ClimateChange Assessment Guide.pdf - University of Waterloo

E-32Guide for Assessment of Hydrological Effects of Climate Change in Ontario32.52mm/6hr1.510.5001/06/204108/06/204115/06/204122/06/204129/06/204106/07/204113/07/204120/07/204127/07/204103/08/204110/08/204117/08/204124/08/2041Figure 5-2: Simulated 6 hour precipitation volumes from CRCM-A2 for June to August, 2041. Application of the change field method to GCM scenario data does not necessitate disaggregation of data. Existingtime series, at appropriate time steps, are simply adjusted to reflect future conditions in this method. It is necessary todisaggregate simulated daily climate data generated using SDSM to hourly time steps.Since HSP-F has been selected as the streamflow model for this study it is convenient to use the WDMUtil tool fordata management (Hummel et al., 2001). HSP-F requires the use of WDMUtil to setup and manage the model inputand output. WDMUtil contains utilities to disaggregate daily data to hourly time step as required by HSP-F in thisstudy. Hourly air temperatures have been generated from the daily maximum and minimum temperatures byassuming that these temperatures occur at established times of the day and that diurnal temperature patterns follow aconstant pattern. Precipitation cannot be disaggregated through any hourly distribution function as this would stronglybias the results. Instead four time series were developed for each SDSM precipitation time series. Daily precipitationwas assumed to fall evenly over 3 hours, 6 hours, 12 hours and 24 hours for four alternate intensities. All four caseshave been applied to the climate change impact assessment. The future local climates generated in this study are summarized in Table 5-2 by totals or averages, as follows:• Current climate (ID 99);• Nine GCM based change field climates (the Percentile Method) with IDs from 9 to 54;• Two GCM based change field climates corresponding to the SDSM applications (IDs 58 and 59), and• Two SDSM generated climates (IDs 60 and 61).