Tier 1 Freshwater Flux (P−E)
Synthesis
Related diagnostics
Evaporation Change
| Variables | avg_tprate, avg_ie |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | kg/m2/s |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean of avg_ie. |
Summary high
The figure illustrates the projected change in surface evaporation rates between the mid-century (2040–2049, SSP3-7.0) and the historical baseline (1990–2014) for two high-resolution coupled models, IFS-FESOM and IFS-NEMO. Both models exhibit robust, structurally similar global patterns characterized by enhanced oceanic evaporation in western boundary currents and high latitudes, contrasted by evaporation reductions in the subpolar North Atlantic and distinct semi-arid land regions.
Key Findings
- A prominent dipole exists in the North Atlantic: enhanced evaporation along the Gulf Stream extension contrasts with a marked reduction (brown) in the subpolar gyre/North Atlantic Current region.
- Significant reductions in evaporation are evident over key land regions, specifically the Amazon Basin, the Mediterranean, Southern Africa, and Central America, suggesting moisture-limited regimes.
- High-latitude oceans (Arctic and Antarctic margins) show strong increases in evaporation (teal), spatially coincident with projected sea-ice retreat.
- The Southern Ocean displays a zonal banding structure with alternating increases and decreases, likely linked to shifts in the westerly wind belt.
Spatial Patterns
The ocean shows a thermodynamic increase in evaporation in the subtropics and western boundary currents (e.g., Kuroshio, Gulf Stream), driven by warmer SSTs. In contrast, the 'warming hole' region in the North Atlantic shows suppressed evaporation. Over land, the pattern is bimodal: northern high-latitude land masses (Eurasia, North America) show increased evaporation (energy-limited release), while subtropical dry zones (Mediterranean, Amazon) show decreases (water-limited restriction).
Model Agreement
There is exceptionally high structural agreement between IFS-FESOM (unstructured grid) and IFS-NEMO (structured grid), indicating that the atmospheric component (IFS) or fundamental thermodynamic forcing dominates over ocean grid sensitivities. Minor discrepancies exist in the magnitude of signals in the Southern Ocean sea-ice zone and small-scale features in the Indian Ocean.
Physical Interpretation
Oceanic increases are primarily driven by the Clausius-Clapeyron relation (warmer SSTs increase saturation vapor pressure). The North Atlantic reduction is a fingerprint of a weakened AMOC, leading to cooler relative SSTs in the subpolar gyre. High-latitude increases result from sea-ice loss exposing warmer open water to cold air. Land reductions in the Amazon and Mediterranean indicate a transition to soil-moisture-limited regimes where precipitation deficits preclude higher evaporation rates despite increased evaporative demand.
Caveats
- The 10-year averaging period (2040-2049) is relatively short and may allow decadal internal variability (e.g., ENSO, PDO phases) to imprint on the climate change signal.
- Evaporation changes over land cannot be fully interpreted without accompanying precipitation and soil moisture data to distinguish between energy-limited and water-limited drivers.
P−E Change (Freshwater Flux)
| Variables | avg_tprate, avg_ie |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | kg/m2/s |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Δ(P−E) = Δ(avg_tprate) − Δ(avg_ie). |
Summary high
The figure illustrates projected changes in freshwater flux ($P-E$) for the 2040s (SSP3-7.0) relative to the 1990-2014 baseline, exhibiting a robust 'wet-gets-wetter, dry-gets-drier' global pattern. Both IFS-FESOM and IFS-NEMO show intensified moisture convergence in the ITCZ and high latitudes, contrasted with enhanced evaporative dominance in the subtropical gyres.
Key Findings
- Pronounced intensification of freshwater flux (wetting) along the equatorial ITCZ, particularly in the central Pacific and Atlantic Oceans.
- Widespread decreases in $P-E$ (drying) across the subtropical subsidence zones, most notably in the North Atlantic (Azores High), South Atlantic, South Pacific, and the Mediterranean region.
- Consistent high-latitude wetting trend ($>50^{\circ}$N/S) over the Southern Ocean, North Atlantic subpolar gyre, and Arctic, driven by increased poleward moisture transport.
- Strong drying signal over the Amazon basin and Central America, contrasted with wetting over the Asian monsoon region and the Maritime Continent.
Spatial Patterns
The tropical Pacific displays a complex zonal banding structure with a narrow wet core flanked by drying margins, indicative of ITCZ narrowing or intensification. The North Atlantic shows a dipole pattern: drying in the subtropics extending to the Mediterranean and wetting in the subpolar gyre. The Indian Ocean exhibits a dipole-like change, with wetting in the west and drying in the east. Over land, significant drying is observed in the Amazon, southern Africa, and southern Europe, while northern Eurasia and parts of central Africa show wetting.
