What could cause skin rashes on the hands each spring?

Hand eczema - common. Allergy to something, but often not identified. Sounds like yours is pretty seasonal. Could be just about anything you come into contact with. Solvents/ metals / occupational exposure / or other typical allergens. Keep a diary to see if there is any association. Treatment is avoidance of irritants including soaps and hot water, hydration, topical steroids...