ClimateChange Assessment Guide.pdf - University of Waterloo

Guide for Assessment of Hydrologic Effects of Climate Change in Ontario84Guidance:In scenarios where the daily future GCM outputdata for the study area contains many dayswith small amounts of precipitation and few drydays, the weather generator method should beabandoned.Future daily GCM output will likely overcome theproblem relating to precipitation distribution so that theweather generator can be applied in future studies.6.5.5 Regional Climate ModelThe RCMs are the most promising new technologiesfor estimating future climates with reasonable spatialresolution. Since RCMs are embedded within the GCMs,they are constrained by the GCM and are thereforephysically consistent with the GCM simulations. RCMsincorporate local features and thus, reflect aspects oflocal climate. Furthermore, RCM output is available at 6hour time steps; a significant improvement on daily GCMdata. However, RCM runs are expensive and resourcedemanding and therefore have been applied only to alimited number of SRES scenarios.Guidance:It is recommended that at least one RCM-basedfuture climate be applied in the climate changeimpact assessment to examine the potentialfuture weather variability. The GCM-emissionscenario used in the RCM climate simulationshould, if possible, match one of the scenarioschosen for the suite of GCM-emission scenarios.The DAI site provides RCM output data from theCanadian Regional Climate Model (CRCM). Severalexperiments have been run with versions of this model;however, it is recommended that output from the latestversion of the model, MRCC 4.2.0, be downloadedand applied. This latest version represents the mostadvanced version of the model and most up-to-dateGCM scenarios. Only one option is available at this timefor Ontario as this version of the model has been run foronly the A2 SRES scenario embedded in the CGCM3-4thmember (i.e., Run 4) model run. Output is available forthe 2041 to 2070 time horizon. Additional scenarios arebeing made available and will be possible candidates foradditional runs in the near future.To download the necessary CRCM data, proceed asfollows:• Access the DAI site at http://loki.ouranos.ca./DAI.• Register and login with receipt of an access code.• Select Regional Climate Models on the left handpanel.• Select Canadian Regional Climate Model (CRCM).• CRCM background information and links appear;Select Browse available data.• From the listing of 14 CRCM experiments available,Select experiment “adk” as this is the most recentexperiment using AR4 SRES scenario (A2) with outputfor Ontario (AMNO domain).• Click Next to arrive at the CRCM data screen. SelectLatLon projection.• Select a resolution of 2.5 degrees and set theLatitude and Longitude so that one corner of the 2.5degree grid lies over the study area. This will result ina dataset with data corresponding to each corner ofthe 2.5 X 2.5 degree grid, for four datasets in all. For avery large watershed, it may be desirable to locate thegrid centered over the study area. This will provideRCM data at the four corners of the grid enabling thecreation of up to four climates to represent the studyarea. Resolution of 2.5 degrees results in downloadingthe least data. If resolution is set at 0.5 degrees, forexample, then 36 data sets will be received with datacorresponding to each point in a 6 X 6 grid with 0.5degree spacing between sites.• Set the Lat and Lon according to the area of interest,using degrees easterly for longitude. This means thatnegative degrees from Greenwich are used. Ontariolies in the range -74o to -94o east longitude.• Select the only available start and end dates, 2040-12to 2070-12.• Select the following weather variables:1. FSS - downward solar incident flux at surface inaverage W/m2 over six hours2. PCP - total precipitation rate in mm/s, averagedover 6 hours.3. RHUM (if necessary) - relative humidity as a fractionaveraged over 6 hours.