Reconciling the Discrepancy in Projected Global Dryland Expansion in a Warming World

Area of Science:

• Climate Science
• Hydrology
• Environmental Science

Background:

• Continental drying and dryland expansion are linked to environmental degradation and desertification.
• Current aridity index assessments conflict with observations of greening and increased runoff, questioning drying trend accuracy.
• Warming world projections of continental drying and dryland dynamics require accurate assessment methods.

Purpose of the Study:

• To reassess continental drying trends and dryland expansion by correcting potential evapotranspiration (PET) overestimation.
• To resolve discrepancies between observed environmental changes and projected drying trends.
• To provide accurate projections of global dryland dynamics under climate change.

Main Methods:

• Utilized an energy-based potential evapotranspiration (PET) estimator to bias-correct the aridity index.
• Compared drying trends derived from the corrected aridity index with those from widely used Penman equations.
• Analyzed ecohydrological and hydroclimate projections from 32 climate models using the corrected aridity index.

Main Results:

• Continental drying is considerably weaker and less extensive (47% of global land area) than previously estimated (61%-65%) using Penman equations.
• Dryland expansion is projected to affect only 2.1% of global land area even in a high-emission scenario.
• Corrected aridity index and model projections show no significant change in the extent of global drylands.

Conclusions:

• The widely used Penman equations significantly overestimate potential evapotranspiration (PET), exaggerating continental drying trends.
• Global dryland expansion is less extensive than previously projected, with significant implications for environmental degradation assessments.
• These findings resolve the debate on global dryland expansion and improve understanding of climate system impacts on terrestrial ecosystems.