When comparing modelled urban heat sensible heat flux with observation

[Yuan Sun]

Hi all,

I attempt to verify urban modelling performance by comparing single-point model outputs with observation. I compare the FSH_U from CLMU (light line) with Qh from heat flux towers (dark line).

However, the model underestimates sensible heat flux in winter in several sites and overestimates sensible heat flux in summer in other sites. I tried to understand the cause of seasonal variations in modelling sensible heat.

Is it correct to compare directly FSH_U to Qh, or Shall I use the sum of FSH_U + URBAN_HEAT + WASTEHEAT when comparing with observed Qh, though the current gap between modelled sensible heat and observation from my simulation is far larger than sensible heat from the building?

Will urban heating and air conditioning be a potential cause of sensible heat flux uncertainties? For example, if I set a small T_BUILD_MIN, will it lead to less FSH_U and URBAN_HEAT in winter? If I set a larger T_BUILD_MAX, will it lead to more FSH_U in summer?

I attached the results from several sites. Thanks for any comments.

Best,
Yuan

 

[oleson]

Yes, compare FSH_U to Qh. Yes, HAC can be a potential cause of sensible heat flux uncertainties. I would expect a lower T_BUILD_MIN to result in less heating and lower sensible heat flux in winter. In summer, it's difficult to say. A higher T_BUILD_MAX would result in less air conditioning and warmer interior building temperature which may translate into higher sensible heat flux. But less wasteheat will be dumped into the canyon which would likely reduce sensible heat flux.

 

[Yuan Sun]

Yes, compare FSH_U to Qh. Yes, HAC can be a potential cause of sensible heat flux uncertainties. I would expect a lower T_BUILD_MIN to result in less heating and lower sensible heat flux in winter. In summer, it's difficult to say. A higher T_BUILD_MAX would result in less air conditioning and warmer interior building temperature which may translate into higher sensible heat flux. But less wasteheat will be dumped into the canyon which would likely reduce sensible heat flux.

Hi Keith,

Thanks for your guidance. I would tune my indoor temperature parameter input if necessary.

Best,
Yuan

 

[Yuan Sun]

Yes, compare FSH_U to Qh. Yes, HAC can be a potential cause of sensible heat flux uncertainties. I would expect a lower T_BUILD_MIN to result in less heating and lower sensible heat flux in winter. In summer, it's difficult to say. A higher T_BUILD_MAX would result in less air conditioning and warmer interior building temperature which may translate into higher sensible heat flux. But less wasteheat will be dumped into the canyon which would likely reduce sensible heat flux.

Hi Keith,

I am a little bit confused as you mentioned WASTEHEAT. When I think more about the overestimated FSH_U in summer in several sites, the WASTEHEAT is split from FSH_U in the urban surface energy budget equation, right? Despite the higher indoor temperature might also lead to less WASTEHEAT, WASTEHEAT is not incorporated in FSH_U. So when comparing FSH_U to Qh, it seems no need to consider WASTEHEAT. Could I explain higher indoor temperature in summer might lead to higher FSH_U?

I am not sure if I express my understanding clearly or not. Looking forward to your comments

Best,
Yuan

 

[oleson]

What I meant by wasteheat is that less/more heat dumped into the urban canyon can decrease/increase air temperature in the canyon. Since the sensible heat flux is computed from the difference between canyon air temperature and forcing temperature, this can decrease/increase sensible heat flux.

 

[Yuan Sun]

Hi Keith,

I see. Thanks for your helpful comments.

Best,
Yuan