Assessing uncertainties in climate change impact analyses on the river flow regimes in the UK. Part 2: future climate

The first part of this paper demonstrated the existence of bias in GCM-derived precipitation series, downscaled using either a statistical technique (here the Statistical Downscaling Model) or dynamical method (here high resolution Regional Climate Model HadRM3) propagating to river flow estimated by a lumped hydrological model. This paper uses the same models and methods for a future time horizon (2080s) and analyses how significant these projected changes are compared to baseline natural variability in four British catchments. The UKCIP02 scenarios, which are widely used in the UK for climate change impact, are also considered. Results show that GCMs are the largest source of uncertainty in future flows. Uncertainties from downscaling techniques and emission scenarios are of similar magnitude, and generally smaller than GCM uncertainty. For catchments where hydrological modelling uncertainty is smaller than GCM variability for baseline flow, this uncertainty can be ignored for future projections, but might be significant otherwise. Predicted changes are not always significant compared to baseline variability, less than 50% of projections suggesting a significant change in monthly flow. Insignificant changes could occur due to climate variability alone and thus cannot be attributed to climate change, but are often ignored in climate change studies and could lead to misleading conclusions. Existing systematic bias in reproducing current climate does impact future projections and must, therefore, be considered when interpreting results. Changes in river flow variability, important for water management planning, can be easily assessed from simple resampling techniques applied to both baseline and future time horizons. Assessing future climate and its potential implication for river flows is a key challenge facing water resource planners. This two-part paper demonstrates that uncertainty due to hydrological and climate modelling must and can be accounted for to provide sound, scientifically-based advice to decision makers.

[1]  K. Taylor,et al.  An overview of results from the Coupled Model Intercomparison Project , 2003 .

[2]  A. Kitoh,et al.  Future projections of precipitation characteristics in East Asia simulated by the MRI CGCM2 , 2005 .

[3]  M. Webb,et al.  Quantification of modelling uncertainties in a large ensemble of climate change simulations , 2004, Nature.

[4]  L. Hay,et al.  A COMPARISON OF DELTA CHANGE AND DOWNSCALED GCM SCENARIOS FOR THREE MOUNTAINOUS BASINS IN THE UNITED STATES 1 , 2000 .

[5]  Christel Prudhomme,et al.  Uncertainty and climate change impact on the flood regime of small UK catchments , 2003 .

[6]  R. Moore.  The probability-distributed principle and runoff production at point and basin scales , 1985 .

[7]  Valerie Isham,et al.  Simulation and downscaling models for potential evaporation , 2003 .

[8]  T. Wilbanks,et al.  Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change , 2007 .

[9]  A. Young,et al.  Stream flow simulation within UK ungauged catchments using a daily rainfall-runoff model , 2006 .

[10]  N. Arnell,et al.  Adapting to climate change: Public water supply in England and Wales , 2006 .

[11]  Eric Servat,et al.  Study of parameter stability of a lumped hydrologic model in a context of climatic variability , 2003 .

[12]  M. J. Booij,et al.  Impact of climate change on river flooding assessed with different spatial model resolutions , 2005 .

[13]  Keith Beven,et al.  Equifinality, data assimilation, and uncertainty estimation in mechanistic modelling of complex environmental systems using the GLUE methodology , 2001 .

[14]  J. Houghton,et al.  Climate change 2001 : the scientific basis , 2001 .

[15]  D. Cameron,et al.  An application of the UKCIP02 climate change scenarios to flood estimation by continuous simulation for a gauged catchment in the northeast of Scotland, UK (with uncertainty) , 2006 .

[16]  H. Fowler,et al.  Using regional climate model data to simulate historical and future river flows in northwest England , 2007 .

[17]  Dennis Wheeler,et al.  Regional Climates of the British Isles , 2002 .

[18]  Robert L. Wilby,et al.  Uncertainty in water resource model parameters used for climate change impact assessment , 2005 .

