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Bytnerowicz, A, Cayan D, Riggan P, Schilling S, Dawson P, Tyree M, Wolden L, Tissell R, Preisler H.  2010.  Analysis of the effects of combustion emissions and Santa Ana winds on ambient ozone during the October 2007 southern California wildfires. Atmospheric Environment. 44:678-687.   10.1016/j.atmosenv.2009.11.014   AbstractWebsite

Combustion emissions and strong Santa Ana winds had pronounced effects on patterns and levels of ambient ozone (O(3)) in southern California during the extensive wildland fires of October 2007. These changes are described in detail for a rural receptor site, the Santa Margarita Ecological Reserve, located among large fires in San Diego and Orange counties. In addition, O(3) changes are also described for several other air quality monitoring sites in the general area of the fires. During the first phase of the fires, strong, dry and hot northeasterly Santa Ana winds brought into the area clean continental air masses, which resulted in minimal diurnal O(3) fluctuations and a 72-h average concentration of 36.8 ppb. During the- second phase of the fires, without Santa Ana winds present and air filled with smoke, daytime O(3) concentrations steadily increased and reached 95.2 ppb while the lowest nighttime levels returned to similar to 0 ppb. During that period the 8-h daytime average O(3) concentration reached 78.3 ppb, which exceeded the federal standard of 75 ppb. After six days of fires, O(3) diurnal concentrations returned to pre-fire patterns and levels. Published by Elsevier Ltd.

Stahle, DW, Griffin RD, Therrell MD, Edmondson JR, Cleaveland MK, Stahle LN, Burnette DJ, Abatzoglou JT, Redmond KT, Meko DM, Dettinger MD, Cayan DR.  2009.  The ancient blue oak woodlands of California. Fremontia. 37:22. AbstractWebsite
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Stahle, DW, Griffin RD, Meko DM, Therrell MD, Edmondson JR, Cleaveland MK, Stahle LN, Burnette DJ, Abatzoglou JT, Redmond KT, Dettinger MD, Cayan DR.  2013.  The ancient blue oak woodlands of California: Longevity and hydroclimatic history. Earth Interactions. 17   10.1175/2013ei000518.1   AbstractWebsite

Ancient blue oak trees are still widespread across the foothills of the Coast Ranges, Cascades, and Sierra Nevada in California. The most extensive tracts of intact old-growth blue oak woodland appear to survive on rugged and remote terrain in the southern Coast Ranges and on the foothills west and southwest of Mt. Lassen. In the authors' sampling of old-growth stands, most blue oak appear to have recruited to the canopy in the middle to late nineteenth century. The oldest living blue oak tree sampled was over 459 years old, and several dead blue oak logs had over 500 annual rings. Precipitation sensitive tree-ring chronologies up to 700 years long have been developed from old blue oak trees and logs. Annual ring-width chronologies of blue oak are strongly correlated with cool season precipitation totals, streamflow in the major rivers of California, and the estuarine water quality of San Francisco Bay. A new network of 36 blue oak chronologies records spatial anomalies in growth that arise from latitudinal changes in the mean storm track and location of land-falling atmospheric rivers. These long, climate-sensitive blue oak chronologies have been used to reconstruct hydroclimatic history in California and will help to better understand and manage water resources. The environmental history embedded in blue oak growth chronologies may help justify efforts to conserve these authentic old-growth native woodlands.

Stahle, DW, Therrell MD, Cleaveland MK, Cayan DR, Dettinger MD, Knowles N.  2001.  Ancient Blue Oaks reveal human impact on San Francisco Bay salinity. EOS Trans. AGU. 82:141,144-145. Abstract
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Shukla, S, Steinemann A, Iacobellis SF, Cayan DR.  2015.  Annual drought in California: Association with monthly precipitation and climate phases. Journal of Applied Meteorology and Climatology. 54:2273-2281.   10.1175/jamc-d-15-0167.1   AbstractWebsite

Annual precipitation in California is more variable than in any other state and is highly influenced by precipitation in winter months. A primary question among stakeholders is whether low precipitation in certain months is a harbinger of annual drought in California. Historical precipitation data from 1895 to 2013 are investigated to identify leading monthly indicators of annual drought in each of the seven climate divisions (CDs) as well as statewide. For this study, drought conditions are defined as monthly/annual (October-September) precipitation below the 20th/30th percentile, and a leading indicator is defined as a monthly drought preceding or during an annual drought that has the strongest association (i.e., joint probability of occurrence) with a statewide annual drought. Monthly precipitation variability and contributions to annual precipitation, along with joint probabilities of drought among the winter months, are first analyzed. Then the probabilities of annual drought and the variability in leading indicators are analyzed according to different climate phases and CDs. This study identified December within a water year as being the leading indicator that is most frequently associated with annual drought statewide (56%) and in most of the CDs (the highest was CD2 at 65%). Associated with its leading-indicator status, December drought was most frequently associated with drought in other winter months (joint probability > 30%). Results from this study can help stakeholders to understand and assess the likelihood of annual drought events given monthly precipitation preceding or early in the water year.

