Background: Fire occurrence may lead to a significant impactin many terrestrial ecosystems. This study attempted to evaluate the effects of fire on the water balance components in the Central Zagros, Iran. The study used two modeling frameworks, including WetSpass-M and Bayesian Belief Networks to investigate the effect of fire on the amount of runoff, groundwater recharge and evapotranspiration. The first part of the study was a water balance simulation at a monthly scale. In addition, a Bayesian belief networks was applied to explore and understand key issues affect in the water balance after fire. Calibration and validation of the WetSpass-M model was performed without considering the effect of fire (2000-2014) and then the model was run again to with the fire scenario by reducing manning roughness coefficient and increasing the θ coefficient.
Results: Calibration and validation were performed before finalizing the simulation. A Nash-Sutcliff coefficient of 0.61 and 0.58 was obtained during the calibration and validation respectively. The analysis of the water balance components results depicted that fire has increased the amount of runoff and it has reduced the amount of groundwater recharge and actual evaporation especially in the sparse forest and poor, medium and good rangelands.
Conclusions: Water balance components of each class, i.e. sparse forest, poor, medium and good rangelands were different under fire/non-fire scenarios. The percentage of change in the water balance components were used for comparison. The results of Bayesian model for post-fire scenario showed a significant increase in runoff due to reduced vegetation in the area. Both simulated groundwater recharge and surface flow have showed a reduction rate in the fire occurrence scenario. A similar conclusion was obtained from probabilistic Bayesian model due to reducing vegetation cover and surface changes. Actual evapotranspiration component for the poor rangeland has dropped off significantly. Therefore, there is a need for monitoring hydrologic dynamics of the lands with a high risk of burning.