Glen M. MacDonald
Department of Geography UCLA
Southern California and the Perfect Drought: Simultaneous Prolonged Drought in Southern California and the Sacramento and Colorado River Systems
Southern California relies heavily upon imported water from the Sacramento and Colorado river systems to augment local supplies and to mitigate the impacts of drought. A ‘perfect drought’ is defined as a prolonged drought that affects southern California, the Sacramento River basin and the upper Colorado River basin simultaneously (See MacDonald et al. California Department of Water Resources 2005 and MacDonald et al, Quaternary International, 2007).
Examination of instrumental climate and discharge records shows that over the past century such perfect droughts do occur, but generally persist for less than five years. Perfect droughts that extend across all three areas are associated with anomalous upper-level high pressure off west coast and over western North America which is in turn associated with anomalously cool eastern Pacific sea surface temperatures.
Exploratory tree-ring reconstructions of winter Palmer Drought Severity in southern California, annual discharge of the Sacramento River and annual discharge of the Colorado River demonstrate that prolonged perfect droughts (~30 to 60 years), which produced arid conditions in all three regions simultaneously, developed in the mid-11th century and the mid-12th century during the period of the so called ‘Medieval Climate Anomaly’. Prolonged aridity in western North America during this period appears to have been associated with cooling of the eastern equatorial and North Pacific related to the differential thermal response of the western and eastern Pacific to increased tropical radiative forcing at that time. This potential linkage between positive radiative forcing and prolonged perfect droughts raises serious concerns regarding the hydrological impacts of future climate warming in southern California and the West.
Global warming could produce prolonged perfect droughts impacting all of southwestern North America due to the increased subsidence of dry and warm air in the subtropics (see Seager et al., Science, 2007). This general drying trend could be coupled with cooling of the eastern tropical Pacific Ocean relative to the western tropical Pacific to produce truly perfect droughts - which in the past have lasted decades.
This page highlights the Perfect Drought concept and research conducted
by Glen MacDonald's lab at UCLA
CURRENT YEAR SUMMER DROUGHT CONDITIONS (July, 2007) - US Drought Monitor map shows Perfect Drought pattern in West. http://drought.unl.edu/dm/monitor.html
SOUTHERN CALIFORNIA WATER REACH - Map of Southern California water sources (compare sources of water to current drought map and 2005 and 1998-1991 drought maps). MacDonald, G.M. 2007. Severe and sustained drought in Southern California and the west: Present conditions and insights from the past on causes and impacts, Quaternary International. doi:10.1016/j.quaint.2007.03.012.
DEMANDS ON THE COLORADO RIVER - Natural flow variability and long-term average flow of Colorado River and population growth of the cities of Los Angeles, Phoenix and Las Vegas. MacDonald, G.M. 2007. Severe and sustained drought in Southern California and the west: Present conditions and insights from the past on causes and impacts, Quaternary International. doi:10.1016/j.quaint.2007.03.012.
21st CENTURY DROUGHT - State of western drought in 2005. MacDonald, G.M. 2007. Severe and sustained drought in Southern California and the west: Present conditions and insights from the past on causes and impacts, Quaternary International. doi:10.1016/j.quaint.2007.03.012.
