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

Suraj D Polade,David W Pierce,Daniel R Cayan,Alexander Gershunov,Michael D Dettinger

doi:10.1038/s41598-017-11285-y

Suraj D Polade, David W Pierce + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-11285-y

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Abstract

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. 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. MedClim regions, except California, are expected to dry via decreased frequency of winter precipitation. Frequencies of extreme precipitation, however, are projected to increase over the two MedClim regions of the Northern Hemisphere where projected warming is strongest. 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. Over the Mediterranean Basin, however, losses from decreasing frequency of low-medium-intensity precipitation are projected to dominate gains from intensifying projected extreme precipitation. MedClim regions are projected to become more sub-tropical, i.e. made dryer via pole-ward expanding subtropical subsidence. 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. These dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events.

Highlights

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures
This study focuses on late-21st Century winter (Northern Hemisphere–NH: December-January-February or DJF; Southern Hemisphere–SH: June-July-August or JJA) precipitation changes relative to the late 20th Century in five Mediterranean regions around the globe – the Mediterranean basin (MED), South America (SAA), California (CAL), South Africa (SAF), and Australia (AUS)
Using daily projections from 30 CMIP5 global climate models forced by the RCP 8.5 scenario during the period of 2060–2089 relative to the period of 1960–1989, we investigated changes in winter precipitation in five MedClim regions around the globe, which are mostly robustly projected to become drier

Summary

Introduction

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. 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 These dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events. 10 explained trends towards wetter California by a lengthening of the intermediate-scale stationary waves in the presence of accelerated sub-tropical westerlies These previous studies of future precipitation primarily resolved annual to seasonal time scales, focused on California alone, and mainly investigated dynamical mechanisms. As we shall see, compared to other MedClim regions, seasonal precipitation projections over California are characterized by uncertainty This uncertainty stems in part from two opposing and robust signals: decreased frequency and increased intensity of projected daily precipitation[5]. We aim to achieve a clearer understanding of projected precipitation over California than is implied by the large model spread in annual precipitation

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