14-04-2014, 12:36 PM
IMPACT OF SECULAR CLIMATE CHANGE ON THE THERMAL STRUCTURE OF A LARGE TEMPERATE CENTRAL EUROPEAN LAKE
LARGE TEMPERATE CENTRAL.pptx (Size: 1.63 MB / Downloads: 10)
Introduction
Data available from the Canadian Experimental Lakes Area from 1970 onwards tend to confirm that lake temperatures are increasing
Whereas monthly mean surface air temperature data sets exist that stretch back two or three centuries without interruption, uninterrupted lake water temperature profile data sets longer than two or three decades are very rare. Where they do exist, such data sets represent a valuable source of information on the immediate physical effects of climate change on lacustrine systems.
Methodology
Standardizing of measurement with respect to depth and time with the more regularly measured meteorological variables
Interpolating at daily intervals using a cubic spline and the interpolated values over each calendar month
Results & Discussions
Secular increase in mean lake temperature is due to a reduction in the heat lost by the lake to the atmosphere during the night.
Of the five heat exchange processes modelled, only three (absorption of long-wave atmospheric radiation, evaporative heat exchange and the convective exchange of sensible heat) are both meteorologically forced and occur during nighttime.
All three of these were found to have undergone shifts from the 1950s to the 1990s, so that each of these three processes can be surmised to have contributed significantly to the overall secular increase in lake temperatures.
Summary
High degree of regional warming that occurred in the European Alpine area during the 20th century
From the 1950s to the 1990s, high warming rates (∼0.24 K per decade) in the uppermost 20 m of the lake (i.e., the epi/metalimnion) combined with lower warming rates (∼0.13 K per decade) below 20 m (i.e., in the hypolimnion), have resulted in a 20% increase in thermal stability and a consequent extension of 2–3 weeks in the stratification period.
The temporal structure of the temperature of the surface mixed layer of Lake Zurich faithfully reflects that of the regional daily minimum air temperature, but not that of the daily maximum.