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Houston flood footprint released

JBA HAS DEVELOPED A FLOOD EVENT FOOTPRINT OF THE FLOODING IN HOUSTON IN APRIL 2016. THE DATA COMPRISE AN EVENT MAP OF INDICATIVE FLOOD DEPTHS ON A 30M GRID.

Intense and prolonged rainfall fell over Texas in mid-April 2016 due to slow-moving storm systems. High river flows resulted, and severe flooding was reported in Houston.

Meteorological description

Texas experienced record-breaking rainfall in April 2016 after two storm systems passed over the area on 17 and 18 April. A blocking high pressure system caused the storm systems to stall over Texas and intense thunderstorms delivered heavy rainfall.

At Houston Intercontinental Airport (Houston’s official weather observation site), 9.92 inches (252 mm) of rainfall was recorded on 18 April, corresponding to three times the monthly average for the whole of April, and equal to the total average rainfall for February, March and April combined. For this location, 18 April was the second wettest calendar day on record (in a series from 1888) and April 2016 was already the wettest April on record by the 21st.  

Figure 1: Rainfall totals for the period 15 to 18 April (Global Precipitation Measurement mission).

Satellite-based estimations of rainfall over Texas between 15 and 18 April 2016 are shown in Figure 1. Rainfall totals reached 12 inches (300 mm) during this three-day period.  

Figure 2: Precipitation totals for the one-week period 15 - 22 April 2016 (NOAA).

Figure 3: River flows in cubic feet per second for Brays Bayou, in Houston, Texas (USGS).

Observed precipitation totals for the period 15 and 22 April reached 18 inches (457 mm) in Texas, between the major cities of Austin and Houston (see Figure 2).

The heavy rainfall led to high flows throughout Texas. On the Brays Bayou in Houston, the flow peaked on 18 April, reaching over 20,000 cubic feet per second. The median daily flow at this gauge is around 90 cubic feet per second (see Figure 3).

Figure 4: Brays Bayou on a normal day (left) and Brays Bayou on 18 April (right) Mark Sudduth @hurricanetrack

Figure 5: Flooding from Buffalo Bayou in Houston on 18 April (bottom) and the same location before the flooding (top) (Jacqueline Stallings @LivingLola).

River flooding was reported in Texas. Worst affected was Houston, where rivers burst their banks and more than 1,200 people were rescued from the rising floodwaters. Over 110,000 homes and businesses in Houston were without electricity during the storms, and the electricity restoration efforts were hampered due to numerous road closures.

A flash flood warning was announced by the National Weather Service on the morning of 18 April which covered a region encompassing more than 21,000 square miles, the largest in at least the last decade. A disaster declaration was made for at least nine counties in southeast Texas and several emergency shelters were opened in Harris County, which includes Houston. At least eight fatalities were attributed to the floods.

JBA’s Houston flood event footprint

JBA's footprint of the event (shown in Figure 6) was developed in three stages as follows:

  1. Monitor river levels and flood extent
  2. Extract design hazard map for river flooding
  3. Cross-reference return period to knowledge of defence breaches, local effects, imagery and claims data

Figure 6: Footprint of the flooding in Houston in April 2016.

If you'd like to know any more about the Houston flood footprint please get in touch.