Abstract:
As part of an interdisciplinary research programme, the spatial and temporal variability of precipitation in southern Ecuador
has been investigated since January 2002. The study site is located at the northern margin of the Podocarpus National Park in
the vicinity of Loja, about 500 km south of Quito, at altitudes ranging from 1800 to 3200 m.a.s.l. Due to its low density, the
conventional rainfall station network fails to register the highly variable spatial distribution of rain, whereas contributions by
fog are not accounted at all. Hence, for the first time in a tropical montane forest setting, a weather radar was used, covering a
radius of 60 km and reaching from the Amazon Basin to the coastal plains of the region. Furthermore, a network of sampling
stations supplies data about the altitudinal gradient of fog and rainwater inputs. The precipitation distribution in the study
area proves to be far more variable than previously thought and is strongly coupled to the orographic characteristics and
the special topographical setting of the landscape. Maxima in precipitation occur especially in the eastern parts of the radar
range on slopes exposed to advected moisture from the Amazon Basin, whereas the highest crests of the Andes receive less
precipitation. The study area has two cloud condensation levels, occurring at 1500?2000 and 2500?3500 m.a.s.l., respectively.
At 1800?2000 m.a.s.l., fog is estimated to contribute an additional input of 5% of conventionally measured rainfall, increasing
to about 35% at the highest measurement station (3200 m.a.s.l.). In contrast to some other tropical mountains, there seems to be
no maximum zone of water input, although the gradient remains positive up to the highest altitudes. The unusual precipitation
distribution is thought to reflect the contrasting climatological influences operating in the study area.
