There are studies worldwide on droughts and their causes. Living in Colorado I have seen the effects of drought on our area. I have also seen the solutions that are so simple that government scientists scoff at them, because they are so simple.
Will the great rivers die? I think it is possible if people don't look at the environment where the rivers start, as well as along their routes to the sea. There are also conservation methods that could make a difference in the amount of fresh water available for people, crops, and wildlife.
I did some research on the Internet on the relation between trees and rain. One site cited the changes in Spain after they cut down all the oak forests to build ships in their efforts to acquire riches from the Americas. Once they had great forests of oaks, and other trees, and plentiful rain. After the trees were cut, primarily for building ships they suffered a drought that lasted many years. Many other places have suffered similar fates, until people started seeing that trees, particularly deciduous, or broad leaf trees.
The great rivers of our world begin in mountains, as small streams fed by snow melt and rainfall. Winding their way down the slopes they gather water from other creeks and streams, growing ever larger on their journey to the sea. As they trickle, babble, and then run their courses, they travel through increasingly populated areas. In these more populous areas people tend to cut down the trees, making room for homes, farms, towns, and cities. This begins many of the problems of fresh water.
In South America we see, and hear about, vast areas of rain forest being clear-cut to make room for fields, without regard to the fact that rain forest soils are very poor for growing crops. The farmers get one or two crops, then go out and cut down, or burn, more trees for more cropland, because the land they originally cleared won't grow anything anymore. Instead of learning how to replenish the land they are setting themselves, and the rest of us, up for droughts and disasters.
Speaking from the standpoint of where I live, I look at the U.S. and see people east of the Mississippi complaining about flooding and severe thunderstorms. At the same time, west of the Mississippi I see little rain, even drought conditions.
Now take a look at the eastern states and compare them to the western states. What do you see that one area has so much more of than the other. The answer is trees, lots of them. Western states could make things better for their residents by planting, and encouraging planting, trees. Not just in cities and towns, but along roadways, in median strips, and in any open space not being used for crops. Even pastures could benefit from trees growing in them, offering shade to livestock on hot days and slowing the winds enough to get snow to pile up and melt into the aquifer. Not just any trees either, but broad leaf trees that are drought, insect, and disease resistant.
Putting dams across washes and gullies, the results of land erosion, would keep water on the land, allowing it to soak down into the aquifers as well. Our water table in Colorado and Kansas is over one hundred feet below what it was at eighty years ago, mostly due to irrigation, population growth, and drought. The rains and snows cannot replenish the water table because there aren't enough storms to soak the ground and fill them. There is also the problem of so many depending on the water to irrigate crops, gardens, and lawns because of so little rain and so many people.
Replenishing the land through fertilizers like manure, legume crops and grasses, and rotted vegetation, better known as compost, can help immensely, anywhere. Planting trees to attract the storms bringing rain and snow can keep the rivers flowing and help provide fresh water for people around the world.
Too simple, and too simplistic, you say? Well, sometimes the simple solutions are the best ones. Collecting tree seeds and planting them is simple. Planting fast growing trees, with slower growing trees nearby, can alleviate drought problems more quickly because the fast growing trees are so fast growing. The good old practice of having rain gutters and rain barrels for water storage could help provide water to get the trees growing better, without using up the limited existing resources. Mulching windbreaks and gardens helps keep the moisture in the soil, saving water too.
All of these ideas can help save our great rivers and forests, while helping drought stricken areas all over. Laugh if you want, but I am planting trees to do my part even if no one else will listen, do the research, and just think about things. If you can come up with better solutions, I'm willing to listen. If you can't, why not try my ideas, they might surprise you!