MODELLING OF THE HYDROLOGICAL REGIME OF THE LAKE NEUSEIDL CATCHMENT AT GLOBAL WARMING USING THE EMPIRICAL PALEOCLIMATIC SCENARIOS Natalia Lemeshko Tatiana Gronskaya Irena Borzenkova State Hydrological Institute State Hydrological Institute 2-nd Liniya 23 2-nd Liniya 23 St.Petersburg St.Petersburg Russia Russia Tel. 7(812) Tel. 7(812) Fax: 7(812) Fax: 7(812)

Lakes all over the world are known as natural reliable moisture integrators, which reflect both long- and short-term climate fluctuations Hydrological regime of lakes and its changes are determined by a great number of interconnected factors Hydrological regime of lakes and its changes are determined by a great number of interconnected factors

Modern environmental and climate change, caused by natural and man-made factors, drives to drives to important changes in hydrological regime оf lakes important changes in hydrological regime оf lakes Lakes also influence on their coastal areas Lakes also influence on their coastal areas These changes should have both positive and negative consequences of different scale in ecological state and humans These changes should have both positive and negative consequences of different scale in ecological state and humans

Modern regime of LAKE NEUSEIDL The estimation of current changes of Neuseidl Lake level has not been our task. The estimation of current changes of Neuseidl Lake level has not been our task. But in order to understand the problem of its level change during last decades, we evaluate its water balance components for study period. But in order to understand the problem of its level change during last decades, we evaluate its water balance components for study period.

The equation of the Neuseidl Lake water balance is as H WB =Q in /S+Q gw /S+P-E-Q/S H WB =Q in /S+Q gw /S+P-E-Q/Swhere Qin- inflow by rivers into the lake, Mio cub m Q gw -underground inflow, Mio cub m P- precipitation onto the lake water surface, mm E - Evaporation from the lake, mm Q - outflow from the lake, Mio cub m S- the lake water surface, sq. km S- the lake water surface, sq. km H WB - changes of the lake level, mm

Data Air temperature time-series for the period Air temperature time-series for the period Precipitation (2004) Precipitation (2004) Inflow (2004) Inflow (2004) Outflow (2004) Outflow (2004) Water level (2004) Water level (2004) So we can calculate water balance for

THE LAKE NEUSEIDL LEVEL We reconstructed natural water level by water balance equation since 1965, when lake was damed «natural» level, the lake with natural outflow by chanal observed level for reconstructed natural level THE LAKE NEUSEIDL LEVEL We reconstructed natural water level by water balance equation since 1965, when lake was damed «natural» level, the lake with natural outflow by chanal observed level for reconstructed natural level

The reconstructed lake level would be higher by about 1 m if it was not artificially regulated by channel The reconstructed lake level would be higher by about 1 m if it was not artificially regulated by channel Under natural conditions the level should fall down only since 1987 and the lowest level (for last 35 years) should be observed in Under natural conditions the level should fall down only since 1987 and the lowest level (for last 35 years) should be observed in Reconstructed level is higher than level for the whole period of observations ( ) Reconstructed level is higher than level for the whole period of observations ( )

Fluctuation of the Neuseidl Lake Level Modern period of the Neuseidl lake hydrological regime consists of transgressions and regressions, resulting from fluctuations of its water balance components: Modern period of the Neuseidl lake hydrological regime consists of transgressions and regressions, resulting from fluctuations of its water balance components: Increase of level in Increase of level in Decrease till 1949 Decrease till 1949 Level would increase more than for 1 m in the 60-s if it was not regulated Level would increase more than for 1 m in the 60-s if it was not regulated Regulation decreases the amplitude of lakes level fluctuations Regulation decreases the amplitude of lakes level fluctuations

Our task: to estimate future level fluctuation of the lake using the paleoclimatic reconstruction This study is available because The Earths history knows the epochs with warmer climate than current. Using our knowledge about environment in these epochs, we should enlarge our ideas about the response of the hydrological regime of rivers, lakes and seas to global warming. The Earths history knows the epochs with warmer climate than current. Using our knowledge about environment in these epochs, we should enlarge our ideas about the response of the hydrological regime of rivers, lakes and seas to global warming.

