I live in rio de janeiro and I'm thinking about starting a hugel raised garden bed because I'm imagining there will be no irrigation at all in this particular terrain. The thing is I have no information of hugels in tropic humid climates such as here, I've read that they raise soil temperture which is probably going to have a negative impact when summer comes with almost every day being 40 degrees celsius. I think usually a hugel wouldnt be necessary but we are going through really bad dry years here (probably due to amazon rainforest deforastation for cattle grazing), so that water holding capacity would really come in handy. So, do you think a hugelkultur is adequate for tropic really hot not so humid climate? Have you got any materials for it on tropics?
I can read spanish fairly well (cause my native tongue is portuguese), but english is still better for me.
I don´t think the temperature inside the hugel will rise that much. In much colder climates there might be a noticeable difference but in the tropics it might not be that much. It all also depends on the materials you use for building the hugel: if you use too much "green" (nitrogen rich) materials the whole thing can decompose and compost faster leading to higher temperatures but if you use more carbon rich materials this can be controlled. A hugel is not a compost pile, it should rather decompose slowly over time providing years of fertility.
Another aspect to consider is the orientation of the hugel relative to the sun and wind. If you set it up properly the hugel will have warmer and cooler areas, so it could in fact help you create cooler microclimates by providing shade and protect your plants from the high temperatures. Try to make it curvy instead of straight. Also mulch it heavily so it stays "insulated" from the external heat and it will probably stay cooler on the inside than the outside ambient.
You already know the main benefit: It will reduce the need for irrigation and stay moist inside for weeks.
As for materials, just use what you have at hand and can obtain locally and cheaply, that's the beauty of it.