Hurricane Harvey may not compare with the widespread devastation caused by this year's monsoon rains in India, but it is likely to become the costliest natural disaster in US history.

Hurricane Harvey made landfall more than a week ago and is now the wettest tropical system to hit the contiguous US.

Some parts of eastern Texas have had more than a metre of rain.

The resulting floods are ongoing and will remain so for some time to come. Even on Saturday, the mayor of Houston ordered a mandatory evacuation for about 4,600 residences in the western part of the city where several hundred people have not left their homes damaged by the flooding caused by Hurricane Harvey.

''Because people are choosing to stay even after I'm asking them, we've been asking them to leave, I have no choice but to issue a mandatory evacuation for those individuals who are living in homes or in apartments in this particular area, who have chosen to remain in place,'' said Mayor Sylvester Turner, adding that residents should also consider the safety of first responders who would have to handle any emergencies.

The storm has displaced more than one million people, leaving behind wreckage in an area stretching more than 480km.

Some areas of Texas received more than 1,310mm of rain and the storm led to the deaths of at least 53 people.

Houston has now suffered three "500-year floods" in the last three years. Despite that fact, Scott Pruitt, President Trump's head of the Environmental Protection Agency, says that it is "misplaced" to talk about Harvey and climate change.

Climate change will make hurricanes worse. These tropical systems arise from warm waters where temperatures are at least 27 Celsius.

The waters in the Gulf of Mexico are currently more than 30C in places and are generally two or three degrees above the long-term average.

Warm air can hold more moisture than cooler air, so it follows that rainfall will be heavier and storms will be more intense.

The remnants of Harvey are now clearing the northeastern United States and blue skies have now brightened up the flood-hit south.

However, there are still a few showers in the forecast for Louisiana and eastern Texas over the next two days. The high waters will remain in place a good deal longer.