Significantly Wetter or Drier Future Conditions for One to Two Thirds of the World’s Population

Source: Nature Communications

Introduction

Future projections of precipitation are uncertain, hampering effective climate adaptation strategies globally. This article summarizes the findings from the Nature Communications article “Significantly wetter or drier future conditions for one to two thirds of the world’s population” by Ralph Trancoso et al. (2024). The study introduces an approach that detects agreement in drier and wetter conditions by evaluating continuous 120-year time-series with trends, across 146 Global Climate Model (GCM) runs and two elevated greenhouse gas (GHG) emissions scenarios. The study addresses the challenge of coherence across models by using a novel approach that avoids excessive temporal averaging, which can obscure critical information.

In Short

• Future Rainfall: Some areas will get much wetter or drier, affecting billions of people.
• Policy Action: Governments need to plan for these changes to manage water resources effectively.

Methodology

The study evaluates long-term trends in precipitation using a novel approach that avoids excessive temporal averaging, which can obscure critical information. The methodology involves:

1. Data Collection: Using 146 GCM runs from CMIP5 and CMIP6 under intermediate (RCP4.5/SSP2-4.5) and high (RCP8.5/SSP5-8.5) emissions scenarios.
2. Trend Analysis: Applying non-parametric trends using the Mann-Kendall test and Theil-Sen Slope to detect and quantify changes over a 120-year period.
3. Agreement Detection: Assessing the percentage of models that agree on the direction and magnitude of trends, focusing on regions where at least 50% of the models show significant trends.

Simplified

• Data Collection: Researchers used data from numerous climate models to get a comprehensive view of potential future changes in rainfall.
• Trend Analysis: They examined long-term changes in rainfall patterns without excessive averaging, revealing clearer trends.
• Agreement Detection: They assessed how many models concurred on whether a region would become wetter or drier in the future.

Results and Findings

Key Findings

1. Hotspots of Change: The study identifies regions with significant agreement on future drying or wetting trends. For example, Greece, Spain, and Morocco show strong drying trends, while Finland, North Korea, and Canada show strong wetting trends. The Caribbean and Mediterranean regions are particularly impacted by drying, while high latitudes and parts of Asia and Central Africa show wetting trends.
2. Population Impact: Approximately 3 billion people (38% of the current global population) are projected to be affected under an intermediate emissions scenario, and 5 billion people (66% of the world population) under a high emissions scenario by the century’s end. This includes both drying and wetting impacts.
3. Seasonal Variability: The study also highlights seasonal dominance in precipitation changes, with different regions experiencing varying impacts across seasons. For instance, the southwest coast of Australia and the Indian Ocean are dominated by SON (September-October-November) precipitation trends, while the Iberian Peninsula is dominated by JJA (June-July-August) trends.

Simplified

• Wetter or Drier: Some regions will get much drier (like Greece and Spain) or much wetter (like Finland and Canada) in the future.
• Population Impact: Billions of people will be affected by these changes, with more people impacted under higher emissions scenarios.
• Seasonal Changes: Different regions will see changes in rainfall during different seasons, affecting local climates in various ways.

Practical Implications

For policymakers and local administrators, the findings suggest:

• Adaptation Strategies: Regions identified as drying or wetting hotspots should prioritize water management and infrastructure adaptation.
• Policy Development: Policies should be informed by the projected changes in precipitation to mitigate risks associated with water scarcity or excess.
• Community Engagement: Local communities should be educated about the potential impacts and involved in developing adaptive strategies.

What We Know and What We Don’t

What We Know

• Projected Changes: There is a high level of agreement among models about the direction of precipitation changes in certain regions, with clear hotspots of drying and wetting.
• Population Impact: A significant portion of the global population will be affected by these changes, necessitating proactive adaptation measures.

What We Don’t Know

• Regional Specificity: While the study provides a broad overview, more localized studies are needed to understand specific regional impacts, especially in areas with high internal variability.
• Model Limitations: The inherent uncertainties in climate models mean that projections should be interpreted with caution. The study uses a robust approach, but the diversity of model outputs still presents challenges.

Where to Learn More

For further information, you can access the full article and supplementary materials:

• Nature Communications Article
• Supplementary Data
• Code and Datasets

Authors

The study “Significantly wetter or drier future conditions for one to two thirds of the world’s population” is authored by Ralph Trancoso, Jozef Syktus, Richard P. Allan, Jacky Croke, Ove Hoegh-Guldberg, and Robin Chadwick. Their collective expertise spans several institutions, including The University of Queensland, University of Reading, and the Met Office Hadley Centre.

Access the Paper

The full paper is available for download at Nature Communications.