[19]  Alexei G. Sankovski,et al.  Special report on emissions scenarios : a special report of Working group III of the Intergovernmental Panel on Climate Change , 2000 .

[20]  M. J. Salinger.  Climate Variability and Change: Past, Present and Future – An Overview , 2005 .

[21]  Nigel W. Arnell,et al.  Effects of IPCC SRES emissions scenarios on river runoff: a global perspective , 2003 .

[22]  Kevin E. Trenberth,et al.  Atmospheric Moisture Residence Times and Cycling: Implications for Rainfall Rates and Climate Change , 1998 .

[23]  Philip B. Duffy,et al.  Uncertainty in projections of streamflow changes due to climate change in California , 2005 .

[24]  Corinne Le Quéré,et al.  Climate Change 2013: The Physical Science Basis , 2013 .

[25]  Leonard A. Smith,et al.  Uncertainty in predictions of the climate response to rising levels of greenhouse gases , 2005, Nature.

[26]  Christian W. Dawson,et al.  SDSM - a decision support tool for the assessment of regional climate change impacts , 2002, Environ. Model. Softw..

[27]  H. Treut.  Les scénarios globaux de changement climatique et leurs incertitudesGlobal scenarios of climate change and associated uncertainties , 2003 .

[28]  N. Arnell.  Climate change and global water resources: SRES emissions and socio-economic scenarios , 2004 .

[29]  Richard G. Jones,et al.  RCM rainfall for UK flood frequency estimation. I. Method and validation , 2006 .

[30]  R. Wilby,et al.  A framework for assessing uncertainties in climate change impacts: Low‐flow scenarios for the River Thames, UK , 2006 .

[31]  J. Palutikof,et al.  Climate change 2007 : impacts, adaptation and vulnerability , 2001 .

[32]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[33]  A J Saul,et al.  Flooding in the future--predicting climate change, risks and responses in urban areas. , 2005, Water science and technology : a journal of the International Association on Water Pollution Research.

[34]  Richard G. Jones,et al.  RCM rainfall for UK flood frequency estimation. II. Climate change results , 2006 .

[35]  M. Rummukainen,et al.  Climate change impacts on runoff in Sweden assessments by global climate models, dynamical downscaling and hydrological modelling , 2001 .

[36]  P. Coulibaly,et al.  Hydrologic impact of climate change in the Saguenay watershed: comparison of downscaling methods and hydrologic models , 2005 .

[37]  D. Stephenson,et al.  Future extreme events in European climate: an exploration of regional climate model projections , 2007 .

[38]  G. Boer,et al.  Warming asymmetry in climate change simulations , 2001 .

[39]  M. Field,et al.  The meteorological office rainfall and evaporation calculation system -- MORECS , 1983 .

[40]  John F. B. Mitchell,et al.  The simulation of SST, sea ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments , 2000 .

[41]  I. Watterson,et al.  Energy and water transport in climates simulated by a general circulation model that includes dynamic sea ice , 1997 .

[42]  G. Cawley,et al.  Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1318 DOWNSCALING HEAVY PRECIPITATION OVER THE UNITED KINGDOM: A COMPARISON OF DYNAMICAL AND STATISTICAL METHODS AND THEIR FUTURE SCENARIOS , 2006 .

[43]  S. B. Jones.  The estimation of catchment average point rainfall profiles , 1983 .

[44]  J. Räisänen,et al.  How reliable are climate models? , 2007 .

[45]  Martijn J. Booij,et al.  Extreme daily precipitation in Western Europe with climate change at appropriate spatial scales , 2002 .

[46]  L. S. Pereira,et al.  Crop evapotranspiration : guidelines for computing crop water requirements , 1998 .

[47]  Nigel W. Arnell,et al.  Relative effects of multi-decadal climatic variability and changes in the mean and variability of climate due to global warming: future streamflows in Britain , 2003 .