In accordance with the forecast of global climate change globally averaged air temperature is expected to be In accordance with the forecast of global climate change globally averaged air temperature is expected to be 1 C above the pre-industrial value by C above the pre-industrial value by ,8-2,6 C by 2050 and 1,4-5,9 C by 2100 (IPCC, 2001) These levels of global warming correspond to warm epochs of geological past : These levels of global warming correspond to warm epochs of geological past : Holocene optimum (6-5 KA B.P.), when global temperature was about 1 C higher than modern one Holocene optimum (6-5 KA B.P.), when global temperature was about 1 C higher than modern one Last Interglacial -Eem ( KA B.P.) corresponds to global warming about 1,5-2 С Last Interglacial -Eem ( KA B.P.) corresponds to global warming about 1,5-2 С Pliocene climatic optimum (4.3-3,3 Myr B.P.) when global temperature was about 3-4 C higher than modern one Pliocene climatic optimum (4.3-3,3 Myr B.P.) when global temperature was about 3-4 C higher than modern one ( Anthropogenic climate change, Ed. By Budyko, &Izrael,1987 ) ( Anthropogenic climate change, Ed. By Budyko, &Izrael,1987 )

3. Empirical data for the last century indicate growth of the global average air temperature by about 0.60 ±0.3 0 C since the late of the 19th century New analyses of proxy data for the Northern Hemisphere indicate that the increase in temperature in 20th century is likely to have been the largest of any century during the 1000 years. The 1990s were the warmest decade in the time series. New analyses of proxy data for the Northern Hemisphere indicate that the increase in temperature in 20th century is likely to have been the largest of any century during the 1000 years. The 1990s were the warmest decade in the time series. The warmest three years of the entire series have been 2002&2003 and 1998, with the latter the warmest at 0.58°C above the mean. The warmest three years of the entire series have been 2002&2003 and 1998, with the latter the warmest at 0.58°C above the mean. The eleven warmest years globally have now occurred in the 1990s and 2000s. The eleven warmest years globally have now occurred in the 1990s and 2000s. They are, in descending order They are, in descending order 1998, 2003&2002(joint), 2001, 1997, 1995, 1998, 2003&2002(joint), 2001, 1997, 1995, 1990 & 1999 (joint), 1991 & 2000 (joint) & 1999 (joint), 1991 & 2000 (joint).

Changes of water balance components were estimated for global warming by 1 C, 2 and 3 C for Lake Neusiedl See and its catchment. Heat-water balance model has been developed to calculate the changes in climate and hydrological parameters the changes in climate and hydrological parameters with the global warming with the global warming

METHOD: METHOD: Budykos method for assessment of evaporation from land surface, adapted to computing all components of heat and water balance Budykos method for assessment of evaporation from land surface, adapted to computing all components of heat and water balance SCENARIOS: SCENARIOS: The paleoclimatic maps-reconstruction: winter and summer air temperature The paleoclimatic maps-reconstruction: winter and summer air temperature annual precipitation annual precipitation for global warming on 1, 2 and 3С for global warming on 1, 2 and 3С

Heat-water balance method A method proposed by M.I. Budyko is used to determine evapotranspiration. A method proposed by M.I. Budyko is used to determine evapotranspiration. All the main factors determining evaptraspiration are taken into account in this method – radiation balance, temperature and humidity of the air, and turbulent exchange. All the main factors determining evaptraspiration are taken into account in this method – radiation balance, temperature and humidity of the air, and turbulent exchange.

Evapotranspiration Evapotranspiration Eo is computed by formula which relates the proportion of evaporation from a wet surface to the air humidity deficit determined from the temperature of the evaporating surface. Evapotranspiration Eo is computed by formula which relates the proportion of evaporation from a wet surface to the air humidity deficit determined from the temperature of the evaporating surface. E 0 = D ( q s _ q ), E 0 = D ( q s _ q ), where Eo is evapotranspiration, = 1, g/cm 3 – air density, where Eo is evapotranspiration, = 1, g/cm 3 – air density, D = 0,63 cm /s – integral coefficient of the external diffusion, D = 0,63 cm /s – integral coefficient of the external diffusion, q s – specific humidity of the air saturated by water vapour at the surface temperature Tw; q s – specific humidity of the air saturated by water vapour at the surface temperature Tw; q is specific humidity of the air. q is specific humidity of the air.

