Rainforest Weather: Perpetual Warmth, Rain, and Humidity

The Engine of Biodiversity

Tropical rainforests (African Congo, Amazon, Southeast Asia) exhibit remarkably stable, extreme climates that drive their unparalleled productivity and diversity.

1. Temperature: Constant Warmth

• Range: 25–28°C (77–82°F) year-round.
• Diurnal > Seasonal: Day-night variation (5–10°C) exceeds seasonal variation.
• No Frost: Allows continuous growth; no dormancy.

2. Rainfall: Abundant & Frequent

• Annual: 1,500–4,000+ mm (60–160+ in).
• Distribution: No true dry month; <100 mm/month even in "drier" periods.
• Type: Primarily convectional—intense afternoon thunderstorms from rapid heating.

3. Humidity: Near Saturation

• Relative Humidity: 80–95% (often 100% at night).
• Vapor Pressure: High absolute moisture content.
• Effect: Reduces transpiration stress; promotes epiphytes, fungi, decomposition.

4. Cloud Cover & Light

• Persistent cloud layers (especially at mid-levels).
• Canopy intercepts 98% of light; forest floor is dim (1–2% PAR).

5. Microclimates & Variability

• Vertical Stratification: Canopy (hotter, drier, windier) vs. understory (cooler, humid, still).
• Elevation: Montane/cloud forests cooler, wetter, mistier.
• El Niño/La Niña: Causes droughts/floods (e.g., 1997–98, 2015–16 Amazon droughts).

Climate Change Threat

Even small temperature rises increase vapor pressure deficit, stressing trees. Altered rainfall patterns risk "savannization" of southern Amazon. The stability that defines rainforests is their greatest vulnerability.