Tier 2 Dewpoint Depression Change

1 figure · 1990–2014 → 2040–2049

Synthesis

Mid-century projections indicate widespread continental drying and increased atmospheric thirst over the Amazon and Mediterranean, contrasted by moisture intensification over African and Asian monsoon regions.
The diagnostic compares projected changes in dewpoint depression (DPD) for the mid-century (2040–2049) relative to the historical period (1990–2014) under the SSP3-7.0 scenario, revealing a stark land-sea contrast driven by differential warming rates. Widespread continental drying is the dominant signal, with land masses generally exhibiting positive DPD anomalies that indicate a reduction in relative humidity; this is physically consistent with the land-ocean warming contrast, where continental temperatures rise faster than the specific humidity supplied by oceanic advection can compensate. The strongest drying signals (>1.5 K increase in DPD) are concentrated in the Amazon Basin, Southern Africa, the Mediterranean, and Western North America, suggesting significantly enhanced aridity and potential vegetation stress in these regions. Conversely, distinct regions of wetting (decreased DPD) are observed over the Sahel, the Indian subcontinent, and East Africa, consistent with the thermodynamic intensification of monsoon circulation and enhanced moisture convergence. Oceanic regions remain largely stable or show slight moistening (anomalies of 0 to -0.5 K). The comparison between IFS-FESOM and IFS-NEMO shows exceptional agreement in spatial structure and magnitude, indicating that the atmospheric physics of the IFS model dominates the surface hydroclimate response, with the choice of unstructured versus structured ocean grids having negligible impact on the broad patterns of terrestrial atmospheric moisture demand.

Related diagnostics

relative_humidity 2m_temperature precipitation soil_moisture

Dewpoint Depression Change

Dewpoint Depression Change
Variables avg_2t, avg_2d
Models ifs-fesom, ifs-nemo
Units K
Baseline 1990-2014
Future 2040-2049
Method ΔDPD = (T_fut − Td_fut) − (T_hist − Td_hist).

Summary high

The figure illustrates the projected change in dewpoint depression (DPD) between 1990–2014 and 2040–2049 under SSP3-7.0, revealing a dominant pattern of continental drying (increasing DPD) contrasted with stability or slight moistening over oceans and specific monsoon regions.

Key Findings

  • Widespread increases in DPD (>1.5 K) are observed over the Amazon Basin, Southern Africa, the Mediterranean, and Western North America, indicating a reduction in relative humidity.
  • Prominent decreases in DPD (wetting) occur over the Sahel, the Indian subcontinent, and parts of East Africa, suggesting intensified monsoon moisture transport.
  • Oceanic regions predominantly show slight decreases in DPD (0 to -0.5 K), implying that near-surface air over oceans maintains or slightly increases relative humidity.

Spatial Patterns

A stark land-sea contrast exists where land masses generally exhibit positive anomalies (browning) and oceans exhibit weak negative anomalies (teal). Notable exceptions on land include the 'wetting' bands across the Sahel and South Asia. The Amazon and Southern Africa show the most intense drying signals.

Model Agreement

There is exceptionally high agreement between IFS-FESOM and IFS-NEMO regarding spatial structure and magnitude. This suggests that the atmospheric component (IFS) dominates the surface hydroclimate response, with the choice of ocean model (unstructured FESOM vs. structured NEMO) having minimal impact on the broad terrestrial patterns of mid-century dewpoint depression change.

Physical Interpretation

The pervasive land drying is driven by the land-ocean warming contrast: land temperatures ($T$) rise faster than oceanic moisture sources allow the dewpoint ($T_d$) to increase, widening the depression ($T-T_d$) and lowering relative humidity. In contrast, the negative anomalies over India and the Sahel are consistent with thermodynamic intensification of monsoon circulation, where increased moisture convergence raises $T_d$ faster than $T$.

Caveats

  • Both panels utilize the same atmospheric model (IFS), likely underrepresenting structural uncertainty in atmospheric physics compared to a multi-model ensemble.
  • The 2040–2049 timeframe represents a transient state; patterns, particularly in the Amazon, could intensify further by 2100.