The coefficient of external diffusion D The value of the coefficient of external diffusion D is taken as constant, being equal to 0,63 cm s -1. The value of D differs with climatic conditions, but these changes have been sufficiently studied to differentiate D according to a season, climate atc. The value of the coefficient of external diffusion D is taken as constant, being equal to 0,63 cm s -1. The value of D differs with climatic conditions, but these changes have been sufficiently studied to differentiate D according to a season, climate atc. The estimates made by Seryakova, show that if coefficientD is multiplied even by 1,5 times comparatively small changes in evapotranspiration will take place. This makes it possible to use the constant value of D for the computation of Eo, without fear that there will be substantial errors in Eo. The estimates made by Seryakova, show that if coefficientD is multiplied even by 1,5 times comparatively small changes in evapotranspiration will take place. This makes it possible to use the constant value of D for the computation of Eo, without fear that there will be substantial errors in Eo.

The temperature of the active surface Tw The temperature of the active surface Tw is determined from the equation of the heat balance of the land under conditions of adequate moisture The temperature of the active surface Tw is determined from the equation of the heat balance of the land under conditions of adequate moisture R=LEo+H+B, R=LEo+H+B, where the radiation balance R=Ro-4ST з (Tw-T) where the radiation balance R=Ro-4ST з (Tw-T) Here Ro is the radiation balance of the wet surface, determined by computation of the effective radiation from air temperature T. Here Ro is the radiation balance of the wet surface, determined by computation of the effective radiation from air temperature T. S is a coefficient of reflectivity characterizing the properties of the radiating surface; S is a coefficient of reflectivity characterizing the properties of the radiating surface; is Stefans constant; is Stefans constant; Turbulent heat flax H=c p D(Tw-T), Turbulent heat flax H=c p D(Tw-T), where c p is heat capacity of the air; where c p is heat capacity of the air; B is heat flux between the surface of the land and lower layers; B is heat flux between the surface of the land and lower layers; L is latent heat of evaporation. L is latent heat of evaporation.

Substituting expressions for R, H, and Eo in the heat –balance equation, we obtain Substituting expressions for R, H, and Eo in the heat –balance equation, we obtain Ro-B=L D(qs-q)+( cpD+4STз)*(Tw-T) The radiation balance Ro and heat flux in soil B' (by semi-empirical equations) are computed, The radiation balance Ro and heat flux in soil B' (by semi-empirical equations) are computed, T and q are known from meteorological observations; the values of Tw and qs, are determined from equation of radiation balance, as these values being related to each other by empirical formulas for the dependence of water-vapour pressure upon temperature (e.g. formula of Magnus). T and q are known from meteorological observations; the values of Tw and qs, are determined from equation of radiation balance, as these values being related to each other by empirical formulas for the dependence of water-vapour pressure upon temperature (e.g. formula of Magnus)..

The method is based on combined solution of energy and water balance r=E+f+ΔW equations and on two empirical dependences: The evaporation rate on soil moisture content The evaporation rate on soil moisture content if W W 0 Е=Е 0, if W W 0 E=E 0 ( W/ W 0 ), if W W 0 if W W 0Where W – mean annual soil moisture content W – mean annual soil moisture content E 0 – evapotranspiration E 0 – evapotranspiration E – evaporation E – evaporation W 0 = mm, limited value of soil moisture W 0 = mm, limited value of soil moisture Surface runoff on precipitation and soil moisture Surface runoff on precipitation and soil moisture if rE 0 : Wk=200 mm – productive field moisture capacity Wk=200 mm – productive field moisture capacity u – index, depending on the intensity of precipitation u – index, depending on the intensity of precipitation f – runoff f – runoff r – precipitation r – precipitation

The basic principles of applying the method 1. Determination of mean water balance components under modern climatic conditions 2. Calculation of water balance components for different scales of the global warming using paleoclimatic scenarios

Mean monthly values of the heat and water balance components for the lakes basin have been calculated using the observed data on modern climate: Mean monthly values of the heat and water balance components for the lakes basin have been calculated using the observed data on modern climate: long-term mean monthly air temperature, air humidity deficit, total cloudiness, surface albedo, total solar radiation, precipitation. long-term mean monthly air temperature, air humidity deficit, total cloudiness, surface albedo, total solar radiation, precipitation. We used the current climatic data averaged for air temperature, precipitation, cloudiness, air humidity We used the current climatic data averaged for air temperature, precipitation, cloudiness, air humidity for the Vienna meteorological station. for the Vienna meteorological station.