Model Agreement
Agreement is remarkably high between IFS-FESOM and IFS-NEMO, which is expected as they share the same atmospheric component (IFS). Both capture the fine-scale structure of precipitation filaments and orographic features identically. Minor discrepancies exist in the magnitude of anomalies in the eastern Indian Ocean and subtle textural differences along the Gulf Stream and Kuroshio Extension, likely arising from differences in mesoscale ocean-atmosphere feedback between the FESOM (unstructured) and NEMO (structured) grids.
Physical Interpretation
The patterns are largely driven by the thermodynamic Clausius-Clapeyron response: a warmer atmosphere holds more water vapor (~7%/K), enhancing moisture convergence in climatologically wet convergence zones (ITCZ, storm tracks) and enhancing moisture divergence in dry subsidence regions (subtropics). The poleward expansion of the drying zones is consistent with the projected expansion of the Hadley circulation. The drying over land (e.g., Amazon, Mediterranean) suggests evaporative demand is increasing faster than precipitation supply, or a shift in circulation patterns.
Caveats
- The analysis compares a single future decade (2040-2049) against a historical baseline; internal decadal variability (e.g., ENSO, PDO phases) may overlay the forced climate signal.
- Both models use the same atmospheric physics (IFS); thus, the high agreement reflects the robustness of the IFS response rather than a multi-model consensus.
Precipitation Change
| Variables | avg_tprate, avg_ie |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | kg/m2/s |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean of avg_tprate. |
Summary medium
The figure illustrates the projected change in total precipitation rate (kg/m²/s) between the 2040-2049 period (SSP3-7.0) and the 1990-2014 baseline for two high-resolution coupled models, IFS-FESOM and IFS-NEMO. Both models exhibit robust high-latitude wetting and tropical drying/wetting dipoles, but differ significantly in their tropical Pacific response structures.
Key Findings
- High-latitude amplification: Both models show widespread precipitation increases in the Arctic, Northern Eurasia, and the Southern Ocean.
- Tropical Pacific Divergence: IFS-NEMO displays a strong meridional dipole in the Pacific (drying north of the equator, wetting south), implying a southward ITCZ shift, whereas IFS-FESOM shows equatorial drying flanked by wetting bands.
- Regional Drying Hotspots: Consistent severe drying is observed over the Amazon basin, the Mediterranean region, and Central America in both simulations.
- Asian Monsoon Intensification: Both models project increased precipitation over South Asia and the Indian Ocean, though the spatial extent varies.
Spatial Patterns
The maps display a 'wet-get-wetter' pattern in the extratropics, with teal (positive) anomalies dominating the storm tracks of the North Atlantic and North Pacific. In the tropics, the patterns are dominated by zonal shifts. The Amazon shows a strong brown (drying) signal (> -5e-6 kg/m²/s). The Indian Ocean shows a dipole-like wetting pattern, particularly strong in the western basin. The North Atlantic exhibits a tripole pattern of anomalies, with drying in the subtropics/Mediterranean and wetting at higher latitudes.
Model Agreement
The models agree on the thermodynamic signal (high-latitude wetting) and land-surface driven drying over the Amazon and Mediterranean. Disagreement is most pronounced in the Tropical Pacific, where IFS-NEMO predicts a coherent southward displacement of the rain belt, while IFS-FESOM predicts a narrowing or intensification of the equatorial cold tongue drying with off-equatorial wetting. This suggests differences in the coupled ocean response (SST patterns) between the FESOM and NEMO ocean components.
Physical Interpretation
High-latitude wetting is driven by the Clausius-Clapeyron relation (warmer air holding more moisture). The Amazon drying likely involves land-atmosphere feedbacks and stability increases. The tropical patterns reflect changes in the Hadley and Walker circulations; the IFS-NEMO Pacific pattern specifically suggests a response to meridional SST gradients potentially linked to an Interdecadal Pacific Oscillation-like phase or a structural ITCZ shift.
Caveats
- The 10-year future averaging period (2040-2049) is short relative to precipitation variability; decadal internal variability (e.g., ENSO, PDO) likely contaminates the forced climate change signal.
- Differences in ocean grids (unstructured FESOM vs. structured NEMO) may contribute to the divergent tropical SST and precipitation biases.
- No statistical significance masking is applied, so smaller anomalies in mid-latitudes may be noise.