There are in Spain races of sheep that eat some very strange things like the super tough grass that they use to make rope soled shoes, esparto or stipa tenacissima, which is a dry place grass.
In places with a dry season the plants dry off in summer but grow back in winter, grass dies back and the leaves fall of the trees.
Different grasses have different systems for surviving adverse seasons, some have
underground rhizomes which survive drought or cold that have buds on them, the buds grow and re-establish the plant when the rains comes. Some grasses die back nearly all their
roots and aerial parts drying except for tiny buds at ground level protected in the middle of dry sheaths of grass, these buds too sprout with the rains. Look up Raunkiaer's system of living forms for information on this. You don't have to water them in summer though they look dead they will reappear when the rains come. but don’t let live stock eat the dry grass to the ground or they will do for the buds that allow it to recover.
What about saffron, that is a bulb and they only appear in spring and die back afterwards so they don’t mind dry summers?
Grasses, like oats and wheat are annuals but bamboos, that are also graminoids can be very long lived, not all the grasses that dry in summer are annuals, a lot are grasses live various years though they appear dry in summer they relive with the rains.
Water harvesting on the land.
You can build a underground cistern that takes the run off from a floor that you construct as a catchment area. A hundred square meters’ or yards of floor by a half inch of rain how much water is that, i don't know i hate maths but a fair amount to run a micro-drip irrigation system on maybe. How much land do you have by the creek to catch rainwater on?
In sandy soils you want to build up lots of vegetable matter so they have something in them that will hold onto the water which runs straight through sand. The continually dying and regrowing roots and stems of the grass that will grow there are the easiest way to build up organic matter in the soil.
Mulch turns into organic matter in the soil that gives sand some consistency but as mulch, that is as a layer of dead leaves say, that covers the ground, leaves that the rain can work under, what it does is to prevent the rain being reabsorbed by the air, mulch lessens surface evaporation.
Light showers can end up in very little because of runoff and surface evaporation.
Think how much of the rainfall that falls evaporates off the ground again and you will understand the importance of shading the ground, of ground plants provide shade and bushes and trees even more shade.
Trees are always a awy of reducing the cold and wind as well as of having shade.
Plants absorb water through their leaves and stems so if you have plants around less of the water of a light
shower of rain will evaporate off.
As water gets carried through sand easily, the nutrients get carried with it so sand can lack nutrients.
On the other hand in hot countries where there is not much rainfall to wash through the ground and so in doing to wash salts out of the ground, the ground can salt up easily if you apply nutrients to it. That goes for manure as well as chemical fertilizers, only as it is harder to spread manure it is more unusual for people to apply too much chemical fertiliser.
Growing nitrogen fixing plants is one way of increasing the nitrogen in the soil for example legume type trees. I don’t know which ones you have in the Americas, real acacias, like mimosa, are very dry area leguminous plants and the false ones that are American, that is two groups of
nitrogen fixing trees robinas and gleditsias of American are nitrogen fixing trees of America that I do know. There are brooms that live in dry countries and they are leguminous. Nearly all leguminous plants have nodules on their roots that fix nitrogen and as you have water nearby and trees are long rooted their roots should get to the water. Manyt of the nitrogen ficing trees are also usefull as forage for live stock. Paul Wheaton’s normal suggests cow peas with buck wheat which are a very deep rooted dry country sort of bean unless i am wrong and they should be a good at fixing nitrogen.
In places where it is very hard to grow food the people usually live on live stock that can eat the tough plant that can grow in these places, the trouble is they often get the live stock overgraze the land and so they reduce the plants they can
feed off.
In the south of Europe and north of Africa they grow winter vegetables in green houses for the whole of Europe.
Look up
brad Lancaster who does
permaculture in Tucson Arizona, he knows about desert plants. He has posted videos in you tube. Also the you tube video
greening the desert by Geof Lawton. You should whatch all three of
bill mollison's you tube dryland strategy videos
bill mollison dryland strategies they include a description of makng a floor that will catch water for an underground cistern . He does not make a very big floor. agri
rose macaskie.