Magical Island question part 2: How to add desert to it

Question

Part number 1 of the question can be found here:

Now I wanted to add a few things just to be on the clear side of things, my world is originally inspired by Brazil. So:

• On the southeast the continent would have the main town (Sao Paulo),
• The south should the coldest area which I want to amplify to make it snowy area (The corresponding area in Brazil is Rio Grande do Sul) (Hence part 1)
• East and half of the center I have a forest (Mata Atlantica) (Henceforth known as Central Forest)
• West and half of the center its the Swamp area (Pantanal)
• Northwest is another forest (Floresta Amazonica) (Technically this is North of Brazil, but I'll get into it later) (Henceforth known as Lost Woods because I'm not THAT creative)
• North is the mountain Region (We technically don't have a mountain region in Brazil, but the highest place - Pico da Neblina - is located North so that's what I'm going with)
• And Northwest would be the desert

The thing with the desert is that it is inspired in the Semi-Arid climate of Brazil's Northeast, initially I thought about making it a desert because it could not receive rain coming from the west side of the continent because of the mountain blockade right next to it. Ideas that I considered for this world:

• Make the north and the south both mountain regions, the middle is a valley. That would solve the initial problem with making the south cold since now I have a mountain + give an explanation to why the northeast is a desert. I could turn the valley into the Mata Atlantica forest and relegate the Swamp to the West of this continent. The problem comes in the form of having two mountain regions and now all of sudden my continent is wider (East-West) and not longer (North-South) as I wanted it in the first place.
• Make a Southwest region. That would be the cold mountain one, you would still have rains coming from the west and that would explain the swamp and eliminate the valley. I like this solution because I could use the south region as something else entirely. I don't like it because I still have the problem from solution number 1 that I'm making the map wider and not longer.

Now, after the whole snow discussion, let's assume the continent is located somewhere next to Argentina, where if you get to enough altitude (2500 m to 3000 m) and having other right circumstances you can get snow most of the year. How could I add in the desert (somewhat realistically) in the Northeast region?

Answer 1

I don't understand some of the snow comments, but maybe I can get you on track.

Deserts don't require drought

Deserts are places where it is hard to grow. Although extreme drought is one way to create a desert, the most common way is to wash away the top fertile layer (erosion). If nothing or little grows, water is hardly retained in the soil. This is because it evaporates quickly, sinks into the ground quickly or simply flows away. The water washes away more fertile soil (if some still remains). This makes it harder for things to grow, which allows water to wash way quicker again, making a self enforcing spiral of desertification.

A desert can start anywhere. It can start right inside a rain forest, providing a large enough area is affected and water isn't retained well enough around it. Although many other area's are more prone to desertification than others.

Answer 2

Just copy Brasil's real climate : it has desertic regions in the northeast

Look for "Lençois maranhenses" on Internet. This is a touristic place on this desert region.