The Sahara desert looks about a desolate a place as it is possible to find. Indeed, it is so unpleasant a place to live, that few forms of wildlife can live anywhere but around the perimeter. However, it would appear that this was not the case.
There are various wind currents which carry moisture around the planet. It is unknown why these shift from time to time, but it would appear that one such current used to bring plentiful rain to the Sahara.
Looking at it now, it is hard to believe that this area so harsh to life, might once have been a rainforest. The climate is so incredibly predictable here, it is hard to believe that it was not always like this.
Indeed, there have been cave paintings found in the area, depicting savannah animals including water loving animals such as crocodiles and hippos.
At the moment, it is unclear what caused these ‘rivers in the sky’ to shift so much, but we must recognize that should it happen again, humanity may well have little ability to do anything about it.