One difference is the geography and size.

Harris County, which includes Houston, is the third most-populous county in America, with 4.5 million people. Miami-Dade County has 2.7 million people, and is the country’s seventh biggest. Houston is roughly 50 miles from the Gulf of Mexico, while Miami and its string of islands and keys are at the doorstep of the Atlantic Ocean.

Because of that geography, officials in Florida are more battle-tested and prepared for hurricanes than those in Texas. The last time a Category 4 hurricane made landfall in Texas was 1961; the benchmark hurricane experience for many Floridians remains the Category-5 Hurricane Andrew in 1992.

The situation was also different in Texas and Florida because of the two hurricanes themselves. Houston officials said Hurricane Harvey was not on course to strike the Houston region with destructive winds and storm surge, but was predicted to drop massive amounts of rain. When it comes to potential flooding from heavy rainfall, so-called sheltering-in-place remains the preferred emergency preparedness model, because it is far more dangerous to venture into floodwaters than to remain at home and call for help.

The direct hit from Hurricane Harvey was expected to be, and indeed turned out to be, the Corpus Christi area, roughly 200 miles southwest of Houston.

Irma’s threat to the Miami-Dade region was more direct. Irma was forecast for a direct or near-direct hit on the cities and counties in the region, with destructive winds and a powerful tidal surge. The sheltering-in-place model used in Houston would put millions of people in jeopardy if used in the Miami-Dade area.

“The danger is being blown away, the danger is being cut in half by flying debris that’s going 175 miles per hour,” said Natalie Simpson, an emergency response expert who is a professor of operations management at the University at Buffalo in Buffalo, N.Y. “Flooding is very, very dangerous, but you can scramble for higher ground. It’s not so immediately lethal.”

In Houston, one issue that played a background role in the decision to not order an evacuation was the memory of Hurricane Rita in 2005. The highways out of Houston were clogged for hours in that evacuation. Thousands of motorists ran out of gas or slept in their cars, and more than 20 nursing home residents died after they evacuated the Houston area and their bus caught fire on Interstate 45 in a Dallas suburb.