ClimateChange Assessment Guide.pdf - University of Waterloo

Estimating Future Local Climates33• High spatial and temporal resolution leads toimproved simulation skill and reduces biases apparentin the GCM;• Many physically consistent climate variables available(Jones and Mearns, 2005);• Improved extreme event simulation for severalvariables (i.e., precipitation, wind speed andtemperature); RCMs can simulate cyclones andhurricanes (Jones and Mearns, 2005);• It is possible to considerfeedback from climatesubsystems such as vegetation, or human impactssuch as land use change;• Better treatment of circulation features and diurnallyvariable convective processes;• Better treatment of the effect of large water bodies(i.e., Great Lakes) (Lofgren, 2004); and• Directly linked to GCM and so climate changes aredirectly transferred to the RCM.The weaknesses of RCMs include:• Multiple scenario, multiple GCM runs for differenttime periods are not readily available;• May be affected by underlying biases in the GCM;• Expensive and computationally complex requiringsignificant resources (i.e., not user friendly, softwarenot available to non-experts);• Shorter simulations are typical, reducing the usefulnessof the output for extreme event analysis; and• Possible inconsistencies between the RCM and theGCM in terms of storm track speed as RCMs do notprovide feedback to GCMs.RCMs compared favourably with statistical downscalingmethods in side-by-side comparisons (Mearns et al.,1999; Wilby et al., 1998) over daily and monthly timeframes for present climate conditions.Of specific interest to this region is the North AmericanRegional Climate Change Assessment Program(NARCCAP). This international program provides highresolution climate scenario needs for North America.RCMs coupled to GCMs are being run in multipleexperiments. Information on the program is available athttp://www.narccap.ucar.edu.Regional Climate Model (CRCM) for the period 2039 to2070 (centred on 2050). Each RCM will be embeddedwithin at least two GCMs and will be run for the SRES A2emission scenario (Table 3.1).These runs will generate output at a 3-hour intervalfor the following meteorological variables relevant tohydrologic modelling:• Specific humidity;• Precipitation;• Air pressure;• Air temperature;• Shortwave radiation;• Zonal surface wind speed; and• Meridional surface wind speed.Once the results of these runs are made available inthe form of meteorological time series, hydrologicalassessments will be possible at a 50 km grid spacing forthe GCM and SRES A2 emission scenario combinations.Some form of uncertainty analysis will also be availableto support these results. While runs are currentlyunderway and one run is archived, the availability of thefinal suite of products is unknown and will be at leastseveral months after the release of this document.While they offer a promising alternative to statisticaldownscaling methods, RCM-based output is notcurrently available in multi-scenario form and istherefore limited in supporting climate change impactassessments. However, when complete, the NARCCAPsimulations will be a valuable resource to assessmultiple RCM scenarios and will support practitionersinvestigating the range of impacts predicted by multiplefuture climates.4.4 Summary of Local Climate Generation TechniquesThe advantages and disadvantages of the five climategeneration methods reviewed in this Guide, includingthe change field method, synthetic and analoguescenarios, statistical downscaling, weather generatorsand regional climate models, are summarized in Table4.1.NARCCAP is currently conducting simulation runs forclimate change. Once complete and archived, theseruns will provide output for future climates over NorthAmerica based upon six RCMs including the Canadian