First step By mean monthly air temperature, air humidity, precipitation, cloudiness, surface albedo, total solar radiation, Have been calculated Mean monthly evapotranspiration, runoff, evaporation from soil, soil moisture content of active (1 m ) soil layer soil layer

Second step: water balance components for 1, 2 and 3°C global warming I. Borzenkova reconstructed climate for this warm epochs These paleoclimatic reconstructions are: the maps the maps for the Northern Hemisphere for the Northern Hemisphere of winter and summer air temperature and annual precipitation we determined temperature and precipitation according to these paleoclimatic reconstructions for the Neuseidl Lake basin temperature and precipitation according to these paleoclimatic reconstructions for the Neuseidl Lake basin

Annual precipitation (mm) in deviation from the normal for the Holocene optimum (6-5 KA BP) by I.I. Borzenkova, 1992 Annual precipitation would increase by 10 mm

Summer air temperature in deviation from the normal for the Holocene optimum (6-5 KA BP) by I.I. Borzenkova, 1992 Summer temperature from mean for ,1 C Winter temperature from mean for C

Changes in temperature and precipitation of the lake Neuseidl basin with global warming by 1°, 2 and 3 C Table shows that the climatic characteristics of the study area should differ significantly for the global warming by 1, 3 and 2ºC. The paleoclimatic data assume the increase of precipitation in 50% for the global warming by 2ºC and twice growth of air temperature in comparison with the 1ºC GW. The largest increase has been predicted for winter temperature for the scenarios. Scale of global warming 1 C2 C3 C Parameters according to scenario Air temperature, C Summer Air temperature, C Winter Annual precipitation, mm

Second step Method adaptation Method adaptation Some additional assumptions have been made to introduce yearly and seasonal changes of paleoclimate parameters to mean monthly temperature and precipitation: Some additional assumptions have been made to introduce yearly and seasonal changes of paleoclimate parameters to mean monthly temperature and precipitation: (1) spring and autumn surface air temperature changes are equal to the averaged winter+summer temperature departures (2) Within year precipitation distribution would not change and monthly precipitation assumed to be proportional to relative change of annual precipitation with global warming

To estimate the water balance of the Neuseidl Lake basin for the global warming by 1 and 2° C we need the following information: air humidity, cloudiness, surface albedo, total solar radiation Additional hypotheses have been used to get the values of these meteorological parameters for the climatic conditions of global warming Additional hypotheses have been used to get the values of these meteorological parameters for the climatic conditions of global warming Relative air humidity Relative air humidity Total cloudiness const Total cloudiness const Total solar radiation Total solar radiation Adaptation of calculation scheme changes of albedo changes of the warm period duration CO2 contribution into atmospheric counter-radiation

RESULTS Changes in climatic and hydrological parameters for 1, 2 and 3 С global warming Changes of mean monthly Changes of mean monthly Evaporation Evaporation Runoff Runoff Soil moisture content Soil moisture content Changes of Changes of Duration of warm period Duration of warm period Dates of forming/melting stable snow cover Dates of forming/melting stable snow cover

Changes in climatic and hydrological parameters of lake with global warming by 1, 2 and 3 C. The mean values of water balance components have been calculated for the study area. Then their values have been transformed according to climate scenarios: The duration of warm period, which is affected only by air temperature, increases considerably: more than for a month. Evapotranspiration would be higher than mean annual one (730 mm/year) by about 45 mm/year (6%) with global warming on 1 C and by 81 mm/year (11%) with global warming on 2 Cand C. by 81 mm/year (11%) with global warming on 2 Cand 3 C. The increase of air temperature, duration of warm period and potential evaporation leads to the increase of evaporation from land surface The increase of air temperature, duration of warm period and potential evaporation leads to the increase of evaporation from land surface (2-40 %). (2-40 %). Scale of global warming 1 C2 C3 C Parameters according to scenario Air temperature, C Summer Air temperature, C Winter Annual precipitation, mm Calculation Annual runoff, mm (%) -2 (-3%)+50 (83%) +26 (43%) Potential evaporation, mm (%) +45 (6%)+81 (11%) +80 (11%) Evaporation from land surface, mm (%) +12 (2%)+250 (41%) +152 (25%) Duration of warm season, days +41

Changes in climate parameters of Neuseidl See catchment with 2 0 C Evapotranspiration 11% Evaporation from land surface 40% Precipitation 300 mm (48%) Changes in Summer temperature 2,5 0 C Winter temperature 3 0 C Duration of warm period increases on 41 days inflow 83 %

