Both characters mean "dry" - together they describe a state of lacking moisture, whether physical (weather, skin) or figurative (a dry, boring presentation).
Don't confuse 干燥 (gānzào, dry/arid) with 急躁 (jízào, impatient/irritable) or 烦躁 (fánzào, restless/agitated). They share the zào sound but 燥 has the fire radical (火) meaning dryness, while 躁 has the foot radical (足) implying restless movement.
