Michael Mann, a climate scientist at Penn State, has posted a long (for Facebook) article on Facebook about how climate change contributes to events like this. In short, climate determines the probability of a particular weather event occurring, but ultimately any one particular weather event is a roll of the (now slightly loaded) dice. Warmer water and warmer air than in the past have both made events like this more likely, and are making events like this more destructive when they do occur. The article has links to several journal articles which would be worth reading to know something about hydrology and climate change. But right now I can’t do that because I’m late for my job where I have to convince people I know something about, among other topics, hydrology and climate change.
Sea level rise attributable to climate change (some is due to coastal subsidence due to human disturbance e.g. oil drilling) is more than half a foot over the past few decades (see http://www.insurancejournal.com/…/sou…/2017/05/31/452704.htm for a decent discussion).
That means that the storm surge was a half foot higher than it would have been just decades ago, meaning far more flooding and destruction.
In addition to that, sea surface temperatures in the region have risen about 0.5C (close to 1F) over the past few decades, from roughly 30C (86F) to 30.5C (87F), which contributed to the very warm sea surface temperatures (30.5-31 C or 87-88F). There is a simple thermodynamic relationship known as the “Clausius-Clapeyron equation (see e.g. https://en.wikipedia.org/…/Clausius%E2%80%93Clapeyron_relat…) that tells us there is a roughly 3% increase in average atmospheric moisture content for each 0.5C (~1F) of warming. Sea surface temperatures in the area where Harvey intensified were 0.5-1C warmer than current-day average temperatures, which translates to 1-1.5C warmer than the ‘average’ temperatures a few decades ago. That means 3-5% more moisture in the atmosphere.