Alfalfa is also drought tolerant and growing as ground cover plant, but all in all i would go for more shrubby N-fixig plants. Elaeagnus gives you a good choice of drought tolerant shrub species serving also as wind protection and edible fruits. There are others n-fixing and drought tolerant shrubs and trees out there.
This is
Geoff Lawton's list of pioneer plant species used on the site Jordan
"If you came to a site like this and just started planting typical fruit and vegetables, you would fail miserably. Conditions are far too harsh. Without pioneer species (like these listed below) first setting the stage, the show just would not go on."
Leacaena: a fast growing, medium size and life span tree; a very heavy nitrogen fixer and very high quality animal forage that coppices and pollards very well.
Sesbania sesban: an extremely fast growing small tree with a short life span; a very heavy nitrogen fixer, grows very easily from seed.
Albizia lebbek: a slower growing, long-term, large canopy, long-lived shade tree; a good nitrogen fixer and very drought tolerant.
Tipuana tipu: a slower growing, long-term, large canopy, long-lived shade tree, with excellent filtered shade form for food forest canopy inter-planting; a good nitrogen fixer and moderately drought tolerant. Will coppice or pollard.
Prosopis: a medium to large tree, long-lived, a good nitrogen fixer, a good forage including the pods which can be human food; coppices and pollards well but is very spiny and is usually pruned to a high standard to reduce human contact with the spines, unless being used as an animal barrier hedge or for
firewood production as it is quite good stick fuel for rocket stoves. Extremely drought tolerant.
Aciacia Farnesiana: a small, medium-term nitrogen fixing tree with food,
medicinal, dye and perfume uses; also a thorny barrier plant. Very drought resistant.
Poinciana: a large and beautiful flowering and exotic leaf form, very wide canopy long-lived nitrogen fixer that will coppice and pollard. Quite drought tolerant.
Acacia Saligna: a small medium-term nitrogen fixer, fast growing, good fire
wood, very drought tolerant.
Bauhinia: a very beautiful flowering plant with an unusual leaf, a slower growing, large canopy, long-lived shade tree; a good nitrogen fixer and moderately drought tolerant. Will coppice or pollard.
Honey Locust: a long-term, medium-size nitrogen fixer that is very thorny; will coppice and pollard and is very good firewood and a very good bee forage.
Jerusalem Torn: a medium to large long-lived tree, a good nitrogen fixer, small thorns, very hardy with light shade canopy.
Casuarina Torulosa: a fast-growing, long-lived, tall, slender form nitrogen fixer and phosphate fixer through fungi relationship; a very good wind break tree and excellent firewood.
Cassia: a small,
local bush cassia that is a medium-term nitrogen fixer that can be cut for mulch.
Tecom Stans: a medium-size and -term fast growing, very hardy tree that can be heavily coppiced or pollarded for mulch. Not a legume.
Pig Face: a succulent ground cover that insulates the ground from the intense heat, reducing evaporation and trapping organic matter and wind blown nutrient, creating a much improved topsoil environment. Extremely drought tolerant.
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Anyway, here's the top ten out of my list - all easy, common and effective:
