read - Eulakes

European Geosciences Union
General Assembly 2013
Vienna, Austria
10 April 2013
On the impact of climate change on surface
water temperature of Lake Garda
Sebastiano Piccolroaz
Marco Toffolon
Department of Civil, Environmental
and Mechanical Engineering
University of Trento, Italy
marco.toffolon@unitn.it
Maria-Caterina Sighel
Environmental Protection Agency
of the Province of Trento, Italy
Mariano Bresciani
Optical Sensing Group
Institute for Electromagnetic Sensing of the Environment
National Research Council of Italy
Milano, Italy
The problem
Case study: Lake Garda (Italy)
air temperature
Volume 49 km³
Surface 368 km²
climate change
Length 52 km
Width 16 km
Max depth 346 m
Mean depth 133 m
lake water temperature
The model air2water
Heat budget in the
well-mixed surface layer
model
Main forcing factor: air temperature Ta
Main result: surface water temperature Tw
Ta
physical parameters
Tw
S. Piccolroaz, M. Toffolon, and B. Majone
A simple lumped model to convert air temperature into surface water temperature in lakes
Hydrol. Earth Syst. Sci. Discuss., 10, 2697–2741, 2013
(discussion open until 30th April: www.hydrol-earth-syst-sci-discuss.net/10/2697/2013/doi:10.5194/hessd-10-2697-2013)
The model air2water
heat budget with a simplified parameterization of the net heat exchange
temporal
evolution
of water
temperature
seasonal forcing
(hp. sinusoidal)
residual
“gradient” with
atmosphere
residual effect of
water temperature
effect of time-dependent stratification:
dimensionless depth of the surface well-mixed layer
(Tr is the deep temperature, for dimictic lakes =4°C)
different versions of the model:
• 8-parameter (pi, i=1..8)
• 6-parameter (pi, i=1..6)  simplified inverse stratification (winter)
• 4-parameter (pi, i=3..6)  seasonal forcing included in the other periodic terms (p4, p5)
air2water - an application to Lake Superior
selection of parameters based on Nash efficiency index – ex. 4 par. model
(108 Monte Carlo model realizations with uniform random sampling)
calibration
results: model vs. measurements
validation
T air
meas.
T water
model
4 par.
model
8 par.
meas.
Piccolroaz et al., HESS-D 2013
air2water – using satellite data (Lake Superior)
T air
meas.
T water
model
4 par.
model
8 par.
meas.
(data: Great Lakes Environmental Research Laboratory,
NOAA National Oceanic and Atmospheric Administration)
lake thermal inertia (large volume)
 air-water temperature hysteresis
linear regression is wrong!
air/water temperature records in the northern (deeper)
part: APPA buoy, IASMA meteo, MODIS satellite
Lake Garda: available data
water temperature buoy
• depth = 10 m
(within the epilimnion)
•
•
years 2009-2012
frequency: 1 hour
•
 aggregated to 1 day
several missing values
air temperature
• 2009-2013
• 1 hour
 1 day
water temperature
• profiles 0-270 m
• 1990-2011
• monthly
surface water
temperature
from MODIS
satellite sensor
• 2004-2012
• ~daily
Lake Garda: satellite data vs. buoy measurements
buoy  hysteresis air-water
MODIS  ~linear dependence with T air (no hysteresis)
 too high summer temperatures
 too low winter temperature
Lake Garda: satellite data vs. measurements
T air – T water hysteresis (mean year)
MODIS
buoy
minimum T water ~8°C
(Lake Garda is oligomictic)
MODIS: lake surface temperature
buoy at 10 m (but well-mixed surface
layer always >= 10 m)
Lake Garda: air2water applied on measurements at buoy
air2water vs. linear regression
linear regression:
T [°C]
2009
2010
2011
t [day]
2012
•
underestimation
of high water
temperatures
•
wrong phase
(especially in
winter-spring)
Lake Garda: air2water applied on measurements at buoy
air2water vs. linear regression
T air – T water hysteresis
parity diagram
linear regression: inconsistent for extrapolation (e.g. rising temperature)
Lake Garda: climate change scenarios
estimates of the increase of air temperature in the region of Lake Garda
Züger J., Knoflacher M., AIT Austrian Institute of Technology GmbH
Uncertainties of scenarios - Regional climate change scenario
Deliverable 4.3.3, Project EULAKES, 2012
variation of water temperature in Lake Garda?
“delta” method:
• estimate of variation of air temperature from now to 2100 (in decades)
• apply the variation to measured values of air temperature (four years 2009-2012)
air2water
• variation of water temperature in the four reference years in the future decades
Lake Garda: climate change scenarios
(four years)
time
(decades)
time
(decades)
red = now
from yellow to blue = decades from 2021-2031 to 2091-2101
Lake Garda: climate change scenarios
(mean year)
(winter)
(spring)
(summer)
(autumn)
from yellow to blue = decades from 2021-2031 to 2091-2101
Conclusions
Lake Garda:
• an increase of air temperature up to 6°C (2100) reflects into
an increase of water temperature up to 4°C
• the increase is larger in summer
(when air temperature is much higher than current water temperature
and the epilimnion is thinner)
• the increase is milder in winter
(when increased air temperature is similar to current water temperature
and the epilimnion is thicker)
General:
• a model to convert air temperature to water temperature in lakes
• conversion and downscaling at the same time
• significant improvements with respect to standard techniques
• application to climate change scenarios (requiring only air temperature)
European Geosciences Union
General Assembly 2013
Vienna, Austria
10 April 2013
On the impact of climate change on surface
water temperature of Lake Garda
Sebastiano Piccolroaz
Marco Toffolon
Department of Civil, Environmental
and Mechanical Engineering
University of Trento, Italy
marco.toffolon@unitn.it
Maria-Caterina Sighel
Environmental Protection Agency
of the Province of Trento, Italy
Mariano Bresciani
Optical Sensing Group
Institute for Electromagnetic Sensing of the Environment
National Research Council of Italy
Milano, Italy