The effect of revised topography dataset on improvement of RegCM4 model results (Case study: northern of Iran)

Lack of regional climatic data is great challenge for agroclimatic studies. In this research, the influence topography on RegCM4 model results was investigated. In order of determine the role of topography on improving the results of RegCM model, two topographic datasets (GTOPO, GMTED) were used for a specific period of time and similar conditions to run the model. The experiments were done with lateral boundary conditions obtained from The NCEP-DOE Reanalysis 2 (NNRP2) dataset at 2.5° × 2.5° latitude-longitude horizontal resolution. The sea surface temperature (SST) for the corresponding regional climate simulations were prescribed from the National Oceanic and Atmospheric Administration (NOAA) Optimum Interpolation SST (OISST) dataset with a weekly temporal resolution and 1° × 1° spatial resolution. The topographical output of the model showed an increase of elevation in the Caspian sea coast [max (GMTED-GTOPO) = 254 m], while in some areas of Alborz mountains a decrease in elevation [max (GMTED-GTOPO) = -400 m] was observed. Due to higher elevation of GTOPO in the Alborz Mountains, the derived speed of this simulation is relatively higher than GMTED, which could reach as high as 1.6 m/s during winter season. The highest precipitation difference occurred during spring season in the vicinity of the area where 400 m of decreased elevation was observed, with amounts as high as 16 mm/day (80% increase in precipitation). The temperature differences followed closely the topographical differences. In the seashore areas, where there was increased elevation, temperature decreased correspondingly (max. of -2.4°), whereas in mountainous areas with decrease in elevation, the temperature increase was observed (max. of 1.2°). The findings from this research identified, the modified data (GMTED) is improving the results of the model and should be replace the old data (GTOPO) in future research.