Plants like aloe vera can be grown on mass with very little work they store water in the dry season. You can dice such plants and feed them to trees or whatever you want to help through the dry season. Putting them in a mulch pit is a good way to put their water content into the soil. You may want to do it before the wet season ends so they can rot a bit. Rotting may cause some adverse effects especially if the roots come into direct contact with the rotting material. It will work well for some plants not so good for others. Dirt should be put on top and then less saturated mulch on top of that.

My plan is to use c3 plants like jade and aloe and also some c 4 plants that tend to hold water a bit later in the year. So first you use the dicon radishes, acanthus and the cana Lillie's then toword the end of the dry season you use you long-term water storage plants like aloe, jade and other c3 plants. You can also collect wet mulch after a heavy dew and impregnate the soil with it covering to seal the moisture in. I guess that would be called dew water catchment.