جستجوی مقالات مرتبط با کلیدواژه "lag time" در نشریات گروه "آبخیزداری، بیابان، محیط زیست، مرتع"

One of the resources that have been severely affected by drought is groundwater, however it has been considered less than other water resources. Due to the recent droughts especially in the central regions of Iran, investigating the impact of droughts on water resources is very important. The main aims of this study are characterization of meteorological and hydrogeological droughts, assessment the effects of drought on groundwater level fluctuations and determining the critical regions of Shahrekord Plain Aquifer. For this purpose, modified Standardized Precipitation Index (SPImod) and Groundwater Resource Index (GRI) were used to assess meteorological and groundwater droughts, respectively. Also, the cross-correlation test was used to investigate the relationship between the meteorological drought and the groundwater drought. In this research, the monthly precipitation data of Shahrekord synoptic station and monthly groundwater level data of 35 piezometers in this plain in the period of 1984-2015 were used. Based on the result of GRI index, Shahrekord Aquifer was divided into three regions which cover the north and northwest, central and south-east and southwest. The results of correlation between modified SPI in various time scales of 1, 3, 6, 9, 12, 18, 24 and 48 months and GRI index indicates the highest correlation between 18-month modified SPI and GRI. The results also showed that the effect of meteorological drought on GRI index appears with 6 and 18-month delay on northern and central areas, respectively, and without delay on the South West of the Shahrekord Aquifer.

Long meteorological drought can lead to the onset of hydrological drought. In this research, the lag time between the two types of drought was investigated for determining the hydrologic drought onset after realizing the climatological drought. This is a matter to provide managers with enough time for decision making before the occurrence of water shortage in the watershed. The SWAT water balance model was used to determine and predict the lag time between the two types of drought for Foomanat (Anzali wetland) watershed in Gilan province Due to the ability to simulate the long-term flow of representative rivers in the basin. The OAT method was employed for the sensitivity analysis of the water balance model. Among the parameters used in SWAT, three parameters including curve number, available water, and the evaporation compensation factor in the soil were recognized as the most effective parameters for the results of the model. Calibration and validation of SWAT were performed using SCH model. The calculated Nash-Sutcliff and correlation coefficient in estimating runoff as well as determining and predicting the lag time between the two types of drought by SWAT were acceptable. The Nash coefficient was obtained as 0.68 and 0.8 for calibration, and 0.65 and 0.79 for validation periods, respectively. Using the calibrated model, one can predict the water balance situation and the lag time between the onset of meteorological drought and the emerging hydrological drought in the watershed for any interested meteorological drought scenarios. Based on the results, the chance of having a one -month lag time, is more than 70 percent, while the chance of a 2-month lag time in the Foomanat watershed Anzali wetland) is more than 23 percent.

Estimation of floods in a basin with various return periods is one of the effective management strategies for reducing flood damage. One of the methods for estimating flood discharge is to make synthetic unit hydrograph using the physical characteristics of the basin. The more accurate inputs of the model, the more validated results. Hence, in basins in which Instantaneous peak discharge is recorded, by comparing observed flood discharge values and modeled values by synthetic unit hydrograph, the physiographic parameters of an area can be optimized to the extent possible and accurate information can be obtained. In this study, by using the recorded data at the hydrometric station, the runoff coefficient and the lag time were calibrated by loss method and routing method of SCS unit hydrograph in the HEC-HMS software and then Flood has been modeled with different return periods, so that, the results in all the return periods have had a Nash-Sutcliff coefficient higher than 0.9 and RMSE lower than 0.5 which indicates appropriate optimization of the model. Also, the runoff coefficient and concentration time were optimized based on model calibration, which could be effective in water resource planning and soil characteristics of a watershed such as permeability.

Monitoring of Meteorological and groundwater droughts and determining of the lag time between these two types of droughts in spatial various locations can help in consumption management and protection of the groundwater resources. In this study, spatial and temporal changes of droughts were analyzed using the Standard Precipitation and Groundwater Resource Indices (SPI & GRI) in the northern Mahyar plain located in Esfahan province. The results showed that groundwater drought in most areas of the aquifer have occurred with a longer lag time (48 months). This is due to increase of groundwater depth and probably due to decrease permeability and blocking pores of the alluvium formations as a result of high number of exploitation wells and heavy withdrawal of groundwater resources in the area. In the western part of the aquifer, particularly around the Ajrakh piezometer, there were high correlations between meteorological and groundwater droughts in lag time of 24 months with R2 value of 0.62. In this part of the aquifer, the factors that make relatively fast response of groundwater level to precipitation fluctuations were the high permeability coefficient, input flows from the adjacent aquifer, lateral recharge caused by permeable limestone formations close to the plain, keeping of aquifer effective porosity and control of subsidence phenomenon due to transferred water from Mahyar channel. Also, the results of spatial mapping of meteorological and groundwater droughts showed increase in the amount of lag time between meteorological and groundwater droughts and expansion of drought severity in most parts of the aquifer over time.

Analysis of drought and factors affecting it using remote sensing data has a high potential to improve scientific knowledge about the properties of drought and the effects of this phenomenon on vegetation. The present study was aimed to investigate the relationship between satellite indices and the SPI index in northern rangeland of Golestan province. For this purpose, SPI index in one, three, and six month- moving averages was calculated and then zoning maps were prepared using kriging. Then, using MODIS images and the corrections, required for this type of sensor, made on the images, a vegetation map was prepared using the indices of NDVI, SAVI and VCI. In order to synchronize the climate data with satellite images, a 9 -year-old common time base was selected. Finally, in order to investigate the relationship between vegetation indices with the SPI indices correlation coefficient and linear regression were used. The results indicated a good correlation between satellite indices and SPI indices in the peak months of vegetation growth. In addition, correlation between vegetation cover indices and three and six-month moving average in non-growing season, and with a one-month moving average of SPI in growing season was higher.

Drought is the most hazardous natural phenomenon. Although not preventable, its negative effects can be reduced through taking some measures. One of the systems severely affected by drought while less considered is the groundwater. In this study, drought status and its impact on groundwater resources was investigated in Alashtar Plain using Standardized Precipitation Index (SPI) at monthly, quarterly, and annual scales and the Groundwater Resource Index (GRI) during the statistical period of 1991-2010. After data collection, statistical errors were corrected by subtraction and ratios method. Then, to determine the status, SPI and GRI were calculated with DIP software on an annual, seasonal, and three, six, nine, 12, 18, 24, and 48-month time scales for Alashtar Plain. Then, according to SPI and GRI value, the moisture status were determined for each period. Results indicated that the trend of plain meteorological and groundwater drought is negative. Correlation between SPI at different time scales with and without the time delay and with average groundwater level and GRI was analyzed. Statistical analysis showed that SPI was significant at the level of 0.01, in the 24-month time scale without any time delay with mean groundwater level and GRI and had the highest correlation coefficient, suggesting the impact of drought on Alashtar plain groundwater. Regression relation between the mean level of the water table and SPI_24 showed that 64.4% of the variance at the mean level of water table was affected by SPI_24 and 35.6% was affected by other factors. Drought magnitude (DM) analysis showed that meteorological and groundwater droughts are consistent with winter and autumn, respectively. Undoubtedly, optimized utilization management, especially in spring and summer, may have a critical impact on preventing damages to the groundwater resources of the region.