Assessment of future changes in water availability and aridity.

Area of Science:

• Climate Science
• Hydrology
• Earth System Science

Background:

• Future hydrological cycle changes are projected with significant uncertainties.
• The
• dry gets drier, wet gets wetter
• (DDWW) paradigm is a common but potentially oversimplified summary.
• Recent studies question the validity of the DDWW paradigm and the precipitation minus evapotranspiration (P-E) metric for global land surfaces.

Purpose of the Study:

• To comprehensively assess projected changes in the hydrological cycle using CMIP5 models.
• To evaluate the validity of the DDWW paradigm and the P-E metric under future climate scenarios.
• To identify regions experiencing significant hydrological changes and assess their extent.

Main Methods:

• Utilized a comprehensive assessment of Coupled Model Intercomparison Project Phase 5 (CMIP5) data.
• Analyzed projected changes in mean annual precipitation minus evapotranspiration (P-E).
• Evaluated significance of changes across global land surfaces, considering both P-E and aridity metrics.

Main Results:

• Projected changes in mean annual P-E are not significant across most global land areas.
• High-latitude regions are projected to experience wetting conditions by the end of the 21st century.
• Significant increases in aridity are projected for many subtropical and adjacent humid regions, but these do not confirm the DDWW paradigm for most land.

Conclusions:

• The DDWW paradigm is generally not confirmed for projected hydrological changes across most land areas.
• Approximately 70% of land areas are projected to experience no significant changes when combining P-E and aridity metrics.
• Findings highlight the need for nuanced assessments beyond simplified paradigms for understanding future climate impacts.