Evaluation of water balance model efficiency using Thornthwaite method in the Arak plain

Evapotranspiration is one of the most important outcomes in the water balance equation for any natural area or water body. It is also a crucial component of the hydrologic cycle. The main purpose in this research was to detect the changes generated in the study region’s water balance for climate impact assessment by using statistical analysis. To reach this purpose, following steps were done. The relationship of temperature-evapotranspiration was obtained using the Thornthwaite method in Arak plain. The parameters including actual evaporation and soil moisture content in this area were estimated using the Thornthwaite model for each month. Remaining parts of water balance equation including: actual evapotranspiration, soil moisture supply of the area in each month and later months were estimated from Thornthwait model. The net water requirements were estimated using the model by assuming that evaporation was the only path for water loss. The results indicated that the timing of recharge was very important in preserving plain hydrology in this region. This modified climate diagram prompts an intuitive understanding of the relationship between recharge and consequent wetness in Arak plain. It may be used as a standard tool for determining adequate water demand in arid regional water resources management that considers wetland protection or restoration.