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Urbanization causes increased cloud base height and decreased fog in coastal Southern California

TitleUrbanization causes increased cloud base height and decreased fog in coastal Southern California
Publication TypeJournal Article
Year of Publication2015
AuthorsWilliams A.P, Schwartz R.E, Iacobellis S., Seager R., Cook B.I, Still C.J, Husak G., Michaelsen J.
JournalGeophysical Research Letters
Date Published2015/03
Type of ArticleArticle
ISBN Number0094-8276
Accession NumberWOS:000351847600034
Keywordsclimate change; climate model; coastal california; dense fog; feedback; fog; los-angeles; marine boundary-layer; patterns; sea-surface temperature; stratus; summer fog; united-states; urban heat island; urban-growth

Subtropical marine stratus clouds regulate coastal and global climate, but future trends in these clouds are uncertain. In coastal Southern California (CSCA), interannual variations in summer stratus cloud occurrence are spatially coherent across 24 airfields and dictated by positive relationships with stability above the marine boundary layer (MBL) and MBL height. Trends, however, have been spatially variable since records began in the mid-1900s due to differences in nighttime warming. Among CSCA airfields, differences in nighttime warming, but not daytime warming, are strongly and positively related to fraction of nearby urban cover, consistent with an urban heat island effect. Nighttime warming raises the near-surface dew point depression, which lifts the altitude of condensation and cloud base height, thereby reducing fog frequency. Continued urban warming, rising cloud base heights, and associated effects on energy and water balance would profoundly impact ecological and human systems in highly populated and ecologically diverse CSCA.

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