Modeling based on topographic role on survey and zonation potential evapotranspiration on the geographic information system (case study : Sabzevar township)

Solar energy is the most important effective factor in evapotranspiration that can be change with the amount of any changes in the energy that reached to the ground surface.
The aim of this study is to show the impact of altitude, slope and direction on the amount of estimated ETP in the Sabzevar township.
Results showed that there is 23.34% more ETP in the south compared to the north.
Then, in a GIS environment, the map of DEM was created by using topographic map, and then the ETP map (according to dip direction). This map showed that the most area was occupied by the north face of slopes.
Finally, the main ETP map (according to altitude and dip direction) was made, based on the obtained coefficient at the first step, multiplied to this ETP map. In the last step, by using tables in the GIS environment, the amount of ETP of each pixel on the ETP map multiplied by occupied area, the average of ETP for Sabzevar township was calculated.
This study showed that the amount of ETP by this method is 1164.8 mm.