Income part of WB (Precipitation and inflow) As it comes from previous study, annual runoff is strongly affected by precipitation. As it comes from previous study, annual runoff is strongly affected by precipitation. Annual precipitation should not sufficiently increase with 1C global warming (according to the Holocene optimum regional scenario by 10 mm only) and it should be 50% higher for 2 0 C warming than current mean annual precipitation. Annual precipitation should not sufficiently increase with 1C global warming (according to the Holocene optimum regional scenario by 10 mm only) and it should be 50% higher for 2 0 C warming than current mean annual precipitation. The results of calculation exhibit, that the changes in annual runoff are different for different scales of warming. The annual runoff would be 3% lower than mean annual with 1C warming. The most dramatic changes should be characteristic for 2C GW: annual runoff in the lake catchment should grow for 50 mm or 83% according to increase of predicting precipitation and modelling. The results of calculation exhibit, that the changes in annual runoff are different for different scales of warming. The annual runoff would be 3% lower than mean annual with 1C warming. The most dramatic changes should be characteristic for 2C GW: annual runoff in the lake catchment should grow for 50 mm or 83% according to increase of predicting precipitation and modelling.

These estimates of the water balance components for the lakes catchment are the basis for forecasting possible changes of the lakes level. These estimates of the water balance components for the lakes catchment are the basis for forecasting possible changes of the lakes level. But there is an important special feature of Lake Neusiedl both within a year and from year to year: The considerable variability of the lakes level, its water surface area and storage Uncertainty The first idea was to use the mean annual lake level and corresponding it lakes surface and catchment areas for as initial level for calculating of the lakes hydrological regime under global warming. The first idea was to use the mean annual lake level and corresponding it lakes surface and catchment areas for as initial level for calculating of the lakes hydrological regime under global warming. ?

Dependence between lakes water level and its surface area To study all range of possible level changes in future we have to use different versions. The first assumption is that water level is equal to a mean annual ( version A) The second- level would be equal to maximum observed (version B) The second- level would be equal to maximum observed (version B) The third- level is equal to minimum observed one during (version C) The third- level is equal to minimum observed one during (version C) The forth - the catchment area is equal to 680 km 2 and lake surface area is 320 km 2 (D). The forth - the catchment area is equal to 680 km 2 and lake surface area is 320 km 2 (D). As the outflow is regulated we used its mean volume for (versions A and D).

Parameters of lake Parameters A Mean level B maximal Level C minimal LevelD Lake level, m BS 115,1115,9114,6116,4 Watershed area (km 2 ) 829, ,9680 Water-surface lake area (km 2 ) 170,1312,0137,1320

Water balance components Mean Climate Condition Version A D Precipitation (Mio m3) Inflow (Mio m3) Evapotranspiration (Mio m3) Volume change (Mio m3) Level change (m) Level, m Outflow (Mio m3), mean 27.2 Volume change (Mio m3) -6.9 Level change (m), if outflow =mean Level, m Modelling mean annual lakes water balance The mean annual level for (when lakes level was not artificially regulated) has been used as the basic level for calculations. Calculations of the lakes water balance show the instability of its level for the period : its mean growth was equal to 23 cm by A version and 6 cm by D version. Calculations of the lakes water balance show the instability of its level for the period : its mean growth was equal to 23 cm by A version and 6 cm by D version.

Water balance components Global warming by 1 C Versions (level) A 115,1 B 115,9 C 114,6 Precipitation (Mio m3) Inflow (Mio m3) Evapotranspiration (Mio m3) Volume change (Mio m3) Level change (m)0.180, Level, m , Outflow (Mio m3), mean27.2 Volume change (Mio m3)3,9 Level change (m), if outflow =mean 0.02 Level, m Global warming by 1°C Version A. For the Holocene optimum the growth of air temperature leads to the increase of potential evaporation, at the same time precipitation growth is equal to 10 mm. As the result, the inflow is slightly lower than norm. Such combination of the water balance components leads to the increase of lakes level for 18 cm (without outflow) and for 2 cm (with mean volumes of outflow). Version B. The maximum observed annual lake level before 1965 is 115,9 m, corresponding lake's surface area is 312 km 2 and watershed area km 2. The lake level changes should be insufficient. Version C. The minimum initial lakes level, corresponding lakes surface area km 2 and the catchment area 863 km 2. Calculations according to this version show the largest growth of the lakes level – by 26 cm.

