Abstract
Urban Land Surface Models (ULSMs) simulate energy and water exchanges
between the urban surface and atmosphere. When part of numerical weather
prediction, ULSMs provide a lower boundary for the atmosphere and
improve the applicability of model results in the urban environment
compared with non-urban land surface models. However, earlier systematic
ULSM comparison projects assessed the energy balance but ignored the
water balance which is coupled to the energy balance. Here, we analyze
the water balance representation in 19 ULSMs participating in the
Urban-PLUMBER project using results for 20 sites spread across a range
of climates and urban form characteristics. As observations for most
water fluxes are unavailable, we examine the water balance closure, flux
timing, and magnitude with a score derived from seven indicators. We
find that the water budget is only closed in 57% of the model-site
combinations assuming closure when annual total incoming fluxes
(precipitation and irrigation) fluxes are within 3% of the outgoing
(all other) fluxes. Results show the timing is better captured than
magnitude. No ULSM has passed all good water balance indicators for any
site. Our results indicate models could be improved by explicitly
verifying water balance closure and revising runoff parameterizations.
By expanding ULSM evaluation to the water balance and related to latent
heat flux performance, we demonstrate the benefits of evaluating
processes with direct feedback mechanisms to the processes of interest.