Flood Frequency of the Mojave River and the Formation of Late Holocene Playa Lakes, Southern California, USA

Perennial lakes lasting several decades occupied Silver Lake playa, the terminus of the Mojave River, as recently as 390 ± 90 and 3620 ± 70 BP. Flood routings from the Mojave River headwaters to its terminal playa, and water balance calculations for the resulting lakes, indicate that floods comparable in magnitude to the largest floods in the modern record must occur almost annually to generate and maintain perennial lakes. In contrast, the modern floods of this magnitude have recurrence intervals greater than 18 years. Such an increase in flood frequency is required even if lake evaporation is reduced by as much as 50%. Modern extreme floods of the Mojave River are related to meridional atmospheric circulation and a southeastward shift in the winter low pressure center over the North Pacific Ocean, causing vigorous storms over the headwaters in the San Bernardino Mountains of southern California. This winter pattern probably occurred more frequently to induce the large number of storms and floods needed to form the middle and late Holocene lakes in Silver Lake playa.