So the assumed for the Holocene scenario climate change should not result in the decreasing of the lake's level. The most possible lake level should be in the range 115,3 (Version A )-114,86 m (Version С). This range includes Version A with the mean outflow from the lake equals to 27,2 Mio cub m. So the assumed for the Holocene scenario climate change should not result in the decreasing of the lake's level. The most possible lake level should be in the range 115,3 (Version A )-114,86 m (Version С). This range includes Version A with the mean outflow from the lake equals to 27,2 Mio cub m.

Water balance components Global warming by 2 C Versions (level) A 115,1 B 115,9 C 114,6 Precipitation (Mio m3) Inflow (Mio m3) Evapotranspiration (Mio m3) Volume change (Mio m3) Level change (m) Level, m Outflow (Mio m3), mean 27.2 Volume change (Mio m3) 90.5 Level change (m), if outflow =mean 0.53 Level, m Global warming by 2°C. The paleoclimatic data assume the increase of precipitation for about 50% and twice growth of air temperature in comparison with the Holocene scenario. The paleoclimatic data assume the increase of precipitation for about 50% and twice growth of air temperature in comparison with the Holocene scenario. Such sufficient changes should result in the lakes' storage change equal to the current storage of the lake for mean annual conditions. Such sufficient changes should result in the lakes' storage change equal to the current storage of the lake for mean annual conditions. So by version A the storage should change on 118 Mio cub m, by B- on 124 Mio cub m, C- on 116 Mio cub m, while the mean annual lake storage corresponding to the mean annual level (115,11 m) is equal to 133,4 Mio m3. The most considerable changes of the lake level should be for the lowest lake level (Version C) – level increasing by about 1 m. So by version A the storage should change on 118 Mio cub m, by B- on 124 Mio cub m, C- on 116 Mio cub m, while the mean annual lake storage corresponding to the mean annual level (115,11 m) is equal to 133,4 Mio m3. The most considerable changes of the lake level should be for the lowest lake level (Version C) – level increasing by about 1 m.

Global warming by 3°C. Water balance components Global warming by 3C Versions (level) A 115,1 B 115,9 C 114,6 Precipitation (Mio m3) Inflow (Mio m3) Evapotranspiration (Mio m3) Volume change (Mio m3) Level change (m) Level, m Outflow (Mio m3), mean27.2 Volume change (Mio m3) 50.1 Level change (m), if outflow =mean 0.29 Level, m115.4 The paleoclimatic data assume the increase of precipitation for about 27% and twice growth of air temperature in comparison with the Holocene scenario and equal to Eem scenario. This scenario does not show such sufficient changes as Last Interglacial – Eem This scenario does not show such sufficient changes as Last Interglacial – Eem. The most considerable changes of the lake level should be for the lowest lake level (Version C) – level increasing by about 0.6 m.

Water balance components D GW levelGW=0GW=1 o C GW=2 o C Precipitation (Mio m3) Inflow (Mio m3) Evapotranspiration (Mio m3) Volume change (Mio m3) Level change (m) Level, m Outflow (Mio m3), mean 27.2 Volume change (Mio m3) Level change (m), if outflow =mean Level, m Version D. Calculations according to the watershed area 680 km 2 and water lake area 320 km 2 show the highest lakes level position (116,4-116,79) both for mean climate and for global warming scenarios. Only in this case falling of lake level should be for global warming by 1°C ( if outflow is equal to 27,2 Mio m3 ). ( if outflow is equal to 27,2 Mio m3 ). GW

We study 3 scenarios and four initial lakes level. As Neuseidl See is artificially regulated now, we should calculate lakes level change beginning from the initial level - 115, 49 m

The level change The level change (assessed by paleoscenario of the Holocene climatic optimum) (assessed by paleoscenario of the Holocene climatic optimum) may be used for the calculation of the Neuseidl See level in the future may be used for the calculation of the Neuseidl See level in the future (the last year for which we (I) have the instrumental data is 2000)

Water balance componentsHolocene as scenario to Initial conditions Level, m115,49 Lakes area, sq km274 Lakes catchment, sq km726 Precipitation according to scenario of the Holocene Precipitation (Mio m3)185 Modeling values Inflow (Mio m3)42 Evapotranspiration (Mio m3)212 Outflow (Mio m3), mean27.2 Volume change (Mio m3)-12.2 Level change (m)-0.04 Level, m Mean annual Level, m for

H ow is modern regional climate change similar in Europe and in the study basin to paleoclimatic reconstruction of the Holocene optimum? H ow is modern regional climate change similar in Europe and in the study basin to paleoclimatic reconstruction of the Holocene optimum? We have calculated anomalies of air temperature and precipitation for the Northern Hemisphere and compared them with regional reconstruction for the Holocene. We have calculated anomalies of air temperature and precipitation for the Northern Hemisphere and compared them with regional reconstruction for the Holocene.

