From Glossary of Meteorology
In Thornthwaite's 1931 climatic classification, a humidity province in which the principal plant life is drought-resistant short grasses.
Köppen called these conditions the steppe climate. Semiarid regions are very susceptible to severe drought.
Thornthwaite, C. W. 1931. The climates of North America according to a new classification. Geogr. Rev.. 21. 633–655.
Köppen, W. P., and R. Geiger 1930–1939. Handbuch der Klimatologie. Berlin: Gebruder Borntraeger, 6 vols.