Pcic Science Brief 4: Increasing Drought Due to Global Warming in Observations and Models

University House 1, PO Box 1700, STN CSC, University of Victoria, Victoria, British Columbia, Canada, V8W 3R4 Phone: 250-721-6236 | Fax: 250-721-7217 | pacificclimate.org A recent paper by Aiguo Dai (2013) in Nature Climate Change concludes that observed decreases in precipitation and streamflow, as well as increases in drought in certain areas are consistent with model projections of severe1 widespread droughts later in this century. Conditions of decreased precipitation and streamflow are collectively known as aridity. Observational records show an increase in aridity over certain areas since 1950 and climate model projections suggest that this trend will continue into the twenty-first century, though certain areas that have experienced increased wet conditions will see increased aridity and vice-versa. Aridity has increased over Southern Europe, southeast Asia, eastern Australia and most of Africa since the 1950s. Increased wet conditions over northern highlatitude areas, the central United States and Argentina have been observed over the same period. Dai (2013) examined output from models used for the third and fifth phases of the Coupled Model Intercomparison Project2 (CMIP3 and CMIP5, respectively), comparing them against observations over the historical period and examining their projections for the end of the 21st century. For the former, he considered a “medium” greenhouse gas emissions scenario that results in an atmospheric carbon dioxide concentration of 750 parts per million by the year 2100 (SRES3 A1B). For the latter, an atmospheric carbon dioxide concentration of 550 parts per million by year 2100 was assumed (RCP4 4.5), which is roughly double that of the concentration in pre-industrial period (280 parts per million). PCIC SCIENCE BRIEF 4: INCREASING DROUGHT DUE TO GLOBAL WARMING IN OBSERVATIONS AND MODELS