Question on SUEWS sensitivity to vegetation parameters

General
6

Glad to hear the MaxConductance approach is working — and that the magnitude makes physical sense compared to the surface fraction response.

Other parameters worth exploring

For cooling and water use, the most influential parameters in SUEWS tend to be:

  • Surface fractions (which you’ve already tested — this is the dominant lever)
  • MaxConductance (g_{s,\max}) — now confirmed working for you
  • Soil storage capacity (soildepth, soilstorecap) — controls how long the soil can sustain transpiration between rain events, so it shapes the dry-spell response rather than peak cooling
  • Water distribution (waterdist) — governs how rainfall/irrigation runoff is redistributed between surfaces, which affects soil moisture availability
  • Irrigation parameters — if you’re comparing irrigated vs non-irrigated green infrastructure scenarios

On tree height: you’re right that it doesn’t directly affect stomatal conductance or the g_\mathrm{LAI} calculation. It enters SUEWS indirectly through the roughness length (z_{0m}) and displacement height (z_d), which determine the aerodynamic resistance R_A. In the Penman-Monteith equation:

Q_E = \frac{s \cdot Q_{n,e} + \rho c_p \cdot \mathrm{VPD} / R_A}{s + \gamma\left(1 + R_S / R_A\right)}

a lower R_A (from taller roughness elements) increases the VPD-driven term in the numerator and also changes the R_S/R_A balance in the denominator. So taller trees can modestly increase QE, but the effect is secondary compared to g_{s,\max} and surface fractions.

On T2 and cooling efficiency

I’ve seen Fredrik’s separate post about T2 — I’ll reply there with more detail on the physics settings and profile scheme configuration. The short version: T2 sensitivity in SUEWS depends heavily on which RSL (roughness sub-layer) method you’re using (rslmethod) and how the vertical temperature profile is constructed. Your config uses rslmethod: 2, which is the more physically-based option, but there are some important considerations for intra-urban comparisons that I’ll cover in that thread.

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