IMPACT LAST BIG DROUGHT - Drought conditions during last mini-Perfect Drought (1988-1992). Negative values indicate drought (compare to current and 2005 conditions). MacDonald, G.M., Kremenetski, K.V. and Hidalgo, H. 2007. Southern California and the Perfect Drought: Simultaneous Prolonged Drought in Southern California and the Sacramento and Colorado River Systems. Quaternary International. doi:10.1016/j.quaint.2007.06.027
ATMOSPHERE AND OCEAN DURING 1988-1992 DROUGHT - Persistent 700 mb high pressure anomaly and cool eastern tropical Pacific sea surface temperature anomaly (Jan. 1988-Dec. 1991). MacDonald, G.M., Kremenetski, K.V. and Hidalgo, H. 2007. Southern California and the Perfect Drought: Simultaneous Prolonged Drought in Southern California and the Sacramento and Colorado River Systems. Quaternary International. doi:10.1016/j.quaint.2007.06.027
ANCIENT PERFECT DROUGHTS - Medieval mega-drought during the 11th and 12th centuries causing drought in southern California (negative values of Palmer Drought Severity - PDSI), and simultaneous low-flows on the Sacramento River and the Colorado River for up to ~60 years. The grey series are annual estimates and black series are 5-year moving averages. The grey vertical bars highlight the two widespread drought pulses apparent in the reconstructions during the Medieval Climate Anomaly. MacDonald, G.M., Kremenetski, K.V. and Hidalgo, H. 2007. Southern California and the Perfect Drought: Simultaneous Prolonged Drought in Southern California and the Sacramento and Colorado River Systems. Quaternary International. doi:10.1016/j.quaint.2007.06.027
WARMING
WARM CLIMATE, COOL EASTERN PACIFIC AND PERFECT DROUGHT - Estimated cool temperature departures for NINO3 (eastern Pacific el Nino conditions) (Mann et al., 2005), negative state of the Pacific Decadal Oscillation (PDO - cool temperature conditions in northeastern Pacific (MacDonald and Case, 2005), southern California winter drought represented by Palmer Drought Severity Index (PDSI) and combined negative annual discharge departures for the Sacramento and Colorado rivers during the Medieval mega-droughts. Climate warming at that time seems to have caused the cooling of the eastern Pacific and other factors that produced prolonged drought. The grey series are annual estimates and black series are 5-year moving averages. The grey vertical bars highlight the two widespread drought pulses apparent in the reconstructions during the Medieval Climate Anomaly. MacDonald, G.M., Kremenetski, K.V. and Hidalgo, H. 2007. Southern California and the Perfect Drought: Simultaneous Prolonged Drought in Southern California and the Sacramento and Colorado River Systems. Quaternary International. doi:10.1016/j.quaint.2007.06.027
Selected Drought References from MacDonald Lab
MacDonald, G.M. 2007. Hot and dry - for decades. Los Angeles Times, July 13, p. A21. http://www.latimes.com/news/printedition/opinion/la-oe-macdonald13jul13,1,4424613.story?coll=la-news-comment
MacDonald, G.M., Kremenetski, K.V. and Hidalgo, H. 2007. Southern California and the Perfect Drought: Simultaneous Prolonged Drought in Southern California and the Sacramento and Colorado River Systems. Quaternary International. doi:10.1016/j.quaint.2007.06.027
MacDonald, G.M. 2007. Severe and sustained drought in Southern California and the west: Present conditions and insights from the past on causes and impacts, Quaternary International. doi:10.1016/j.quaint.2007.03.012.
MacDonald, G.M. and Rian, S. and Hidalgo, H. 2005. Southern California and the “perfect drought”. In Colorado River Basin Climate. California Department of Water Resources. 50-57. http://watersupplyconditions.water.ca.gov/co_nov05.pdf
MacDonald, G.M. 2005. Water supply. Southern California Environmental Report Card, UCLA Institute of the Environment. 4-11. www.ioe.ucla.edu/RC05.pdf
MacDonald, G.M., Case, R.A. 2005. Variations in the Pacific Decadal Oscillation over the past millennium. Geophysical Research Letters. 32, L08703, doi10.1029/2005GL022478.
MacDonald, G.M., Rian, S., Hidalgo, H. 2005. Southern California and the “perfect drought”. In Colorado River Basin Climate. California Department of Water Resources. Sacramento, 50-57.
Case, R.A., MacDonald, G.M. 2003. Tree ring reconstructions of streamflow for three Canadian Prairie rivers. Journal of the American Water Resources Association 39, 703-716.
Hidalgo, H.G., Dracup, J.A., MacDonald, G.M. and King, J.A. 2001. Comparison of tree species sensitivity to high and low extreme hydrologic events. Physical Geography 22: 115-134.
MacDonald, G.M. and Case, R.A. 2000. Biological evidence of multiple temporal and spatial scales of hydrological variation in the western interior of Canada. Quaternary International 67: 133-142.
Szeicz, J.M. and MacDonald, G.M. 1996. A 930-year ring-width chronology from moisture sensitive white spruce (Picea glauca Moench) from northwestern Canada. Holocene, 6:345-351.
Case, R.A. and MacDonald, G.M. 1995. A dendroclimatic reconstruction of annual precipitation on the western Canadian Prairies since A.D. 1505 from Pinus flexilis James. Quaternary Research, 44: 267-275.
Larsen, C.P.S. and MacDonald, G.M. 1995. Relations between tree ring widths, climate and annual area burned in the boreal forest of Alberta. Canadian Journal of Forest Research, 25: 1746-1755.