An estimation of Thornthwaite monthly water-balance in Mighan sub-basin

Water resources in arid and semi-arid regions are heavily influenced by climate change, water shortage, water regulations, and increased water demands. Monthly discharge is one of the most important factors in hydrological studies. Some of the basins are not equipped with adequate hydrometric equipment. In such a case, average monthly discharge could be estimated by regional monthly water balance models of representative basins. In this study, the following collection of data including: temperature, precipitation and average monthly discharge, and the potential evapotranspiration was calculated by Thornthwaite equations. Remaining parts of water balance equation including: Actual evapotranspiration, soil moisture supply of the area in each month and later months are also estimated via Thornthwaite model. The net water requirements were estimated using the model by assuming that evaporation is the only path for water loss. The results have indicated that timing of recharge is very important in preserving sub-basin hydrology in this region. This modified climate diagram prompts an intuitive understanding of the relationship between recharge and consequent wet spell in Mighan sub-basin of Arak. It may be used as a standard tool to determine adequate water demand in water resources management of the arid regions for wetland protection or restoration.