Evaluation of an urban canopy model in a tropical city: the role of tree evapotranspiration

Abstract

A single layer urban canopy model (SLUCM) with enhanced hydrologic processes, is evaluated in a tropical city, Singapore. The evaluation was performed using an 11 month offline simulation with the coupled Noah land surface model/SLUCM over a compact low-rise residential area. Various hydrological processes are considered, including anthropogenic latent heat release, and evaporation from impervious urban facets. Results show that the prediction of energy fluxes, in particular latent heat flux, is improved when these processes were included. However, the simulated latent heat flux is still underestimated by ∼40%. Considering Singapore's high green cover ratio, the tree evapotranspiration process is introduced into the model, which significantly improves the simulated latent heat flux. In particular, the systematic error of the model is greatly reduced, and becomes lower than the unsystematic error in some seasons. The effect of tree evapotranspiration on the urban surface energy balance is further demonstrated during an unusual dry spell. The present study demonstrates that even at sites with relatively low (11%) tree coverage, ignoring evapotranspiration from trees may cause serious underestimation of the latent heat flux and atmospheric humidity. The improved model is also transferable to other tropical or temperate regions to study the impact of tree evapotranspiration on urban climate.

Application of MORUSES single‐layer urban canopy model in a tropical city: Results from Singapore

“…(). Daytime Q H was also overestimated in most previous studies (Demuzere et al ., ; Harshan et al ., ; Liu et al ., ) and a similar delay is found in Liu et al . (2017).…”

“…The present coupled result is opposite to what has been found in past Singapore studies (coupled and uncoupled), where Q E is always underestimated. All of the studies considering the same period (Demuzere et al ., ; Harshan et al ., Liu et al ., ) are performed in uncoupled mode.…”

“…González et al ., ; Comarazamy et al ., ; Murphy et al ., ) or specifically for Singapore (Li et al ., ; ; Demuzere et al ., ; Harshan et al ., ; Liu et al ., ). Some of the studies done in Singapore were performed in uncoupled mode (Demuzere et al ., ; Harshan et al ., ; Liu et al ., ), not allowing for the assessment of potential impacts of the city feedback on the atmosphere above. Climate change impacts are understudied in the Tropics where the growth of cities is largest (Seto et al ., ) hence the importance and need to better understand urban‐induced changes to the local and regional atmosphere.…”

“…Masson et al, 2002;Lemonsu et al, 2004;Bohnenstengel et al, 2011;Salamanca et al, 2011a;2011b), only a few have been carried out for (sub)tropical cities (e.g. González et al, 2005;Comarazamy et al, 2010;Murphy et al, 2011) or specifically for Singapore (Li et al, 2013;Demuzere et al, 2017;Liu et al, 2017). Some of the studies done in Singapore were performed in uncoupled mode Liu et al, 2017), not allowing for the assessment of potential impacts of the city feedback on the atmosphere above.…”

Modeling the Impacts of Urbanization on Summer Thermal Comfort: The Role of Urban Land Use and Anthropogenic Heat

“…Third, the urban hydrological processes, such as the anthropogenic latent heat release and urban oasis and tree evapotranspiration effects, are not well captured in the WRF/UCM used here, which can affect the estimation of the urbanization effect on RH and heat stress. Future studies are needed to conform our findings using models with more realistic representations of the urban hydrological processes (e.g., Hansen et al, 2013;Liu et al, 2017;Yang et al, 2015). Finally, in this study, WRF is configured with a single high-resolution (i.e., 3 km) domain forced by a reanalysis product with a much coarser resolution (i.e., 1°).…”