Enhanced spring warming in a Mediterranean mountain by atmospheric circulation

Area of Science:

• Environmental Science
• Climate Science
• Ecology

Background:

• Cévennes National Park, Southern France, is a mid-altitude coastal mountain region.
• The area experiences Mediterranean Sea influences and is impacted by climate change.
• Significant land cover changes are occurring, with forests expanding at the expense of rangelands.

Purpose of the Study:

• To analyze air temperature trends in Cévennes National Park.
• To investigate the impact of forest expansion on local climate.
• To understand the relationship between climate change, land cover, and temperature variations.

Main Methods:

• Analysis of air temperature data since 1980.
• Monitoring of forest cover changes.
• Application of an intrinsic biophysical mechanism model to assess forest surface temperature compared to grasslands.
• Correlation analysis between temperature trends and weather patterns (e.g., Western Mediterranean Oscillation - WeMO).

Main Results:

• Maximum April-June temperatures increased by up to +0.124 °C/year, uniform across altitudes.
• Minimum temperatures increased by +0.058 °C/year at 500m and +0.089 °C/year at 1500m.
• Forest cover increased by +0.51%/year.
• Forest surfaces were 1.7-3.1 °C cooler than grasslands.
• Forest expansion led to a cooling effect of 0.023 °C/year on maximum air temperatures by decreasing albedo.
• Spring warming trends correlated with negative Western Mediterranean Oscillation phases.

Conclusions:

• Forest expansion in Cévennes National Park has a cooling effect on maximum air temperatures, partially mitigating regional warming.
• Land cover change, specifically afforestation, plays a significant role in modulating local climate responses to broader climate change.
• Atmospheric humidity and radiative forcing, influenced by large-scale weather patterns, are key drivers of temperature rise in the region.