I can't speak to the Norwegian situation because I know nothing about it. However, I can comment on the Hurricane Katrina situation, having friends who live in that area, knowing a couple FEMA officials (county only, no one high level), having a sister who went down with her church to help with the clean-up and care of the affected people, and in general being such a weather geek that I know a lot about hurricanes and tornadoes.
This is an incredibly complex issue--disaster response is not as simple as 'let's send stuff and get them help." There were definitely system-wide failures that are now being addressed, but I think even if every thing had gone absolutely perfectly, there would still have been widespread devastation that would take months or years to resolve.
Dagobahn makes the comment that there were no plans for evacuation, refugees, or New Orleans itself. That's not accurate. Every city, county, and state is required to have disaster plans and New Orleans, LA, and MS were not exempt. They did have disaster plans, they did order evacuations, and they did have some arrangements in place for refugees. However, the timely and adequate implementation of those plans was sorely lacking.
For Katrina (
http://en.wikipedia.org/wiki/Hurricane_Katrina), there was a constellation of problems that came together to make the disaster far worse than it would have been. Make no mistake--it was bad no matter what was done. However certain actions combined to make the disaster response worse.
First, and most important, the storm itself was unbelievably powerful. New Orleans/LA and MS were not prepared to be hit by the third strongest hurricane to ever hit the US. No one is ever prepared to get hit by a storm that has a 902 mB central pressure at its strongest (most hurricanes have a much higher pressure than this--closer to 1000). When it hit LA, its pressure had only risen to 920mB. The lower the pressure, the higher the storm surge (the wall of water around the eye created by the winds and low pressure), and the stronger the winds whirl around the eye of the storm. At its peak, Katrina had sustained winds of 175 mph (280 kph). When it made landfall, maximum _sustained_ winds were still 120 mph/205 kph. That doesn't include wind gusts which were much higher. The storm had hurricane-strength winds for 150 miles inland, with MS bearing the brunt of the storm. The hurricane-force windfield was huge--240 miles wide in diameter, and the tropical storm force windfield was wider still. So a very large area of MS and parts of LA and AL experienced winds in excess of 75 mph for quite some time.
The storm surge in parts of MS were 28 feet above sea level, and the highest measured storm surge in New Orleans before the sensors failed was 14 feet. The levees were 23 feet above sea level. Imagine a wall of water 3 stories high and you get an idea of how big just the surge was. The actual waves on top of that as best as could be measured were 55.5 feet high--some of the buoys closer to the eye were destroyed by the storm. So, you could have had a wave 82 feet above sea level hitting land (8 stories tall!). This was almost 60 feet higher than the levee height. Even if the waves were not that high when Katrina hit land, the wave heights were still well above the levee height when combined with the storm surge. In addition, it only takes a couple _inches_ of water to move a 2 ton truck. Imagine the sheer power of miles of 80 feet tall waves of water and the massive destruction it could do. In MS, storm surge flowed inland 12 entire miles, flooding everything there.
In addition, the hurricane spawned a number of tornadoes which added to the destruction--51 total, 11 of which were in MS. Rainfall was up to 18 inches in some places. Over a million people were without electricity and natural gas after the storm, and gas stations were flooded and inoperable without electricity. Coastal communities were literally leveled--buildings, trees, everything was flattened. Roads and bridges in the areas hit by the storm were either destroyed or underwater and impassable as a result. I know a paramedic who lives in southern MS, and he noted that they had trouble responding because of the rain, wind, and trees covering the few roads that weren't underwater.
You can have the finest emergency response team in the world, but nothing is going to be able to cope immediately with thousands of square miles of utter physical destruction. The total destruction area was about 90,000 square miles. That's about the size of the entire United Kingdom. The airports in the area were damaged or destroyed. Boats could travel to some degree, but there was a lot of debris in the water that made it dangerous in some spots. Roads were impassable from either water or fallen trees, downed power lines, destroyed bridges, and debris. There were no functioning utilities and no place to get gas or kerosene to power generators. Hospitals and other medical facilities were damaged or outright destroyed. Eighty percent of New Orleans was underwater.
Second, the governments of New Orleans, LA, and the US were slow to respond or in some cases used resources for self-serving reasons rather than search/rescue/disaster response. The US had to wait until states requested federal aid, and the MS governor immediately requested (and received) that aid. The New Orleans Emergency Operations Center was not in a properly prepared building, and it lost phone service, severely affecting communications at the city/county level and made it nearly impossible to communicate immediate needs to the LA EOC. It took the LA governor significantly longer to ask for help, in fact the fed gov't finally used some obscure national emergency plan regulation to finally take over about 48 hours later, although even that response could have been much quicker.
While voluntary evacuations had been ordered, Mayor Nagin did not issue a mandatory evacuation of New Orleans until the 28th of Aug at 10am, even though the Nat'l Hurricane Center had predicted on the 26th that most of the computer models placed the city directly in the path of the storm. The hurricane force winds hit New Orleans 2am on the 29th, only 14 hours after the mandatory order was given, and the hurricane made landfall about 6am, less than 24 hours after the order. Mayor Nagin did not properly implement the city's disaster plan, either. There was not enough gasoline or transports for those who did not have cars, and the plan called for the city's school buses to be used for mandatory evacuations. Dozens of school buses which could have been used for evacuations stood idle and were destroyed in the storm. In spite of that, about 80% of the city did evacuate, or the loss of life would have been much more devastating than it was.
Gov. Blanco of LA moved slowly as well--she did not request aid from the federal gov't for at least 24 hours after the levees were breached, did not request additional Nat'l Guard troops from the Fed. gov't (the Feds can't go in without Gov. approval), and she did not utilize state compacts that allow sharing of Guard troops between states in emergencies.
The Red Cross did a better job of getting resources to a lot of people than the gov't, but whether that was sheer gov't incompetence, fortuitous placement of Red Cross personnel, the extreme travel limitations from the physical destruction, or a combination of the above is unclear. The only way in/out of New Orleans with any reliability for several days was by chopper or small boats. It took time to fly into the city because planes, choppers and other emergency vehicles also had to be evacuated from the area prior to the storm's landfall in order for them not to be destroyed. Keesler Air Force base had to be evacuated of all its planes and choppers prior to the storm making landfall, or they would have been damaged/destroyed--this reduced some air availability. The response time was also limited by the amount of time needed to fly to/from areas where the choppers could land and refuel, which could be a couple hundred miles. In addition, FEMA has been accused of delaying help--waiting for counties or cities to ask for aid rather than just sending it in anticipation of the requests, and even waving off the attempts of civilian aircraft to rescue people the day after the hurricane.
A significant cause of the New Orleans destruction was from the failed levee system. Part of that was the sheer power of the storm, but part of it was that the levee system was aging and funds (local, state, and federal) had not been allocated for modernizing and rebuilding the levee system. There is some question over whether it was built properly in all places, but I suspect it was more a matter of the Army Corps of Engineers using the technology they had available to them at the time it was built and then was not updated. In any case, it was inadequate for something of Katrina's strength.