18
Fig. 1.7 Observed (open
squares) and modelled
(filled squares) urban heat
island intensity (°C) in
Budapest for 1961–1970
(solid lines) and 1991–
2000 (dashed lines)
underestimation can be seen. In the concordantly overheated months, the results of
Kitaibel Street are better, while in the rest of the year (except for April) this statement is valid only for the earlier period. Since ECOCLIMAP database provides
information about recent surface characteristics, the reduced overestimation in
Pestszentlőrinc in 1991–2000 compared to the results of 1961–1970 might be
caused partly by the more realistic coverage description. (However, the fact that the
improvements cannot be detected in every months indicates the key role of different
atmospheric forcings in the two periods, especially in summer.)
In contrast with the temperature measurements, urban heat island cannot be
noticed in any periods of the year (Fig. 1.7), which means that the inner point is
colder than the outer one in the model. This already appears in the ALADIN-Climate
results, and SURFEX cannot improve this, especially because the two points are
characterised with the same cover type in the ECOCLIMAP. Moreover, Kitaibel
Street locates on higher elevation than Pestszentlőrinc, and the neighbouring of the
Buda Hills to the inner site might cause too strong cooling in ALADIN-Climate
compared to the observations (recall that SURFEX does not simulate interactions
between the neighbouring grid cells).
In the two reference points the results does not indicate good performance, but if
a larger area is taken, SURFEX captures the daily cycle of UHI (Fig. 1.8). In daytime the air temperature of the city centre does not differ from the reference point in
the suburban area; however after dusk (in winter already at 18:00, in summer at
21:00 UTC) UHI appears and its maximum intensity can be seen 5–6 h after sunset.
The physical reason is that energy supply by solar radiation ends after sunset and
upward longwave radiation is much more effective over natural surfaces than in the
densely built-in urban area due to the smaller heat capacity of soil and the trapping
of radiation in urban canyons (Basically the same conclusions were drawn for
1991–2000).
J. Fallmann et al.
Fig. 1.7 Observed (open
squares) and modelled
(filled squares) urban heat
island intensity (°C) in
Budapest for 1961–1970
(solid lines) and 1991–
2000 (dashed lines)
underestimation can be seen. In the concordantly overheated months, the results of
Kitaibel Street are better, while in the rest of the year (except for April) this statement is valid only for the earlier period. Since ECOCLIMAP database provides
information about recent surface characteristics, the reduced overestimation in
Pestszentlőrinc in 1991–2000 compared to the results of 1961–1970 might be
caused partly by the more realistic coverage description. (However, the fact that the
improvements cannot be detected in every months indicates the key role of different
atmospheric forcings in the two periods, especially in summer.)
In contrast with the temperature measurements, urban heat island cannot be
noticed in any periods of the year (Fig. 1.7), which means that the inner point is
colder than the outer one in the model. This already appears in the ALADIN-Climate
results, and SURFEX cannot improve this, especially because the two points are
characterised with the same cover type in the ECOCLIMAP. Moreover, Kitaibel
Street locates on higher elevation than Pestszentlőrinc, and the neighbouring of the
Buda Hills to the inner site might cause too strong cooling in ALADIN-Climate
compared to the observations (recall that SURFEX does not simulate interactions
between the neighbouring grid cells).
In the two reference points the results does not indicate good performance, but if
a larger area is taken, SURFEX captures the daily cycle of UHI (Fig. 1.8). In daytime the air temperature of the city centre does not differ from the reference point in
the suburban area; however after dusk (in winter already at 18:00, in summer at
21:00 UTC) UHI appears and its maximum intensity can be seen 5–6 h after sunset.
The physical reason is that energy supply by solar radiation ends after sunset and
upward longwave radiation is much more effective over natural surfaces than in the
densely built-in urban area due to the smaller heat capacity of soil and the trapping
of radiation in urban canyons (Basically the same conclusions were drawn for
1991–2000).
J. Fallmann et al.