Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 31
7 CLIMATE
7.1 Theoretical Considerations
Large water bodies influence the climate of their surroundings, especially temperature
and humidity. The most noticeable effects are a general cooling in summer, a warming
in winter, and a reduction of the daily and seasonal temperature variation. This effect
can be clearly seen when the climate of a place on the seashore, with maritime climate,
is compared to the one of a place far away from sea influence, with a continental climate
type. Direct measurements have documented this effect. So it has been demonstrated
that for instance a small island in the Finnish Bay exhibited a January temperature that
was 1.3°C higher than that of a station in the nearby land some distance away from the
coast, while the average May temperature was 2.5°C lower. Similar, although smaller
effects have been demonstrated in the vicinity of two lakes (Lake Peipus, Lake
Chelkap), although in these cases the differences were smaller, reaching only +0.3° in
winter, -0.7° and -1.8°, resp., in summer (Alissow et al., 1956). This is also illustrated
for Lake Aral in Figure 7-1.
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7.00 h 13.00 h 21.00 h
Figure 7-1: Daily temperature variations as influenced by a lake
Measurements from Lake Aral, August 1902. The daily amplitude of water temperature is
merely 0.6°, of the air above the water 1.5°, at the shore 6.9° and in greater distance from
the lake 9°C (Alissow et al., 1956).
This is mainly due to the fact that the water is able to store a considerable amount of
heat, and that it reacts very slowly to changing temperatures. While on land the
temperature (soil and air layers close to it) can exhibit large daily fluctuations, this is not
the case for water. In Irkutsk, the daily variation in summer is 13.5 to 21.7°C, in winter
5.7 to 14.5°C (air 2 m above ground), the soil surface variation is even greater (29.8° in
summer, 6.2° in winter; measurements for a day with rather low air temperature
variation). It will be noted that Irkutsk is exhibiting a continental climate in spite of the
proximity of Lake Baikal, which is one of the largest inland water bodies of the world.
The biggest daily variations in air and soil temperature are recorded from deserts, which
Water
Air
Shore
Inland