Hydrology
Nile flood peaks may jump this century
Open access · cc by · source: Europe PMC
A basin-wide hydrology model driven by 30 CMIP6 climates projects much larger 50- and 200-year Nile floods at Dongola by 2100.
Study at a glance
- Design
- Computational / modelling — SWAT+ Nile hydrology forced by bias-corrected CMIP6 members under SSP2-4.5 and SSP5-8.5
- N
- N=30 · 30 CMIP6 climates (high/median/low members per SSP run through SWAT+)
- Population
- Nile basin streamflow regimes at Dongola under 21st-century climate scenarios
- Outcome
- Projected increases in 50- and 200-year flood peaks by 2100
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Historical 50- and 200-year peaks are 13,400 and 14,900 m³/s. Median SSP2-4.5 raises them to 21,800 and 24,100 m³/s; SSP5-8.5 exceeds 24,700 and 27,400 m³/s. Extreme streamflow intensity rises 49–63% (SSP2-4.5) and 73–85% (SSP5-8.5). A historical 100-year flood (~14,200 m³/s) occurs about every 4 years (SSP2-4.5) or 2.75 years (SSP5-8.5). Mean AMS rain rises ~29% and ~41%.
Methodology
The authors calibrated SWAT+ (34 subbasins, 234 HRUs) to 1984–1997 gauges, bias-corrected NEX-GDDP CMIP6 rain with QQM, then ran high/median/low members of SSP2-4.5 and SSP5-8.5 through 2100 and fitted log-Pearson III flood peaks.
Limitations
SWAT+ was calibrated on a short 1984–1997 window and does not fully resolve GERD operations. CMIP6 still disagrees on the sign of mean Nile rain. Extreme-value fits have wide 5th–95th percentile bands. Lake Nasser operations can still divert floods.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
NEX-GDDP CMIP6 rain, quantile-mapped and fed to SWAT+, turns a historical 50- and 200-year Nile peak of 13,400 and 14,900 m³/s into 21,800 and 24,100 m³/s (median SSP2-4.5) or >24,700 and >27,400 m³/s (SSP5-8.5). Extreme streamflow intensity rises 49–63% and 73–85%; a historical 100-year flood (~14,200 m³/s) occurs about every 4 years or 2.75 years. Mean AMS rain rises ~29% and ~41%. CMIP6 still disagrees on the sign of mean Nile rain.
Evidence for the claim as stated.
CMIP can match one budget and miss another. Steric TSLS (1.5±0.2) sits on observations (1.4±0.5), yet historical all-but-glacier sea-level sensitivity is ~30% above the models and Antarctic dynamics are observed, not modelled. Downstream, QQM-corrected NEX-GDDP members intensify Nile flood peaks while the same CMIP6 generation still disagrees on the sign of mean Nile rain. Agreement of a multimodel mean on ETCCDI sensitivity does not license treating every CMIP-forced hydrology run as an observation.
Evidence for the claim as stated.
NEX-GDDP already downscales 30 CMIP6 models to 0.25°; an extra QQM step against CHIRPS, then SWAT+ (34 subbasins, 234 HRUs), raises Nile 50- and 200-year peaks from 13,400 and 14,900 m³/s to 21,800 and 24,100 m³/s (median SSP2-4.5) or >24,700 and >27,400 m³/s (SSP5-8.5). A historical 100-year flood (~14,200 m³/s) occurs about every 4 or 2.75 years. CMIP6 still disagrees on the sign of mean Nile rain; SWAT+ was calibrated on 1984–1997 gauges.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
CMIP can match one budget and miss another. Steric TSLS (1.5±0.2) sits on observations (1.4±0.5), yet historical all-but-glacier sea-level sensitivity is ~30% above the models and Antarctic dynamics are observed, not modelled. Downstream, QQM-corrected NEX-GDDP members intensify Nile flood peaks while the same CMIP6 generation still disagrees on the sign of mean Nile rain. Agreement of a multimodel mean on ETCCDI sensitivity does not license treating every CMIP-forced hydrology run as an observation.
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