Development and evaluation of a new fully-coupled urban atmospheric-hydrological model
Abstract
Urban features strongly perturb the energy-water cycle in cities. Additionally, the water table can influence atmospheric-hydrological processes and coupling in places with shallow groundwater. To investigate the impact of these features on the urban energy-water cycle, we built a fully-coupled urban atmosphere-land surface-subsurface model, WRF-PUCM-ParFlow, by coupling two existing models (WRF-ParFlow and WRF-PUCM, where PUCM is the Princeton Urban Canopy Model). ParFlow represents the complex urban terrestrial hydrology, while PUCM represents heterogeneity of energy and water fluxes and processes in cities. We compared outputs of WRF-PUCM-ParFlow to WRF-PUCM applied to a small highly-urbanized (~50% impervious cover) watershed in Baltimore, MD, USA. The domain is 116.6 km2, simulated with a horizontal resolution of 90 m x 90 m and 120 grid cells. WRF was used in the large-eddy simulation (LES) mode. The period of the simulations was 96 hours from July 19, 2008 to July 23, 2008. This started with a dry down period for 40 hours followed by two rain events. The two models started from the same initial conditions. For the first 40 hours of the simulation, the two models showed similar performance, where area-averaged time-series of soil moisture (SM) and land surface temperature (LST) were almost identical. At hour 40 of the simulation, a precipitation event started, after which the spatial distribution of soil moisture of the two models started to diverge. Although the precipitation amount for that event was identical in both simulations, the WRF-PUCM model showed higher rates of infiltration compared to WRF-PUCM-ParFlow, due to the implementation of different terrestrial hydrology in the two models. The increase in the area-averaged SM in the WRF-PUCM simulation was four times larger than in the WRF-PUCM-ParFlow simulation. The difference between soil moisture distribution led to differences in other microclimatic variables such as LST. At the end of the simulation, near hour 90, the area-averaged difference in LST between the two models reached almost 2 degrees C. These results suggest that the physically-based representation of terrestrial hydrology in ParFlow results in significant differences in the forecasts of the two models, and needs to be captured for accurate urban weather and climate simulations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H44E..03T
- Keywords:
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- 1803 Anthropogenic effects;
- HYDROLOGY;
- 1833 Hydroclimatology;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY;
- 1878 Water/energy interactions;
- HYDROLOGY