East Asia and Western Pacific METEOROLOGY AND CLIMATE

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an effort to minimize the impact of this building activity. In
contrast the wind measured at the 900 hPa level in the free atmosphere
did not change appreciably during the same period (Peterson, 8))
indicating this feature as the likely source of the reduction in
surface windspeed.
In addition, this increase in building height would result in
the presence of warmer buildings occupying a larger solid angle
relative to the cooler sky. Such a reduction in sky view factor would
reduce the loss of heat by longwave radiation from the surface (factor
2) thereby tending to contribute to elevated night-time minimum
temperatures. Finally, during this period factor 5 probably assumed
increasing importance with greater building volume, increasing
population, more human activity and traffic all contributing to the
anthropogenic heat added to the urban canopy. Again, the trend of
more rapidly increasing minima than maxima during this period is
consistent with this scenario.
Lastly, in the 1970 T s and 80 f s the increase both in built-up
area and building volume has nearly ceased as the area has become
almost totally built-up to the maximum permitted by zoning regulations.
However, the increase in population density, traffic volume and the
use of air conditioning has meant that factor 5 probably has assumed a
more dominant role than heretofore. While a continuing increase in
night-time minimum temperatures is consistent with this effect it is
more difficult to explain the steady decline in daytime maxima during
this phase. The explanation may, however, be linked to the fact that
the Royal Observatory is still surrounded in its immediate area by
actively transpiring vegetation. Additional available energy may
enhance this transpiration thus causing a cooling effect not only offsetting
the tendency to further increase in daytime maxima but even
reversing it. In effect the postulation is that factor 6 may not
apply in this situation.
While all that has been postulated so far must be considered
as derived from observed associations it appears to be internally