Ely, LL, Enzel Y, Cayan DR.  1994.  Anomalous North Pacific atmospheric circulation and large winter floods in the Southwestern United States. Journal of Climate. 7:977-987.   10.1175/1520-0442(1994)007<0977:anpaca>2.0.co;2   AbstractWebsite

Specific anomalous atmospheric circulation conditions over the North Pacific are conducive to the occurrence of the largest winter floods (greater-than-or-equal-to 10-yr return period) on rivers in six hydroclimatic subregions of Arizona and southern Utah, Nevada, and California. Composite maps of anomalies in daily 700-mb heights indicate that floods in all of the subregions are associated with a low pressure anomaly off the California coast and a high-pressure anomaly in the vicinity of either Alaska or the Aleutian Islands. Of these two major circulation features, the presence of the low is the controlling factor in determining whether large floods will occur. Shifts in the locations of the low and high pressure anomalies over the North Pacific appear to control which subregions experience floods, with high-elevation topographic features and proximity to air masses forming a major influence over the specific atmospheric circulation conditions that generate large floods in each hydroclimatic region. Concerning the interannual variability of flooding in the Southwest, there is an increased frequency of large winter floods during multiple-year periods dominated by negative SOI and a virtual absence of large floods during the intervening periods. This suggests that global-scale climatic anomalies exert a strong influence on the occurrence of severe regional winter floods.

Rodo, X, Ballester J, Cayan D, Melish ME, Nakamura Y, Uehara R, Burns JC.  2011.  Association of Kawasaki disease with tropospheric wind patterns. Scientific Reports. 1   10.1038/srep00152   AbstractWebsite

The causal agent of Kawasaki disease (KD) remains unknown after more than 40 years of intensive research. The number of cases continues to rise in many parts of the world and KD is the most common cause of acquired heart disease in childhood in developed countries. Analyses of the three major KD epidemics in Japan, major non-epidemic interannual fluctuations of KD cases in Japan and San Diego, and the seasonal variation of KD in Japan, Hawaii, and San Diego, reveals a consistent pattern wherein KD cases are often linked to large-scale wind currents originating in central Asia and traversing the north Pacific. Results suggest that the environmental trigger for KD could be wind-borne. Efforts to isolate the causative agent of KD should focus on the microbiology of aerosols.

Nemani, RR, White MA, Cayan DR, Jones GV, Running SW, Coughlan JC, Peterson DL.  2001.  Asymmetric warming over coastal California and its impact on the premium wine industry. Climate Research. 19:25-34.   10.3354/cr019025   AbstractWebsite

Climatic changes over coastal California from 1951 to 1997 may have benefited the premium wine industry, as seen in higher quality wines and larger grape yields. Observed temperature warming trends were asymmetric, with greatest warming at night and during spring. Warming was associated with large increases in eastern Pacific sea surface temperatures (SST) and amounts of atmospheric water vapor. Although the average annual temperature warming trend was modest (1.13degreesC/47 yr), there was a 20 d reduction in frost occurrence and a 65 d increase in frost-free growing season length. In the Napa and Sonoma valleys, warmer winter and spring temperatures advanced the start of the growing season by 18 to 24 d, and enhanced atmospheric water vapor resulted in a 7% reduction in evaporative demand. Given the strong coupling between Pacific SSTs and the coastal California climate, and because regional-scale SSTs persist for 6 to 12 mo, additional research may allow the possibility of predicting vintage quantity and quality from previous winter conditions.

Enzel, Y, Cayan DR, Anderson RY, Wells SG.  1989.  Atmospheric circulation during Holocene lake stands in the Mojave Desert: evidence of regional climate change. Nature. 341:44-47.   10.1038/341044a0   AbstractWebsite

IT is commonly thought that the climate conditions that supported lakes over a period of years in the Mojave Desert in southern California, only existed before 8,000 yr BP and that the environment has been arid since1,2. Here we look at a drill core in the Silver Lake playa at the terminus of the Mojave River and find Holocene lake deposits which indicate that shallow lakes existed for at least a few decades. These deposits were radiocarbon dated at 3620 ±70 and 390 ± 90 yr BP, corresponding to the early Neo-glacial and the 'little ice age' respectively3. To identify the conditions necessary to produce these Holocene lake events we have examined the modern climate and hydrological patterns that produce ephemeral lakes in this usually arid watershed. Available data indicate that there is a link between anomalous winter atmospheric conditions over the North Pacific and Mojave River floods that produced ephemeral lakes in the Silver Lake playa and that the Mojave River filters out small to medium floods and allows only the extreme floods to reach the terminal playa and leave a record of the anomalous conditions. We suggest that the late Holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods.

Pierce, DW, Barnett TP, Hidalgo HG, Das T, Bonfils C, Santer BD, Bala G, Dettinger MD, Cayan DR, Mirin A, Wood AW, Nozawa T.  2008.  Attribution of declining western US snowpack to human effects. Journal of Climate. 21:6425-6444.   10.1175/2008jcli2405.1   AbstractWebsite

Observations show snowpack has declined across much of the western United States over the period 1950-99. This reduction has important social and economic implications, as water retained in the snowpack from winter storms forms an important part of the hydrological cycle and water supply in the region. A formal model-based detection and attribution (D-A) study of these reductions is performed. The detection variable is the ratio of 1 April snow water equivalent (SWE) to water-year-to-date precipitation (P), chosen to reduce the effect of P variability on the results. Estimates of natural internal climate variability are obtained from 1600 years of two control simulations performed with fully coupled ocean-atmosphere climate models. Estimates of the SWE/P response to anthropogenic greenhouse gases, ozone, and some aerosols are taken from multiple-member ensembles of perturbation experiments run with two models. The D-A shows the observations and anthropogenically forced models have greater SWE/P reductions than can be explained by natural internal climate variability alone. Model-estimated effects of changes in solar and volcanic forcing likewise do not explain the SWE/P reductions. The mean model estimate is that about half of the SWE/P reductions observed in the west from 1950 to 1999 are the result of climate changes forced by anthropogenic greenhouse gases, ozone, and aerosols.