Assessment of the Fire Effect on Water Balance Components Under Different Land Uses, Central Zagros, Iran Case Study

4 Background: Fire occurrence may lead to a significant impactin many terrestrial ecosystems. This 5 study attempted to evaluate the effects of fire on the water balance components in the Central 6 Zagros, Iran. The study used two modeling frameworks, including WetSpass-M and Bayesian 7 Belief Networks to investigate the effect of fire on the amount of runoff, groundwater recharge 8 and evapotranspiration. The first part of the study was a water balance simulation at a monthly 9 scale. In addition, a Bayesian belief networks was applied to explore and understand key issues 10 affect in the water balance after fire. Calibration and validation of the WetSpass-M model was 11 performed without considering the effect of fire (2000-2014) and then the model was run 12 again to with the fire scenario by reducing manning roughness coefficient and increasing the θ 13 coefficient. 14 Results : Calibration and validation were performed before finalizing the simulation. A Nash- 15 Sutcliff coefficient of 0.61 and 0.58 was obtained during the calibration and validation 16 respectively. The analysis of the water balance components results depicted that fire has 17 increased the amount of runoff and it has reduced the amount of groundwater recharge and actual 18 evaporation especially in the sparse forest and poor, medium and good rangelands. 19 Conclusions: Water balance components of each class, i.e. sparse forest, poor, medium and good 20 rangelands were different under fire/non-fire scenarios. The percentage of change in the water 21 balance components were used for comparison. The results of Bayesian model for post-fire 22 scenario showed a significant increase in runoff due to reduced vegetation in the area. Both 23 simulated groundwater recharge and surface flow have showed a reduction rate in the fire 24 occurrence scenario. A similar conclusion was obtained from probabilistic Bayesian model due 25 to reducing vegetation cover and surface changes. Actual evapotranspiration component for the 26 poor rangeland has dropped off significantly. Therefore, there is a need for monitoring 27 hydrologic dynamics of the lands with a high risk of burning.

scenario showed a significant increase in runoff due to reduced vegetation in the area. Both

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Fire is a major negative factor for the most natural ecosystems along with urban excessive 32 development of agricultural lands (Yin et al., 2005). It is also one of the most important physical 33 factors that affect many environmental processes (Thomazet et al., 2014). These impacts mostly 34 lead to changes in land cover and soil characteristics (Shakesby, 2011).In the case of wild fires, 35 they not only reduce the land cover of the natural ecosystems, but also result in damages soil 36 damaged soil due leads to an increased rain droplet exposure. Therefore, it has an important 37 effect on hydrological conditions that are vital to soil loss by increasing hydrophobicity of the  reduced the mineralization of soil carbon in the surface layer, one year after the fire. They also 77 stated the negative effects of fire land cover on soil properties in the first year after the fire were 78 more considerable than the second or third years. 79 The aim of the current studyis to investigate the relationship between fire andsimulated water 80 balance components using the WetSpass-M in the Karebas Basin, a high land located in the 81 Central Zagros geographically. The applied model is a kind of distributed model that calculates 82 the overall water balance for each cell from the independent sub-pixel water budget for each land 83 cover including bare soil, water reservoirs and impermeable land. This means the model takes  The occurrence of the fire phenomenon is a frequent event in the central Zagros region of Iran.

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Similar to other parts of the world, this destructive phenomenon has caused severe after effects to 96 the environment and land cover of natural ecosystems in the region  Chaharmahal-Bakhtiari and Esfahan provinces in the western part of Iran (Fig. 1). The basin is a 106 mountainous region located in the center of the Zagros mountains with an elevation range 107 of1,760 m to 3,794 m.The area west of the basin is mostly mountainous with high altitude and 108 the eastern parts consist of low-slopes and flat areas. The land cover of this study consist of poor rangeland, moderate rangeland, and good rangeland with sparse forests that cover 25, 20, 4, and 110 26 percent of the basin area, respectively. According to the information released by of the Forest, 111 Rangeland and Watershed Organization of the Iran, the canopy density in sparse forests and poor 112 rangeland is 5 to 25 percent while the canopy density in the moderate rangeland varies in rang of 113 25 to 50 percent. For the good rangeland, this value is more than 50 percent.

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Our field investigation indicates that for most fire cases, the cause is due to human factors.

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Previous reports also noted that the impact of human factors could possibly be related to the     the water balance. The first scenario was the modeling of water balance under non-fire 225 conditions, which the model applied using the prepared maps with no consideration of fire and 226 the second scenario was related to water balance modeling considering the occurrence of fire.
Since fire has a significant impact on land surface features, two time series of LAI monthly maps 228 were used, in order to consider the effect of fire on land cover on the base field collected fire/no 229 fire data. The land cover percentage was adopted based on the control and fire areas and      including grasslands, savanna, and croplands. As shown in Fig. 7, the greatest reduction in actual 319 evapotranspiration belongs to poor, moderate, good rangelands and sparse forest. The reason for 320 this sharp change can be related to the type of land cover and its coverage characteristics. In poor rangelands, it may lose the most of vegetal cover and a major reduction in evaporation and 322 interception may be seen after fire occurrence. In contrast, for forest lands, unless the intensity of 323 the fire is extensive due to stronger land cover, remaining materials and renewed coverage 324 increase after fire occurrence. The type of land utilization also has a great impact. For example, 325 poor and medium rangelands are exposed to severe and moderate grazing respectively, whereas 326 in good rangelands, grazing is usually light. This is why the restoration of land cover may be     balance components belongs to the surface runoff 13.5% (Table 4).