Flux observations over an urban center in Sakai

PI. Masahito UEYAMA

Research background
To accurately estimate global energy, water and carbon exchange, long-term monitoring of those fluxes has been conducted at many terrestrial ecosystems. However, it is still uncertain in the exchange processes in urban landscape due to lack of continuous measurement. In this study, we have conducted the long-term observations of those fluxes in an urban center, to evaluate 1) diurnal, seasonal, and interannual variation of the fluxes, and 2) important processes related to the fluxes.

Field observations
The measurements were conducted at a city center of Sakai (34o34’25’’N, 135o28’80’’E), where the area is densely built-up; an industrial and commercial center with heavy traffic since winter in 2008. The measurement height is above the blending height, 112 m above ground. Sakai is a second biggest city in Osaka, and a city designated by ordinance. The population exceeds 800,000.

Environmental Variables Method Site
Momentum, sensible heat, and latent heat fluxes Eddy covariance  


CO2 flux Eddy covariance SAC, OPU, IZM
air temperature and humidity Ventilated sensors SAC, OPU, IZM
solar radiation Pyrheliometer SAC, OPU, IZM
Four components of net radiation Component Net Radiometer OPU
surface temperature radiation thermometer SAC, OPU, IZM
rainfall rain gauge OPU
ground heat flux heat plate OPU
evaporation method of weighing OPU
vertical CO2 profile 4 heights SAC

* SAC : Sakai City Office

* OPU : root top of Osaka Prefecture University

* IZM : Oizumi Urban park











Fig. Eddy covariance system over the urban canopy


Observation at the roof top of Osaka Prefecture University
To compare the fluxes between the urban center and a surrounding location, we set up another observation system, including closed path eddy covariance system.









Fig. observations at the roof top of OPU









Fig. observations at Oizumi Urban park.











Fig. An aerial photograph showing our observation point at Sakai Center

Data availability
Observed data can be downloaded from following link.


Ueyama, M., Mitake, Y., Yamaguchi, K. and Hamotani, K., 2011: Micrometeorological measurements of heat, water, and CO2exchanges at an urban landscape in Sakai, Japan. AsiaFlux Newsletter, 32, 9-12.

Ueyama, M., and Ando T. 2016.Diurnal, weekly, seasonal and spatial variabilities in carbon dioxide flux in different urban landscapes in Sakai, Atmos. Chem. Phys., 16, 14727-14740.

Ando T. and Ueyama, M. 2017. Surface energy exchange in a dense urban built-up area based on two-year eddy covariance measurements in Sakai, Japan, Urban Climate, 19, 155-169.