Interventions and Climate Change Impacts on the Water Cycle H.P. - - PowerPoint PPT Presentation

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Interventions and Climate Change Impacts on the Water Cycle H.P. - - PowerPoint PPT Presentation

Mar 10, 2024 330 likes •770 views

Discriminating Among Direct Human Interventions and Climate Change Impacts on the Water Cycle H.P. Nachtnebel (IWHW-BOKU) hans_peter.nachtnebel@boku.ac.at Hydropredict2010 H.P. Nachtnebel Organisers and sponsors Hydropredict2010 H.P.

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Hydropredict2010 H.P. Nachtnebel

Discriminating Among Direct Human Interventions and Climate Change Impacts

  • n the Water Cycle

H.P. Nachtnebel (IWHW-BOKU) hans_peter.nachtnebel@boku.ac.at

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Organisers and sponsors

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Organisation of the presentation

  • Objectives and introduction
  • Methodology for assessing human impacts
  • Methodology for climate change impact studies
  • Identified changes and discrimination among CC

and HI

  • Summary and conclusions
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Objectives

  • Analysis of changes in the hydrological cycle
  • Evaluation of methodological approaches to

discriminate among impacts originating from climate change, direct human intervention and natural variability of processes

  • Elaboration of techniques for regional impacts

studies

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Methodology for the assessment of human interventions

  • Time series analysis
  • Experiments
  • Comparative studies
  • Detailed (physical) hydrological models
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Role of scale

From Blöschl et al; 2007

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Human Impacts at different scales

  • Linear, local measures (river channelisation)
  • Regional spatial measures (land use changes)
  • Large scale impacts (land use changes)
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Channelisation of rivers

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Impacts on floods

River training works Partial duration series of floods (1961-1992)

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Climate change ?

  • No significant changes in the annual

precipitation (rather a decrease)

  • No significant change in intensive rainfall

events

Partial duration series of intensive rainfall events (Sajach)

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Comparison of input and output

  • No significant change in precipitation (neither in

total amount, nor in extremes)

  • Increase in flood ferquency and intensity

Input Output Input Output

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Land use changes in a smaller catchment

  • Catchment area about 700 km2
  • Increase in forested area in the last 100 years
  • Channelisation of rivers (up to 30 years flood)
  • Small increase in residential area
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Assessment of Land Use Changes

A distributed model is applied (Debene and Nachtnebel, 2004)

Soil layer Surface runoff Interflow Groundwater flow Snow layer

Snow layer

Surface runoff

Identification of homogeneous regions HBV-type

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Assessment of River Training Works in the Traisen catchment

Debene (2004)

Changes in the peak flow

Peak flow versus changes

Discharge (m3/s)

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Assessment of Land Use Changes

The 1997 flood The 1997 event under conditions of 1880

Change in Peak flow Peak flow (m3/s)

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Impacts on Aral Sea

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Modelling the consequences

  • Modelling and simulation tools

hydrological model water balance model water management models agricultural models economic model ecological model (salinity, variability, depth)

  • Impacts on the water bodies of

Aral Sea

  • Impacts on the Delta areas
  • Impacts on the Priaralie region
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The Aral Sea catchment

  • Growth of population
  • Enlargement of irrigation from 1950-1980
  • Increase of industrial water demand
  • Inefficient water use
  • Lack of international cooperation
  • The inflow to Aral Sea has been drastically

reduced

  • The seasonal cycle has been changed
  • …..
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Conclusions

  • The direct human impacts are measurable
  • The human impacts may change the water

regime drastically

  • Human impacts may chane also the seasonal

cycle

  • What‘s about climate impacts ?
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Methodology for the assessment of climate change impacts

  • Trend analysis of time

series

  • Comparative catchment

studies

  • GCMs and RCMs
  • Downscaling approaches

1912 1969 Vernagt glacier

Wanner et al. 2000

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Do Heavy Rainfall Events Become more Frequent ?

