Thanks for the detailed follow-up and for sharing your files, Janka — that made it much easier to track down what’s going on.
The good news is there’s nothing wrong with your code or setup. The near-zero LAI sensitivity is actually expected behaviour given how SUEWS computes surface conductance. Here’s why.
How LAI enters the conductance calculation
The Jarvis-type surface resistance model computes a LAI factor (g_\mathrm{LAI}) as:
g_\mathrm{LAI} = \sum_{v} \left[ f_v \cdot \frac{\mathrm{LAI}_v}{\mathrm{LAI}_{\max,v}} \cdot g_{s,\max,v} \right]
where f_v is the surface fraction, \mathrm{LAI}_v is the daily LAI, \mathrm{LAI}_{\max,v} is the configured maximum LAI, and g_{s,\max,v} is MaxConductance for each vegetation type v.
The key is the \mathrm{LAI}/\mathrm{LAI}_{\max} ratio. During peak summer, the phenology model grows LAI up to \mathrm{LAI}_{\max} — which you confirmed is happening — so the ratio becomes:
\frac{\mathrm{LAI}_{\max}}{\mathrm{LAI}_{\max}} = 1.0
regardless of what value you set for \mathrm{LAI}_{\max}. The numerator and denominator cancel out.
In other words, \mathrm{LAI}_{\max} in SUEWS doesn’t control how much a tree transpires at full canopy — it controls the timing of the seasonal cycle (when the canopy reaches “fully developed”). The actual magnitude of transpiration at full development is controlled by MaxConductance (g_{s,\max}).
Why surface fractions work but LAImax doesn’t
Surface fractions (f_v) enter the same formula as a direct multiplier with no normalisation, so they scale g_\mathrm{LAI} linearly — exactly what you observed with the 100+ W m⁻² QE response.
What to use instead
For your impact study, if you want to simulate “denser canopy → more transpiration”, vary MaxConductance rather than LAImax. In your config, these are set per vegetation type:
- Evergreen trees:
maxconductance: 1.7 mm s⁻¹
- Deciduous trees:
maxconductance: 3.1 mm s⁻¹
- Grass:
maxconductance: 3.7 mm s⁻¹
Increasing maxconductance for trees will directly increase canopy conductance and hence QE — no normalisation to cancel the signal.
The small residual (~0.01 W m⁻²) you saw comes from transition periods in early summer where the LAI growth trajectory differs slightly between runs, but this vanishes once LAI reaches its configured maximum.
Hope this helps!
