Tier 2 Precipitation Concentration Index

1 figure · 1990–2014 → 2040–2049

Synthesis

Mid-century projections indicate a robust global increase in precipitation concentration, specifically intensifying seasonality within the Sahelian and Asian monsoon systems and narrowing the Intertropical Convergence Zone.
Projected hydroclimatic changes for the mid-century (2040–2049) under SSP3-7.0 reveal a widespread restructuring of temporal precipitation distribution, characterized by a dominant global trend toward increased Precipitation Concentration Index (PCI). Both IFS-FESOM and IFS-NEMO simulations indicate that precipitation is becoming increasingly clustered in time, consistent with Clausius-Clapeyron scaling where atmospheric warming drives more intense, short-duration events at the expense of moderate, distributed rainfall. This trend effectively sharpens the seasonality of global hydroclimate, particularly within established wet zones, supporting the 'wet-get-wetter' thermodynamic paradigm. Spatially, the intensification of rainfall concentration is most pronounced across the major monsoon systems and the Intertropical Convergence Zone (ITCZ). The Sahel and West African Monsoon region exhibit robust PCI increases (often $\Delta$PCI > 0.6), signaling a shift toward hyper-seasonal or increasingly episodic rainfall regimes. Similar patterns of contraction and intensification appear in the South Asian monsoon and the Australian interior. While the shared atmospheric physics of the IFS models result in strong large-scale agreement, regional discrepancies emerge over the Arabian Peninsula and Eastern Pacific, likely reflecting sensitivity to ocean boundary layer distincts between the FESOM and NEMO couplings.

Related diagnostics

seasonal_cycle_precip extreme_precipitation_indices monsoon_dynamics

Precipitation Concentration Index Change

Precipitation Concentration Index Change
Variables avg_tprate
Models ifs-fesom, ifs-nemo
Units kg/m2/s
Baseline 1990-2014
Future 2040-2049
Method PCI = 12 × Σ(P_i²) / (ΣP_i)² from climatological monthly means. PCI=1 = uniform; PCI>1 = concentrated.

Summary high

The figure illustrates the projected mid-century (2040-2049) change in Precipitation Concentration Index (PCI) under SSP3-7.0 relative to 1990-2014, revealing a dominant global trend towards increased precipitation seasonality and concentration within existing wet seasons.

Key Findings

  • A robust increase in PCI (values > 0.6) is observed across the Sahel and Southern Sahara, indicating a sharp intensification of rainfall concentration in the West African Monsoon region.
  • Major global convergence zones (ITCZ in the Atlantic and Pacific, SPCZ) show increased concentration (teal bands), suggesting a narrowing or intensifying of seasonal precipitation bands.
  • The Australian interior and the South Asian monsoon region display significant increases in rainfall concentration.
  • Decreases in concentration (brown areas) are sparse, appearing patchily in the subtropical Atlantic and specific coastal zones (e.g., Peru/Chile margin in IFS-FESOM).

Spatial Patterns

The spatial distribution of positive $\Delta$PCI strongly correlates with Earth's major monsoon systems and the Intertropical Convergence Zone. The signal is strongest in the Sahel, Arabian Peninsula, and the tropical oceans. High-latitude regions generally show weak or neutral changes.

Model Agreement

There is very high structural agreement between IFS-FESOM and IFS-NEMO, likely due to the shared IFS atmospheric physics. However, IFS-NEMO predicts a much more coherent and intense increase in concentration over the Arabian Peninsula compared to the mixed signal in IFS-FESOM. Subtle differences also appear in the Eastern Pacific upwelling regions, reflecting differences in ocean boundary layer resolution/physics.

Physical Interpretation

The widespread increase in PCI aligns with the 'wet-get-wetter' paradigm and Clausius-Clapeyron scaling, where a warmer atmosphere supports more intense precipitation events during the active season. In monsoon regions (Sahel, India), this suggests a regime shift towards more intense but potentially temporally confined wet seasons. In arid regions (Sahara/Arabia), high positive $\Delta$PCI likely indicates that already sporadic rainfall events are becoming even more episodic.

Caveats

  • PCI changes do not imply total precipitation changes; a drying region can have increased PCI if the remaining rain falls in a shorter window.
  • The 10-year future window (2040-2049) is relatively short for precipitation climatology, implying some patterns may still contain internal variability noise.
  • The visual analysis relies on only two of the three mentioned models (ICON is absent).