Surface urban energy and water balance scheme – SUEWS
Leena Järvi, Sue Grimmond, Heikki Setälä ja Maija Taka
In urban areas the typically high impervious surface fraction affects
the surface energy and water balances by increasing turbulent heat
emissions to the atmosphere and surface runoff, and by decreasing
evaporation. The energy and water exchanges are not commonly measured
so modeling approaches are needed particularly for urban planning and
mitigation purposes. The Surface Urban Energy and Water Balance Scheme
(SUEWS) is a new model which provides a simple tool to simulate both
balances through the use of commonly measured meteorological variables
and surface cover information. Rates of evaporation-interception for a
single layer with multiple surface types (paved, buildings, coniferous
trees/shrubs, deciduous trees/shrubs, irrigated grass, nonirrigated
grass and water) are calculated. Below each surface type, except water,
there is a single soil layer. At each time step (5 min to 1 h) the
moisture state of each surface and soil are calculated. Horizontal
water movements at the surface and in the soil are incorporated. In
order to minimize the number of required input variables, the model
contains several sub-models for e.g. net all-wave radiation (Q*),
storage heat (ΔQs) and anthropogenic heat flux (QF) and external
irrigation. SUEWS has been tested with three datasets from Vancouver
and two from Los Angeles, where it was found to simulate Q*, QH and QE
well with rmse between 25-47, 30-59 and 20-55 W m-2, respectively. In
addition, the model was able to simulate surface wetness and soil
moisture changes. It has also been tested to simulate surface runoff
from two catchments in Helsinki with varying surface cover in October –
November 2010. For both catchments SUEWS simulated the behavior of
measured runoff well but overestimates runoff values slightly when
applied in an uncalibrated manner with the default model parameters.