Feb 16, 2017

Precipitation in a warming world: Assessing projected hydro-climate changes in California and other Mediterranean climate regions

by
Suraj D. Polade, Alexander Gershunov, Daniel R. Cayan, Michael D. Dettinger, David W. Pierce
,
Scientific Reports
  • States that in most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures
  • States that in California, however, projections of changes in annual precipitation are inconsistent
  • Analysis of daily precipitation in 30 GCMs reveals patterns in projected hydrometeorology over each of the five MedClm regions globally and helps disentangle their causes
  • Finds that MedClim regions, except California, are expected to dry via decreased frequency of winter precipitation
  • Finds that frequencies of extreme precipitation, however, are projected to increase over the two MedClim regions of the Northern Hemisphere where projected warming is strongest
  • Finds that the increase in heavy and extreme precipitation is particularly robust over California, where it is only partially offset by projected decreases in low-medium intensity precipitation
  • Finds that over the Mediterranean Basin, however, losses from decreasing frequency of low-medium-intensity precipitation are projected to dominate gains from intensifying projected extreme precipitation
  • States that MedClim regions are projected to become more sub-tropical, i.e. made dryer via pole-ward expanding subtropical subsidence
  • States that California’s more nuanced hydrological future reflects a precarious balance between the expanding subtropical high from the south and the south-eastward extending Aleutian low from the north-west
  • Concludes that these dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events