When people think of deserts they think of natural deserts like the Sahara, which have been created by hot dry winds sucking out all the water from the land, making it impossible for anything to grow. Or perhaps the tundra deserts near the Arctic circle, which are so cold and dry that again, nothing grows.
A desert is simply a place where nothing grows, and yes, humans can create them, in places where there is plenty of rain.
The following picture is of a lakeside in Iceland.
Lake shores are normally wooded thanks to the close availability of water that seeps into the sides of the lake. But this one is completely barren, nothing grows there.
Iceland is the site of the world's worst ecological disaster. When the Vikings arrived there a thousand years ago, a quarter of it was thickly wooded with birch and other trees. We know this both from the Icelandic sagas, which provide vivid descriptions, and from the archaeological record.
But the Vikings (whom we now call Icelanders) proceeded to cut the trees down to make room for farms and sheep, and the island slowly started to desertify. Today just 1% of Iceland is wooded, and despite heroic efforts over the last two decades to regreen it, not much progress is being made. They have rain, they have people planting shrubs and trees, but still struggle to make things grow.
The reason is to do with soil. Most of the food we grow is grown on top soil which sits on top of the bare rocks. In fertile areas of the world, this top soil is thick and rich. In other areas it is thin and can only support a few hardy plants. In Iceland it is non-existent.
Top soil is made of organic material (decaying plants), and is normally full of living things - worms, bacteria, fungus, which play a big part in turning dead plants into compost. This soup of composted organic material and tiny organisms is what gives soil it's fertility and enables crops (and other plants) to grow. The mulch also holds water so that when it rains, some of the water sits in the top soil and allows plants to slowly sip it and be sustained, even during dry weather.
However if you cut down all your trees, and let sheep graze the land so severely that they eat away all the grass including the roots, then there is nothing to hold the topsoil in place. Strong winds and rain will blow it away or wash it away, till nothing exists anymore apart from the rock, which is barren in that it has no carbon material in it and no worms or other living organisms present. And thus nothing that can sustain life, no matter how much it rains.
The Icelanders have learned through painful experience that if they want to re-green their island, they first need to lay down a thick layer of soil, cover it with grass to hold the soil in place and then plant shrubs and trees amongst the grass. And protect the whole lot from sheep so they can grow.
Human created deserts are growing across the world due to soil erosion and over grazing. China is the worst modern example. Through carelessness and over grazing, northern China has turned into desert, so much so that the wind is now eroding the bare rocks and turning it into sand which regularly blows into Beijing.
China is no longer self-sufficient in food because of desertification, which is why their threats not to buy food from the American breadbasket are so hollow.