The anomalies are very similar The anomalies are very similar to the Holocene temperature: winter +1 ° C (1,5) summer +0,7 °C (1,1) summer +0,7 °C (1,1) Annual precipitation 0 mm (10 mm) Annual precipitation 0 mm (10 mm)

Alternative historical analogue approach The hydrological conditions of extreme years have been used for these purposes The years (periods) with annual temperature/precipitation higher than normal for recording period for the lake catchment. Now this approach is not available for Neuseidl Lake as the data needed Now this approach is not available for Neuseidl Lake as the data needed are limited by (inflow data) are limited by (inflow data)

1965- Eem scenario But even within this short period one can select a year (1965), when annual precipitation is by 300 mm higher than mean annual. This anomaly corresponds to Eem scenario for the study area. The increase in precipitation results in the increase of the lake level up to 116,21 in 1966 (by 62 cm higher than in previous year) (reconstructed level)

Quick review of the lakes history : The lake disappeared frequently To improve this phenomenon in 1096, 1318, , and To improve this phenomenon we need the proxy data of climate conditions in the study area. One source: the proxy data collected by Borisenkov from ancient manuscripts since 1140 ( Extreme climate conditions over Europe, 1975) But this information covers a very wide region It is not clear enough should it be useful for the Vienna region Important note It is well known that It is well known that 8 th - 13 th centuries was the period of the minor climate optimum. 8 th - 13 th centuries was the period of the minor climate optimum. 14th-18th centuries was the period of Climate cooling. 14th-18th centuries was the period of Climate cooling. So the lake disappeared both under warm climate (1096) So the lake disappeared both under warm climate (1096) and under cooling ( and under cooling ( 1318, )

Our study shows that there is strong correlation between precipitation over the lake basin and lake storage change under natural conditions If precipitation are lower than 540 mm – the lake water volume decreases. If precipitation are lower than 540 mm – the lake water volume decreases.

Conclusions We studied three scenarios and four initial lakes level. We studied three scenarios and four initial lakes level. For one variant of calculation the decrease of level has been obtained – version D (watershed area 680 km 2 and water lake area 320 km 2, level 116,4). For one variant of calculation the decrease of level has been obtained – version D (watershed area 680 km 2 and water lake area 320 km 2, level 116,4). Only in this case slight falling of lake level ( 60 mm) should be for global warming by 1°C ( 60 mm) should be for global warming by 1°C ( if outflow is equal to 27,2 Mio m3 ).

Conclusions Global climate changes influence natural and human systems and form new tendencies in the land hydrology, as well as in hydrological regime of lakes. Global climate changes influence natural and human systems and form new tendencies in the land hydrology, as well as in hydrological regime of lakes. The paleoclimatic methods usually consider the hydrological regime of lakes as the reliable indicator of changes in natural ecosystems, temperature and moisture regime for different epochs in the past. Now we made first attempt to use paleoclimatic reconstruction to forecast the hydrological regime of the lake with expected changes of climate. Used scenarios indicate that regional temperature would be accompanied by different changes in precipitation and lakes level. The paleoclimatic methods usually consider the hydrological regime of lakes as the reliable indicator of changes in natural ecosystems, temperature and moisture regime for different epochs in the past. Now we made first attempt to use paleoclimatic reconstruction to forecast the hydrological regime of the lake with expected changes of climate. Used scenarios indicate that regional temperature would be accompanied by different changes in precipitation and lakes level.

The estimates of water balance change should be considered from two points of view: The estimates of water balance change should be considered from two points of view: (1) information for estimation of future water resources with anthropogenic climate change (1) information for estimation of future water resources with anthropogenic climate change (2)reconstruction of hydrological regime of the Lake for the warm epochs of the past and creation a new basis for improving GSM. (2)reconstruction of hydrological regime of the Lake for the warm epochs of the past and creation a new basis for improving GSM.

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