Climate change effects on groundwater and stream discharge in Denmark

Transcription

1 Climate change effects on groundwater and stream discharge in Denmark Lieke van Roosmalen Dept. of Geography and Geology University of Copenhagen Contributions by: M.B. Butts, B.S.B. Christensen, J.H. Christensen, K.H. Jensen, J.C. Refsgaard, T.O. Sonnenborg.

2 Sensitivity to climate change HOW WILL CLIMATE CHANGE AFFECT HYDROLOGICAL SYSTEMS? Hydrological impact studies can be seen as a sensitivy analysis of hydrology to changes in the climate. Common assumption: other system characteristics remain the same Requires a thorough understanding of the system and a robust representation of the most significant processes? INPUT OUTPUT

3 Non-linear responses Change in mean precipitation Change in the variance of precipitation Arnell, 1997

4 Pyramid of uncertainties Change in mean groundwater head Hydrological model structure and parameterization Downscaling and bias correction method Regional climate model Emissions scenario GCM Uncertainty range

5 Hydrological impact studies Main objective Hydrological model Global change dependent on emissions scenario Downscaling method Climate model data for current climate and scenario Reference time series (observed data) Case study: Denmark What is the effect of climate change on groundwater and stream discharge?

6 Study area Zealand Jutland 5459 km km 2

7 Observed climate ( ) in Denmark Jutland: P ann = 1073 mm, PET ann = 570 mm Zealand: P ann = 762 mm, PET ann = 611 mm

8 Geology study areas Altitude (m) Jutland -100 Sea Quaternary clay Quaternary sand Miocene quartz sand Miocene mica sand Pre-Quaternary clay and silt Altitude (m) 50 0 Zealand Sea Fractured clayey till Quaternary clay Quaternary sandy clay Quaternary sand Limestone and chalk

9 National Water Resource Model MIKE-SHE model code Physically-based, deterministic model Integrated groundwater/ surface water model Grid resolution 500 m Comprehensive 3D groundwater component Distributed recharge

10 Downscaling and bias correction of GCM data Statistical downscaling regression statistical relations between air pressure, circulation, T from GCM and precipitation (weather typing) weather generators delta change method using GCM data Dynamical downscaling Regional Climate Models (RCMs) delta change method using RCM data

11 Regional climate model HadAM3H HIRHAM4 Δx x = 12 km

12 Emissions scenario

13 Observed and RCM precipitation Observed Precipitation Simulated

14 Biases in annual HIRHAM output Temperature bias Precipitation bias (mm) Ref. evapotranspiration bias (mm) 0.6 C 87 mm (13%) 9 mm (2%)

15 Biases in monthly RCM output Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec T ( C) P (mm) ETref (mm) Jacob et al. (2007)

16 Delta change method Climate model output Current Climate Monthly Output delta factor Future P,T,ET Climate Output Hydrological model input Monthly delta factor Observed Future Database Database P,T,ET P,T,ET P Δ ( i, j) = Δ P ( j)* Pobs ( i, j) where Δ P ( j) = P P scen cont ( ( j) j) T Δ ( i, j) = T ( i, j) + Δ ( j) obs T where Δ ( j) = T scen( j) T cont ( j) T

17 Advantages/Disadvantage delta change Advantages: Relatively straightforward method to apply Less sensitive to the quality of the climate model data set Disadvantage: The scenario climate data set is based on an observed data set. Only simple changes in the probability density are taken into account

18 Delta change values for Denmark Scenario Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec. delta change precipitation delta change reference evapotranspiration delta change temperature

19 Meteorological input to hydrological model Precipitation (mm) current J F M A M J J A S O N D Month 120 Temperature ( C) current J F M A M J J A S O N D Month 100 ETref (mm) current J F M A M J J A S O N D Month

20 Spatial distribution seasonal delta change values precipitation DJF MAM JJA SON Delta change value

21 Example delta change values Delta change values for precipitation for Denmark and for Stor Å sub-catchment J F M A M J J A S O N D Whole DK Subcatch ment Internal variability or robust climate change signal?

22 Does the higher horizontal resolution of the RCM have an effect? Delta change value Precipitation 50 km HS1 50 km HS4 25 km 12 km J F M A M J J A S O N D Month

23 Comparison with other RCMs 1.6 Precipitation 4.8 Temperature Delta change value Delta change value J F M A M J J A S O N D Month 2.0 J F M A M J J A S O N D Month Mean HIRHAM-50km PROMES REMO CLM RegCM RACMO RCAO CHRM

24 Annual climate input 695 (14%) 725 (19%) (14%) 677 (19%) 570 ET ref (mm) 10.8 (2.2) 11.7 (3.1) (2.3) 11.4 (3.2) 8.2 T ( C) 872 (14%) 833 (9%) (16%) 1202 (12%) 1073 P (mm) Present climate Present climate Zealand Jutland

25 Recharge Mean annual recharge (mm) Present Jutland (13%) 708 (22%) Zealand (14%) 366 (27%) 6,0 5,0 Jylland Recharge (mm/day) 4,0 3,0 2,0 1,0 0,0-1,0 Present J F M A M J J A S O N D Month

26 Groundwater head - Jutland Change in mean annual groundwater head in primary aquifer (m) Change in head (m)

27 Groundwater head - Zealand Change in mean annual groundwater head in primary aquifer (m) Change in head (m) Change insignificant compared to ME of 0.53 m

28 Change in groundwater recharge

29 Stream discharge - Zealand discharge (m3/s) Sjaelland station current J F M A M J J A S O N D month relative change (%) Sjaelland station J F M A M J J A S O N D month

30 Effects on irrigation in Jutland Current Irrigation (10 6 m 3 ) (91%) 79 (50%) Irrigation (10 6 m 3 ) 6 m 3 ) Mean annual irrigation Year current Irrigation (mm) Mean monthly irrigation current climate scenario scenario May Jun Jul Aug Sep Oct Month

31 Current work: direct use of RCM data in hydrological model Threshold correction and scaling approach normalized precipitation (-) RCM observed precipitation bin (mm/day)

32 Thanks for your attention! Contact information: Lieke van Roosmalen Department for Geography and Geology, University of Copenhagen Øster Voldgade Copenhagen K Denmark tel. nr: lvr@geo.ku.dk