God's Judgment
Noah was declared by God to be righteous and perfect in his generations, so when God decided to judge the world or at least Noah's portion of the world, depending on your interpretation and use of synecdoche where all may be referred to for a part, Noah and his family and a selection of animals were saved in the ark God directed him to build.
Once the rains had stopped and the floods had abated, Noah and all of the animals left the ark. At this point, Noah offered a sacrifice to God in thanks for his and for his family's salvation and for food to eat. I'm pretty sure that Noah's opinion of God as worthy and awesome played into the immediate sacrifice as well. Noah's sacrifice touched God's heart. God determined that He wouldn't destroy the world's living creatures again completely by flood even though the heart of man was desperately wicked.
There have been many natural catastrophes since the time of Noah's flood, and there will be many more continuing through the tribulation with its pestilence, hail, and earthquakes to name a few. But in all the time since, the world hasn't come close to being destroyed by flood which was the only reservation God made at this time.
God has judged mankind for their sin after the flood. Sodom and Gomorrah were destroyed by fire from heaven, for example. So the people of the world didn't get a free pass forever and some judged particularly wicked paid a pre-eternal price even after the flood. But God did choose to not destroy all humanity and animal life again by flood and proceeded to communicate this to Noah.
The Rainbow Token
As a token of His commitment to mankind, God pointed out a rainbow to Noah and said that it would be a token of his covenant forever. When God saw the rainbow, He would remember His commitment to not destroy the world by flood again. Noah and all his descendants could also look on the rainbow and remember God's promise that another flood was not coming. Now God didn't need the reminder, but man did.
There are debates among some Christians as to whether or not rainbows were a new thing after the flood or not. I don't believe they were new. They were simply something beautiful you could look at and remember God's promise sometimes after it rained. He took something that existed and tied it forever to his covenant with mankind and other living things that they were safe from being flooded out by God's wrath.
Rainbows are pretty cool things. In order to see one, you need to be in the right place at the right time. But some things are true, regardless. In order for a rainbow to appear, there needs to be a source of light behind you. You won't see a rainbow when it is dark because it is the light - generally from the sun - that creates it in the first place. Two people in the same place at the same time should be able to see the same rainbow. But two people in different spots might not both see the rainbow depending on angles and the light's position.
If you are really lucky, you might see a double rainbow. If you see a second rainbow, it's color sequence will be reversed from the first and it will be dimmer than the primary rainbow.
But the light has to be in a proper frame of reference relative to your eye for a rainbow to appear at all. If there isn't an approximate 40 degree spread, it just isn't seen. Physics is cool.
But back to the promise. When a rainbow is seen it generally means the storm is mostly passed or moved on. The sun is beginning to shine even if it is dark where you are. The world hasn't been destroyed. Even if a person you know can't see the rainbow, you can tell them it is there and that there is hope. A flood may have brought destruction to your world. You may be in a position where you know that you cannot recover from the damage. But the world and the people of the world go on. You go on even if others might not. And that is all that God promised by the rainbow. All living things will not be destroyed.
Why Does Destruction Happen
God still gets blamed for many things. There are many ways nature can mess up your life. Fire, rain, drought, hail, blizzard, sleet or ice, flood, earthquake, mudslide, tsunami, tornado, hurricane, typhoon, monsoon, or just high wind, super-volcano, volcano, meteor or comet strike, extremes of temperature or some combination thereof are a few. People who have been in nature's path frequently lash out at God. If God cared, this wouldn't have happened, they say. How could He have let this happen to me or our community.
God did not make the choice for sin to come into the world. That was a decision that Adam and Eve made. And even if the world hadn't suffered a curse because of that, I'm willing to bet that very few people take the time to pray about where they should live in the first place. Most simply live where their parents lived or in the same general vicinity. Others have gone where the work is, without once asking God if they should follow the work or go someplace else or do something else. If you don't ask God what He wants you to do or where He wants you to go, or listen when He tells you, how can you blame Him if something bad happens where you chose to domicile? Even those who asked at some point in time, rarely ask again unless something gives them a reason to move in the first place.
Finally, many people know the risks of where they have chosen to live, even if they didn't ask God about any of it in the first place. Still, they choose to live in risky places because there is something they like there - it's close to the beach, the forest is pretty and quiet, the lake is great for boating, it's close to downtown, or the cost of living in safer places is simply too high - for example. God cannot be blamed for any of those choices if they put you more at risk than other places. Beach areas or flat areas near the coast are at risk for hurricanes and tidal surge actions or the beach might gradually erode, putting your house in the water. Proximity to forests or grasslands puts you at risk for fires. Places with risks of hail or tornado have their own issues but tornado alley is a thing. They are more numerous in particular spots and are stronger there as well. Homes in flood plains are likely to get flooded out from time to time, and of late with increasing frequency. If you know about these risks, it is up to you to reduce the risk as much as you can, but if you choose to take the risk or don't choose to build accordingly, it is wrong to blame God when the x% chance event happens.
And surprisingly, many times rain is associated with the natural disaster, and there is a rainbow that can be seen. Extreme heat and drought or high winds without a thunderstorm are some of the few exceptions that don't at least have the potential for a rainbow. Most others might pull storms in along with them or after where God's covenant symbol might be seen.
Other Rainbows
But we need to realize that there are many more trials and problems we will experience in our lives than just those due to nature. In many cases, there are the equivalent of rainbows that we can look for in the situation to indicate that the trial has passed.
If you are in or have been in an abusive situation, the abused frequently can see the storm coming. Most times they have no place they feel they can go and hope for the best. Once the abuse is in progress, history with the abuser gives them an idea of when the rainbow will shine and the abuse will be over for this time. When you see the storm on the horizon, find help for yourself and anyone else who is affected. Don't wait to see if you survive the storm. Find someplace safe to go. Find or build your own ark in preparation and use it. Christians need to rise up and help protect the innocent. If you avoid the storm altogether, then you don't have to look for the rainbow to signal the storm has passed.
Work problems and debt storms take people frequently. In many of these you can see or know from history when the storm is coming, and you can see the rainbow of when the financial storm has passed. Sometimes these storms can't be avoided, but sometimes changes in lifestyle can help keep the damage from the storm to a minimum. You can put yourself in the position of seeing the storm's rainbow quicker. Or you can alter your behavior either at work or before work or after work so your risk of work problems is less. Whenever you can avoid a storm completely instead of just shortening its duration, you've won a battle.
In other cases, the Holy Spirit can counsel you when you are in a storm and let you hear His promise that a rainbow is ahead even if you cannot see it or don't know what to look for. If you are not alone in the storm, and the Holy Spirit tells you there is a rainbow and the storm is over, tell those you are with. Let them know that God has told you the storm is over and there's a rainbow out there for all of you.
When the next crisis arises, remember all of the rainbows that you have seen physically or God has impressed on you in your life. When others are in storms that don't affect you personally, take the time to talk to them about your own storms and rainbows and let them know that God does care for them. Remember that He cares for you as well.
Some storms are long. Some seem to have no end. I'm sure that Noah felt that way after his long time stuck in an ark with a lot of critters to feed and clean up after. But the end will come. If it doesn't come before you die, and you're a Christian, know that there probably aren't any bad storms in heaven. Rainbows would still be awesome though, even in heaven. Trust in your Savior, and know that He draws nigh to you through the Holy Spirit's presence in your life. Trust Him to bring you to the other side of any storm you are in. Look for His rainbows and trust them when you see them.