The ability of an invasive species to acquire and use a limiting resource during critical life history stages governs its ability to establish and persist within an environment. Arid environments are generally considered more resistant to invasion and are defined by low and sporadic precipitation. Warm-season grasses are most susceptible to mortality during seedling emergence, but water requirements for emergence are rarely known. We examined the ability of the often invasive warm-season grass, buffelgrass, to emerge given a range of simulated precipitation delivered on 2, 3, and 4 consecutive days with the use of a line-source irrigation system in a glasshouse. The minimum amount of water required for buffelgrass emergence was observed to be 6.3 mm (3.14 mm on 2 consecutive days). With the use of probit analysis, the median emergence response (0.5 emergence probability) was predicted to require 17.4–19.9 mm of water. Emergence was concentrated within the first 5 days following initial simulated precipitation with the probability of new emergence highest on Days 3 and 4. Over the period from 1949–2001 in Tucson, Arizona within the Sonoran Desert, the total number of consecutive rainy-day sequences meeting the minimum per-day precipitation levels for a median and minimum emergence response was 27 and 92, respectively. Precipitation sufficient to result in emergence of 50% of viable buffelgrass caryopses has occurred in Tucson in about 1 of 2 years over this period. We compare the soil water requirements for emergence of buffelgrass to other perennial species in the Sonoran Desert and suggest that the invasion success of buffelgrass is due in part to its ability to emerge following relatively low precipitation levels.