Dipartimento ICEA

UNIVERSITÀ DEGLI STUDI DI PADOVA

Federico De Piccoli

RelatoreIng. Gianluca Botter

CorrelatoreProf. Ing. Andrea Rinaldo

Academic year 2011-2012

STREAMFLOW REGIMESTREAMFLOW REGIME IN SNOW DOMINATED IN SNOW DOMINATED

CATCHMENTSCATCHMENTS

ENAC – EPFLLaboratory of Ecohydrology

INTRODUCTIONINTRODUCTIONSnow covered landscape has acquired notable importance.

In particular in relation with:ENVIRONMENTALENERGETICSOCIAL ACTIVITIES

WINTER STREAMFLOW DYNAMICSWINTER STREAMFLOW DYNAMICS

TEMPERATURE GOVERNS THE PRECIPITATION REGIME

REDUCED EFFECT OF EVAPO-TRANSPIRATION

INCRESING WATER STORAGE RELEASED IN SPRING

RETARDING EFFECT IN RELEASE DUE TO SNOW PERSISTENCE

THIS AFFECTS VEGETATION, SOIL AND DISCHARGE DYNAMICSTHIS AFFECTS VEGETATION, SOIL AND DISCHARGE DYNAMICS

…a stochastic approach…

TEMPERATURE IS THE MAIN DRIVERTEMPERATURE IS THE MAIN DRIVER 3000

2500

2000

1500

1000[m asl]

THESE THREE ZONES ARE CHARACTERIZED BY:

• NO SNOW

• SNOW EVENTS BUT NO ACCUMULATION

• ONLY ACCUMULATION

We divide the fractions as function of Tms

Image extracted from DTM, Boite closed at Cancia basin

Tms = Mean Seasonal TemperatureHypsographic Curve

Representation in the hypsographic

curve.

TO MODEL WINTER STREAMFLOWS …

…WE FOCUS ON ZONES 2 AND 3

2 - ZONE WITH PRIMARLY SNOW EVENTS AND TEMPORARY ACCUMULATION

• Increasing snowfall probability

• Area from 1000 to 2100-2300 [m a.s.l] • Mean discharge equal to mean precipitation

ZONE 2 – ZONE 2 – A TRANSITION ZONEA TRANSITION ZONE

• Responsive fraction

3 - ZONE OF PURE ACCUMULATION

• Tms < - 4 °C• Elevation > 2300 m a.s.l.• Negligible snowmelting

The solution is an atom of probability concentrated in zero pdf(Q)=0

ZONE 3 – ZONE 3 – THE HIGHER FRACTIONTHE HIGHER FRACTION

• Accumulation area

THE THRESHOLD Z*THE THRESHOLD Z*The idea is to assume the existence of a critical elevation Z* that identifies the different part of the basin

Z*=2000-2300 m a.s.l.

Tms ≈ -2 °C

CLIMATIC INFORMATION

GEOMORPHOLOGY

Z*CALIBRATION

PARAMETER

STOCHASTIC ANALYTICAL MODELSTOCHASTIC ANALYTICAL MODEL

(liner reservoir )

Discharge delayed by snow persistence

Daily precipitation(marked Poisson process)

Soil moisture dynamic nearby the field capacity

(marked Poisson process)All rainfall is effective

PQ

Evaluation of Parameters Precipitation parameters

Precipitation series Soil and Vegetation parameters Delayed time of discharge

Mean residence time

(Recession limbs)

Mean time of delay (Temperature series)

Threshold Z* - Rescaling CONTRIBUTING AREA

(Calibration parameter Z*)

ANALYTICAL SOLUTION

PIAVE RIVER BASINPIAVE RIVER BASIN

Surface of the mountain part:3900 km2

Length of the main reach:156 km

7 testing catchments

Nervesa

Fiorentina closed at Sottorovei

Observed

Analytical with snow

Analytical without snow

<Q> [cm/d] CV

Observed 0.0947 0.412

An. Snow 0.0942 0.350

Analytical 0.1363 0.494

RESULTS RESULTS – Piave river basin– Piave river basin

Z*= 2100 m a.s.l.

74 % of area

RESULTS RESULTS – Piave river basin– Piave river basin

Coredevole closed at Saviner

<Q> [cm/d] CV

Observed 0.0927 0.385

An. Snow 0.0912 0.328

Analytical 0.1215 0.493

Z*= 2130 m a.s.l.

71 % of area

Observed

Analytical with snow

Analytical without snow

SWISS BASINSSWISS BASINS26 catchments minimal anthropogenic influence

Some basins present relevant glacial surface

Aletsch glacier in Massa catchment

7 situated in Alpine region

Massa closed nearby Blatten bei Naters

Observed

Analytical modified

Analytical original

<Q> [cm/d] CV

Observed 0.0497 0.483

An. Snow 0.0447 0.442

Analytical 0.1394 0.670

RESULTS – RESULTS – Swiss watershedsSwiss watersheds

Z*= 2210 m a.s.l.

8 % of area

Observed

Analytical with snow

Analytical without snow

RESULTS – RESULTS – Swiss watershedsSwiss watershedsDishmaBach closed at Kriengsmatte (Davos)

Observed

Analytical modified

Analytical original

<Q> [cm/d] CV

Observed 0.0930 0.286

An. Snow 0.0893 0.278

Analytical 0.2461 0.379

Z*= 2290 m a.s.l.

38 % of area

Observed

Analytical with snow

Analytical without snow

DISCUSSION OF RESULTSDISCUSSION OF RESULTS

P[z<Z*]

correlates with the average elevation

Threshold Z* nearly constant in most cases

(independently on geomorphological

attributes)

CONCLUSIONSCONCLUSIONS

》 The model The model reproduces satisfactorily the probability reproduces satisfactorily the probability distributions of the winter dischargesdistributions of the winter discharges observed in both Italian and observed in both Italian and Swiss basins through the calibration of the only parameter Z*Swiss basins through the calibration of the only parameter Z*

》 The values of Z* resulting from the calibration of the model The values of Z* resulting from the calibration of the model with snow, are realistic. with snow, are realistic. Z* is found to be inside the range from Z* is found to be inside the range from 2100 to 2300m a.s.l. in most cases2100 to 2300m a.s.l. in most cases

》 Linear empirical relationships Linear empirical relationships between the fraction of between the fraction of responsive area and the mean and variance of surface heightsresponsive area and the mean and variance of surface heights have been recognized. Such relationships could help improving have been recognized. Such relationships could help improving the predictive power of the modelthe predictive power of the model

THANKS FOR THE ATTENTIONTHANKS FOR THE ATTENTION