Climate simulations

The simulations with the regional climate model WRF (weather research forecast model) for historical and future climate involves a two-step approach.

First Dynamical Downscaling

The output from the Hadley centers’ HAD-CM3 global climate model for the period 1968-2080 is downscaled to a 35km resolution over North America. The future climate data is generated based on the A2 emission scenario, currently the likeliest scenario for the future. This data is available at a 6-hourly temporal resolution and provides approximately 100 variables including atmospheric and land-surface data. However, this data doesn’t have the appropriate spatial or temporal resolution to be used by the hydrologic model tRIBS. For this reason, a secondary downscaling procedure is needed.

• Status: This first downscaling has been completed for the HAD-CM3 model. The output is stored locally.
• Future work: We have the forcing data fore the second GCM (MPI-ECHAM5), and are currently performing pre-processing to get the data into WRF.

Second Dynamical Downscaling

The secondary downscaling uses the output of the first simulations (6-hry - 35km) as forcing data for WRF, and generates data at a 10km resolution every hour. The area for the secondary downscaling encompasses most of Arizona, western New Mexico and part of northern Mexico (see Figure 1). This domain was selected based on conversations between E. Vivoni, F. Dominguez and E. Rivera. The team has decided not to do continuous simulation but three “time-slice” experiments: 10 years in the past (1991-2000), 10 years in the “near” future (2031-2040) and 10 years in the “far” future (2071-2080).

Figure 1: Domain for secondary downscaling

While there are approximately 100 variables that are available from the secondary downscaling, only a subset are needed for tRIBS. E. Vivoni identified the forcing variables needed by tRIBS, and E. Rivera located them in the WRF output files. These are their corresponding names:

Table 1: tRIBS required forcing variables and their

corresponding names in the WRF output files.

• Status: We have made considerable progress in getting the output from the first dynamical downscaling to the correct format to be input into WRF. We have successfully completed one year of simulation with no problems. It is estimated that each of the 10-year simulations takes approximately 4 days, which makes it feasible to complete the three time slices in 1 month (including all the pre-processing). Each output file contains 13 days (at hourly timestep) and is currently 4GB.
• Future work: We will perform the three time-slice experiments in the coming month.