Once they are established, trees are also very drought hardy, since their roots are deep enough to reach water that annual plants can't. So if you plant fruit and nut trees you will have a food supply even in a drought. So, the quickest way to STOP rain is to clear cut forests. This has been the cause of desertification in many areas of the world, most notably the Middle East and the Sahara Desert. You might say it's a tall order to reforest a place where it has stopped raining - since there is no water for the trees.
Swales are basically just level trenches dug into the ground.
Since they are level, when it rains the rainwater is captured in the swales and seeps deep into the soil. After one rainy season enough water is stored in the soil beneath the swale, to support a tree during the dry spells till it gets going. The Village Homes community in Davis, CA is a great example of a treed oasis in the middle of a dryland - without using anything but rainwater captured in swales. There are lots of other ways to store water against drought - in ponds, cisterns and the like. But once trees get established, it creates a microclimate where there is much more precipitation than in surrounding areas with no trees.