Modeling Plants Yield Based on Climatic Factors and Drought Indices in Selected Sites of the Provinces of Markazi and Qom in Iran

Prediction of precise forage production and proper management strategies requires identifying key climatic factors in different regions. The objective of this research is to compare forage production in different region based on climatic factors and drought indices. The study sites include Arak، Roudshore، Baghic، and Gharahso in Central and Qom provinces. Climatic factors and drought indices include precipitation، temperature، evapotranspiration، standardized precipitation index (SPI)، and Reconnaissance Drought Index (RDI). For each climatic variable/or indices، 33 time periods of 1، 2، 3، 4، 6، and 9-month were specified. We have used Principle Component Analysis to decline the number of variables and then، the appropriate time periods were selected. By using stepwise and best subset، the relationship between forage production and each of the climate factors and indices was modeled. To select model، assessment statistics of R، MBE، RMSE، MARE، and IPE were used. Finally، to predict forage production in Roudshore، Baghic، and Gharahso sites، models based on evapotranspiration (RMSE=7. 7، r=0. 99)، RDI (RMSE=3. 1، r=0. 99) and precipitation (RMSE=4. 0، r=0. 99) were selected respectively. The best model was based on the combinations of climatic factors and drought indices (RMSE=0. 2، r=0. 99) for Arak. In general، the relation between forage production and drought condition based on RDI is stronger than its relationship with precipitation and temperature. As we have used precipitation and evapotranspiration simultaneously in RDI، so this index is more precise than SPI.