|Title||The key role of heavy precipitation events in climate model disagreements of future annual precipitation changes in California|
|Publication Type||Journal Article|
|Year of Publication||2013|
|Authors||Pierce DW, Cayan DR, Das T, Maurer EP, Miller NL, Bao Y, Kanamitsu M, Yoshimura K, Snyder MA, Sloan LC, Franco G, Tyree M|
|Journal||Journal of Climate|
|Type of Article||Article|
|Keywords||21st-century; Anthropogenic effects; atmospheric rivers; change impacts; climate; climate change; climate models; ensemble; floods; Model comparison; North America; Regional models; sierra-nevada; simulations; storm tracks; water-resources; western united-states|
Climate model simulations disagree on whether future precipitation will increase or decrease over California, which has impeded efforts to anticipate and adapt to human-induced climate change. This disagreement is explored in terms of daily precipitation frequency and intensity. It is found that divergent model projections of changes in the incidence of rare heavy (>60 mm day(-1)) daily precipitation events explain much of the model disagreement on annual time scales, yet represent only 0.3% of precipitating days and 9% of annual precipitation volume. Of the 25 downscaled model projections examined here, 21 agree that precipitation frequency will decrease by the 2060s, with a mean reduction of 6-14 days yr(-1). This reduces California's mean annual precipitation by about 5.7%. Partly offsetting this, 16 of the 25 projections agree that daily precipitation intensity will increase, which accounts for a model average 5.3% increase in annual precipitation. Between these conflicting tendencies, 12 projections show drier annual conditions by the 2060s and 13 show wetter. These results are obtained from 16 global general circulation models downscaled with different combinations of dynamical methods [Weather Research and Forecasting (WRF), Regional Spectral Model (RSM), and version 3 of the Regional Climate Model (RegCM3)] and statistical methods [bias correction with spatial disaggregation (BCSD) and bias correction with constructed analogs (BCCA)], although not all downscaling methods were applied to each global model. Model disagreements in the projected change in occurrence of the heaviest precipitation days (>60 mm day(-1)) account for the majority of disagreement in the projected change in annual precipitation, and occur preferentially over the Sierra Nevada and Northern California. When such events are excluded, nearly twice as many projections show drier future conditions.
Climate model simulations disagree on whether future precipitation will increase or decrease over California, which has impeded efforts to anticipate and adapt to human-induced climate change. Scripps climate researchers studied a number of climate models and found that heavy daily rainfall events play a disproportionately large role in creating that discrepancy.
Of 25 simulations analyzed by the researchers, 21 project that California will see 6 to 14 fewer days of precipitation by the 2060s, leading to a 5.7 percent decrease in the amount of precipitation. The researchers separately found that 16 of the 25 models agreed that daily rainfall would be more intense, leading to a 5.3 increase in annual precipitation. When such events are excluded, nearly twice as many projections show drier future conditions, according to the researchers.