فهرست مطالب heydar zarei

Agricultural water management studies require accurate information on actual evapotranspiration. This information must have sufficient spatial detail to allow analysis on the farm or basin level (Sanchez et al., 2008). The methods used to estimate evapotranspiration are grouped into two main groups, which include direct methods and indirect or computational methods (Alizade and Kamali, 2007). Basics of the indirect methods are based on the relationship between meteorological parameters, which impedes the use of these data with a lack or impairment. On the other hand, this information is a point specific to meteorological stations, and their regional estimates are another problem of uncertainty of their own. To this end, the use of remote sensing technology can be a suitable approach to address these constraints. Real evapotranspiration can be estimated by satellite imagery that has short and long wavelengths and is estimated using surface energy equations (Chihda et al., 2010). Examples of such algorithms include SEBAL (Bastiaanssen et al., 1998 Bastiaanssen, 2000;), METRIC (Allen et al., 2007), SEBS (Su, 2002). Among the above mentioned algorithms, energy billing algorithms have been used (Bagheriharooni et al., 2013; Teixeira et al., 2009). Among the factors of superiority of the SEBAL algorithm, in comparison with other remote sensing algorithms, is a satellite imagery analysis algorithm based on physical principles and uses satellite simulation and requires minimum meteorological information from ground measurements or air models (Bastiaanssen et al., 2002).

Using water resources require the determination of components of the hydrological cycle. Understanding of natural systems and physical laws that manage each component of the hydrological cycle is important for the water resources management. One of the crucial components of the hydrological cycle is evapotranspiration. Most methods that have been presented in this study use point measurements to estimate evapotranspiration. Due to dynamic and changing nature of regional evapotranspiration is not generalizable to the basin, the applied methods are only suitable for the local areas. Technology of satellite remote sensing and remote sensing-based methods can be used for the temporal and spatial estimation of actual evapotranspiration in the small and large basins. Remote sensing data derived from satellite imagery calculates the amount of actual evapotranspiration using surface energy balances model. In this study, actual evapotranspiration at the Bakhtegan-Maharloo basin were estimated and evaluated using Landsat 8 satellite images sensor OLI/TIRS and SEBS energy balance models. The values of evapotranspiration derived from energy balance model and FAO-Penman-Monteith method were compared.The results showed that the evapotranspiration values obtained from the energy balance model has a root mean square error (RMSE) and mean absolute difference (MAD) equal to 0.62 and 0.49 mm/d, respectively, indicating its acceptable performance to estimate the evapotranspiration

Monitoring and evaluation of hydrological drought has become a necessity due to its frequent occurrence in various basins of Iran, and in order to prevent and manage the resulting crisis. In most studies, drought indices have been used to investigate it. Drought indices like Streamflow Drought Index, using statistical calculations on river flow data, ultimately leads to a number that does not have the ability to completely investigate and analyze drought in the studied area. Low flow or minimum river flow is one of the most important drought indices that using different criteria can get a comprehensive understanding of the hydrological drought situation in the region. In most studies, deficit characteristics or low flow frequency analysis have been used. Using different low flow indices is necessary to recognize different aspects of drought and its management. Therefore, the aim of this research was to study hydrological drought of Armand river using all of the low flow indices including flow duration curve, deficit characteristics, low flow frequency analysis and base flow index, which can be used to determine characteristics such as dry and wet periods, amount of flow during drought, drought threshold, duration of drought, volume and intensity deficit and frequency of low flows. Also, in this study, the environmental flow of river was calculated and analyzed.

The Armand River basin with 9961 Km2 area located in Chaharmahal and Bakhtiari province was selected as the study area and the daily flow statistics of the Armand hydrometric station were used from 1957 to 2013. First, by plotting the flow duration curve, three low flow indices Q70, Q90 and Q95 also, the river status including wet, normal and drought periods was determined. Then, the minimum environmental flow was calculated based on the two indices Q75 and Q90, and the deficit characteristics using the threshold level Q70. In order to estimate the return period of low flow series (AM7), a suitable two-parameter gamma distribution function was considered appropriate. Finally, the base flow index was calculated using recursive digital filter method in different time scales.

Based on the results, the Armand River in 28, 22 and 14 years (from 57 years of statistical period) has a flow of less than Q70, Q90 and Q95, respectively (45, 32 and 27 m3/s). Due to the gentle slope of the flow duration curve of basin, also the high value of the BFI index (0.95), it was concluded that groundwater had a high participation in the river flow. The dry period in this river begins when the flow reaches less than 45 m3/s (the threshold level Q70). The results showed that the deficit volume and intensity increased over the past 50 years. Based on the frequency analysis of low flow, in the return periods of 2, 5, 10, 20, 50 and 100 years, the low flow was 34.26, 26.8, 23.1, 21.1, 19.1 and 17 m3/s. Comparison of these values with the minimum environmental flow showed that the river flow becomes less than its minimum environmental flow on average every two years.

Despite the sustained flow in the Armand River (due to the snow-rainy regime of the region, the ability of the basin to save water and drain it during the dry season), the dry periods with different intensities occurred over the past 57 years. Also, the severity of drought has increased due to the increase in the volume deficit of the river in recent years, and if this continues in the future, the severity and frequency of the drought occurrence will increase and the overall flow of the river will decrease.

Drought is a natural phenomenon that occurrence of which has its own laws but the intensification, frequency, occurrence and its repetition depend on the human activities in nature. Destroying water quality, destroying plant cover and soil erosion are the main effects of Drought. In this research in order to investigate the effect of the recent draughts on the groundwater quality, water samples taken from the wells in 3 plains (Ize-peun, Dezful-Andimeshk and Gotvand-Aghili) in Khuzestan province, in two hydrologic years; 2006 (With adequate rainfall) and 2007 (With a significant reduction in rainfall).The parameters under investigation include Ca, Mg, Na, K, HCO3, SO4, EC, TDS and pH. To investigate that if the drought the change in the processes affecting groundwater quality in the plains or not, a non-parametric test Mann–Whitney and Factor Analysis were used. Results showed that although drought year of 2007 didn’t have a significant effect on the groundwater quality of plains, but if the drought continues, water quality may change.