Born in the town of Niemegk near Bitterfeld, Rauh studied at Biology faculty at the University of Halle under the famous morphologist Wilhelm Troll and received his doctorate in Botany in 1937 before coming to the University of Heidelberg two years later. He discovered or described some 1200 genera, species and varieties of plants from Africa, the Americas and Asia. His fields of specialization were the Bromeliads and succulent plants. He was a Professor at the University of Heidelberg and Director of the Institute of Plant Systematics and Plant Geography as well as Director of the Heidelberger Botanical Gardens and authored over 300 scholarly books and articles. His work on the succulent and xerophytic flora of Madagascar is presented in his two-volume work Succulent and Xerophytic Plants of Madagascar.