Setareh Bagheri; Reza Tamartash; Mohammad Jafari; Mohammad Reza Tatian; Arash Malekian
Abstract
Plain ecosystem is highly vulnerable to environmental changes, and drought is the most famous ecosystem change driver that is difficult to identify after its occurrence. In this research, to study the slope of vegetation changes against drought, the NDVI index of MODIS images and the SPI index from 2001 ...
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Plain ecosystem is highly vulnerable to environmental changes, and drought is the most famous ecosystem change driver that is difficult to identify after its occurrence. In this research, to study the slope of vegetation changes against drought, the NDVI index of MODIS images and the SPI index from 2001 to 2016 were used and the map of vegetation changes against drought with five drought stress classes included very low classes, Low, moderate, high and very high, so that a suitable assessment of the drought can be made at specified time scales. The results of slope pattern of spatial change of vegetation against drought showed that across the plain vegetation changes have declined, and from east to west of Qazvin plain, the slope of vegetation changes and land susceptibility to drought have been reduced. So that the most percentage of area in a one-month drought related to the drought class is very low, but in droughts of 3, 6, 9, 12, 24 and 48 months, the highest percent of the area belonged to moderate and high drought classes. The results of this study, the determination of the level of vegetation changes in against drought in the past years and prediction of these changes in the future years, can be used in the planning and optimal use of resources, control changes in the future.
Aliakbar Nazari Samani; Behnaz Zarrin; Shahram Khalighi sigaroudi
Abstract
Rainfall erosivity (RE) energy is an important factor on the soil detachment and transition of them implying an important role on the regional potential region erosion. . In this study SPI index was used in order to determine the climate condition and its consequent effects on RE in Fashand watershed, ...
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Rainfall erosivity (RE) energy is an important factor on the soil detachment and transition of them implying an important role on the regional potential region erosion. . In this study SPI index was used in order to determine the climate condition and its consequent effects on RE in Fashand watershed, Elburz province. At first the drought, wet and normal periods were determined for four rain gage station and then, both EI30 and modified Fournier index (MFI) were calculated at each gauge station. The regression analysis was used to investigate the relationship between EI30, MFI and 24-hour rainfall as well as annual rainfall of data-logging rainfall stations. After that through applying the regression equation the EI30 was extrapolated for eleven typical rain gauges over the different climate periods. The best correlation was obtained between EI30 and annual rainfall (R2 = 0.71). The spatial zonation RE maps were extracted through Geostatistical analysis for drought, wet and normal condition . According to the findings the effects of climate variability on the amount of RE are significant. Maximum and minimum RE are related to the wet and dry period respectively. However the RE on the summer season of dry condition is more than the wet condition and such condition together with low vegetation cover related to the drought condition lead to complicated situation. Despite the popular thought that the low RE can be addressed into the drought condition the rainfall pattern affect the erosivity potential and not the amount of precipitation.
amin salehpour jam; Mohsen Mohseni Saravi; Javad Bazrafshan; Shahram Khalighi
Abstract
Investigation of drought event has a great importance in the natural resources management and planning water resources management. In this research, the effect of the climate change on drought characteristics in northwest of Iran was investigated using the HadCM3 model under A2 scenario. The statistical ...
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Investigation of drought event has a great importance in the natural resources management and planning water resources management. In this research, the effect of the climate change on drought characteristics in northwest of Iran was investigated using the HadCM3 model under A2 scenario. The statistical downscaling was executed using SDSM 4.2.9 and observed daily precipitation, observed predictors and large-scale predictors derived from the HadCM3 model. Afterwards the SPI was calculated for different time scales of 3, 12, 24 and 48 months in the observed period of 1977-2006 and three periods of 2007-2036, 2037-2066 and 2067-2096. Obtained results show that the mean annual precipitation at the stations of Ardebil, Khoy and Oroomieh was decreased in the future periods and it was also increased at the station of Tabriz in the future period. The Ardebil station with the depletion of 97 mm (32 %) in the fourth period than the observed period has maximum rate of the depletion. The results also show that the drought occurrence with more intensity, duration and frequency can occur in the future periods. The comparison of the results between different stations shows that the Ardebil station has the most intensity of dry period in time scales of 3, 12 and 24 months based on the maximum cumulative intensity of dry periods among the stations. On the time scale of 48 months, the Oroomieh station with the cumulative intensity of -92.78, has the most intensity of dry period between the different stations.
