as the CNN article, have before/after image sliders: Earth Observatory compares the situation to three weeks ago, the other two to last year.

Update, 1 Sept:

The ESA has released the above image based on Copernicus Sentinel-1 data. More than a third of Pakistan is now under water.

Update, 3 Sept: The Guardian has more before/after imagery.

In the wake of serious and devastating spring flooding in 2017 and 2019, the Quebec government issued proposed flood zone maps that marked areas where rebuilding and new construction would be put on hold. There was immediate pushback: as CBC News reported last month, the maps included substantial areas of small towns (such as, in my neck of the woods, the villages of Fort-Coulonge and Campbell’s Bay), or, in the case of Gatineau, areas that were not flooded in either 2017 or 2019 as well as major new developments. The mayor of Vaudreuil-Dorion suggested that the mapmakers forgot to correct for cloud cover. In the end, new maps were issued that removed substantial areas of Montreal from the flood zone, among other areas: some 20 percent of the 120,000 homes affected by the first set of maps were removed from the revised maps.

Previously: Quebec Flood Maps.

Fast forward to this spring. The flood maps for Montreal-area municipalities have been updated—they’re now based on LIDAR data from 2014 onward—but have not yet made public: they’ve yet to be approved by the municipalities or adopted by the province; nonetheless they’ve been put to use during the recent emergency. On the new maps, some 1,500 homes in Sainte-Marthe are part of the flood zone.

And, via CityLab, here are a set of maps from the Urban Institute that show the impact of Hurricane Harvey on Houston’s neighbourhoods, based on income levels, home ownership rates, accumulated-equity rates, all of which looking at the economic impact of the storm. “Harvey’s aftermath puts an enormous hurdle in front of all homeowners and renters but will be a particular setback for low-income, minority families recovering from the 2008 housing bust.”

Previously: Mapping Hurricane Harvey’s Impact.

The Washington Post maps rainfall and flooding levels in the Houston area.

The New York Times is collecting several maps on two web pages. The first page deals with subjects like rainfall, river level, current and historical hurricane tracks, damage reports, and cities and counties under evacuation orders. Maps on the second page look at Harvey’s impact on the Houston area.

Esri’s U.S. Flooding Public Information Map includes precipitation and flood warnings.

#Harvey in perspective. So much rain has fallen, we've had to update the color charts on our graphics in order to effectively map it. pic.twitter.com/Su7x2K1uuz

— National Weather Service (@NWS) August 28, 2017

Kenneth Field critiques the National Weather Service’s decision to add more colours to their precipitation maps (see above). “Simply adding colours to the end of an already poor colour scheme and then making the class representing the largest magnitude the very lightest colour is weak symbology. But then, they’ve already used all the colours of the rainbow so they’re out of options!”

NASA Earth Observatory: “Days of intense rainfall in August 2016 led to widespread flooding in southern Louisiana, as rivers swelled high above their banks and many crested at record-high levels. […] The animation above shows satellite-based measurements of the rainfall as it accumulated over the southern United States. Specifically, it shows rainfall totals every three hours over the span of 72 hours from August 12-14, 2016. These rainfall totals are regional, remotely sensed estimates, and local amounts can be significantly higher when measured from the ground.”

These two Landsat images illustrate the extent of flooding along the Wabash and Illinois Rivers at the end of last year, as 6-10 inches of rain fell over the midwestern United States. The image from 8 December 2015, above left, shows normal water levels; the image from 1 January  2016, above right, shows the rivers in flood. Use the slider to compare the two views. Original image. [via]

• Evacuation zone maps from the City of Calgary, in PDF format.
• For a wider view, an interactive map of Calgary evacuation zones from CBC News.
• A map of flooding zones across Alberta.
• A flood report map from the Calgary Herald, using reader submissions.
• A mobile site for crowdmapping flood reports (thanks, Matt).

Update, 10:15 PM:

• The Alberta provincial government’s Flood Hazard Map Application; requires Flash (via Colby Cosh).

Update, June 22 at 8:25 AM:

• Google’s Alberta Flooding Crisis Map.