Zoning SPI and DI Drought Indices Using Rainfall Network Data in Northwest of Iran

Drought is one of the natural hazards that humans are constantly exposed. Therefore, it is necessary to recognize and analyzed. Drought indices, in fact Indicate the normal limits of droughts occurred during Time period to do possible to evaluate different spatial and temporal scales. Daily precipitation data in a 57-year period (1951-2007) were received. Data in this database is in form of cell 0/25× 0/25 degree arc to the Middle East. To convert the database to a text file (TXT) format, it converted to useable formation MatLab software by programming in Grads software. The next step is the calculation of the indices described in MatLab software. To map the output data, the Surfer and ArcGIS software were used. In this study the data output is seasonal and annual, ultimately standard rainfall index shows the drought rate and has been compared with DI index. Comparison annual maps of deciles Index and the Standardized Precipitation Index shows that the eastern part in Northwest of Iran is Wetter than the western part according to a period of 58 years and The western and central regions of Azerbaijan have drought.