Zahl der Tage mit mehr als 30 mm Niederschlag in Wien Reihe 1961 - 2001

2 1 4 1 1 1 2 3 1 3 1 2 2 1 2 2 1 1 2 1 2 4 3 2 2 2 5 4 2 2

1 2 3 4 5 6 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 Jahr Tage

(after Rudel, ZAMG 2002)

YES !!!!

Number of days per year with more than 30 mm/day (Vienna)

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Do Heavy Rainfall Events Become more Frequent ?

Zahl der Tage mit mehr als 30 mm Niederschlag in Wien Reihe 1903 - 2001

3 2 1 2 3 1 2 3 1 5 1 3 44 00 22 33 2 4 2 1 2 4 2 11 2 1 3 3 4 22 5 22 3 11 00 44 222 11 3 5 2 1 4 1 11 2 3 1 3 1 2 2 1 2 00 2 1 1 2 1 2 4 3 22 2 5 4 2 2

1 2 3 4 5 6 1903 1905 1907 1909 1911 1913 1915 1917 1919 1921 1923 1925 1927 1929 1931 1933 1935 1937 1939 1941 1943 1945 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 Jahr Tage

(after Rudel, ZAMG 2002)

NO !!!!

Number of days per year with more than 30 mm/day (Vienna)

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Possible impacts of climate change on the water balance of Austria

  • Analysis at the catchment scale require high

resolution models (RCMs) or any downscaling approach

  • REMO-UBA RCM was used (10*10 km grid)

Quelle: Formayer

Anomalies in temperature Anomalies in rainfall

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Analysis of RCMs

  • The simulated T and P time series show large

deviations from observations

  • The spatial pattern is shifted
  • Data need adjustment (bias correction,

transfomation, quantile mapping, etc.)

  • The scenario outputs show large differences in P
  • Large uncertainty in the simulated data
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Comparison between simulation and

  • bservation for the control period
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Climate signal in T and P

Temperature Precipitation Difference of long term mean values (1961-1990 und 2036-2065) A1B scenario

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Changes of long term mean values of precipitation

Long term mean annual precipitation

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Hydrological simulation

  • RCM- data were corrected
  • A 1*1 km grid was used for Austria
  • Simualtion at monthly time steps
  • The hydrological model was calibrated for the

past by fitting to 188 gauging stations

  • Glaciers were also simulated
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Some simulation results (1961-1990) flow duration curves

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Veränderungen im Abfluss

A1B scenario Difference between 1961-1990 in mm

  • 2011-2040
  • 2036-2065
  • 2061-2090

Changes in mean annual runoff

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Water balance of Austria

  • The observed trend in the last fifty years is also

found in the hydrological simulations

  • A different development N and S of the

mountains (in the South decrease in the North a small increase in P)

  • Runoff decreases between 5-25 % due to

increased evaporation

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Large scale simulations: precipitation

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Large scale simulations: runoff

Change in annual river runoff between the 1961-1990 baseline period and two future time slices (2020s and 2070s) for the A2 scenarios (Alcamo et al., 2007).

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Considering both:

  • Human impacts: dams, irrigation,…
  • Climate change
  • At the global scale
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Water Stress Changes until 2025

80% of future stress from population & development not climate change! e.g. 85% US global change research funding goes to climate and carbon

(Vörösmarty et al. 2001)

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Role of scale

  • Land use impact may increase with catchment

area (Aral Sea catchment, Nile,…)

  • Climate change impact may decraese with

catchment area (when areas with different climate signals are within the catchment)

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Summary and conclusions

  • In all our data we find both: human impacts and

climate change

  • In many regions the direct human impacts on

water resources are much larger than expected changes

  • For climate change impacts studies a careful

adjustment of RCM data is needed, otherwise…

  • Large uncertainty in RCMs
  • Select different model outputs and different

emission scenarios

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Thank you for your attention