Vegetation and surface runoff were probably affected by this recent climate variation. Reexamination of several long-term vegetation plots shows that plant density has increased substantially since the early 1970s, probably in response to increased precipitation (R.H. Webb, personal commun., 1999). In addition, surface runoff of overbank-size flow events decreased after at least the early 1950s, as suggested by preliminary studies of runoff frequency (Hereford and Webb, 1997). This probably resulted from less precipitation during the 1942-1977 dry episode and the gradual decline in precipitation intensity. The decrease in the frequency of large runoff events probably influences recharge of shallow aquifers and limits the supply of shallow groundwater.

In conclusion, climate of the Mojave Desert has not been static, rather it has varied substantially in this century, and it is likely to change again in the near future. The problem is understanding whether the magnitude of variation is sufficient to alter the landscape and vegetation. Our ongoing research suggests this recent climate variation has influenced the physical and biological environments of the desert ecosystem.