عنوان مقاله [English]
Jazmurian wetland is located in an endorheic basin at the southern edge of the Dasht-e-Lut. Several factors such as high evaporation, over exploitation of groundwater, dam construction on the rivers feeding the wetland, and the effect of drought and climate changes have caused this wetland to dry out during the recent years. Investigation of dynamic monitoring of water surface area in past and its relation with climatological variation has an important role for reclamation and conservation of wetlands. This study investigated the water body of Jazmurian seasonal wetland from 1972 to 2017 by Landsat satellite images. The temporal monitoring of wetland water area was performed using Landsat Data Series (MSS, TM, ETM+, and OLI). Further, the relationship between wetland water area, rainfall, as well as inflow water the wetland in this period was investigated.
Materials and methods
The meteorological data used included information of 3 evaporation stations for measuring evaporation and 16 rainfall stations for measuring precipitation. Due to lack of hydrometric stations surrounding the wetland, Kahnak Sheybani (Kahn) on Halil River and Bampur (Bamp) on Bampur River were used for measuring inflow water to the wetlands. Note that Kahn and Bamp are about 200 km and 150 km away from the wetland, respectively. In this study Landsat data series (MSS, ETM, ETM+ and OLI/TIRS) between 1987-2017 were downloaded from EarthExplorer. All study regions were within Path/Row 158/41. Geometric and radiometric corrections were done for all used images. After that Normalized difference water index (NDWI) was used to extract water bodies from remotely sensed imagery. NDWI values were derived using combinations of the NIR and green bands as (McFeeters 1996). In this study an appropriate threshold for identifying water features was achieved through trial and error, with comparison to base maps made using visual commentary and field visit. A series of field surveys of water body was done at the same time as the satellite pass occurred using a Garmin GPS device on 9 March 2017, 10 April 2017, and 26 April 2017. Random sample points of the boundary of water body were identified for comparison with the results obtained by NDWI. For visual interpretation of water features, because of strong absorption of near-infrared spectrum by water and strong reflection of vegetation and dry soil. Moreover the relation between wetland water body with climatological variables such as evaporation, precipitation and water inflow to the wetland was determined. Finally in the study period based on data series of observation (60 series) and using SPSS software an equation is presented. That can be used in planning, management and restoration of wetlands
Results and discussion
The near-infrared (NIR) band visual interpretation as well as the optimized threshold value of -0.085 was applied to the NDWI image to discriminate between water and non-water surfaces. A number of control points were used to identify the optimized thresholds for NDWI reclassification in water/non-water. Which showed that the NDWI index has a good performance. Awareness of flooding and the drying trend of the wetland will help in its restoration. If we know which areas of the wetland are drying out earlier and the soil moisture is out of reach sooner, that is to say, they are more susceptible to dust generation. According to field observations, it is clear that the slope is very gentle at the extreme end of the basin. As already mentioned, all the surface water drains towards the wetland. On the other hand, extreme floods in the past have led to considerable sediments moving toward the wetland, where fine-grained sediments have reduced the slope and permeability of the wetlands. In other words, even during a slight precipitation around the wetland, a noticeable surface area of the wetland will become wet and water will appear on the surface of the wetland. Obviously, the vast surface area and the low water level and the high potential of evaporation in the region are not favorable for water to remain on the wetland surface. It also seems that there have been no significant changes in the topography of the eastern part of the wetland, with low rainfall mostly appearing in it. Also the results shows there is a direct relationship between rainfall on the wetland and its water area. On the other hand, rainfall has the maximum effect on the wetland water body. In addition to rainfall, water inflow to the wetland from Halil and Bampour River had an effective role in expanding the water area of the wetland.
Investigation of dynamic monitoring of water surface area in past and its relation with climatological variation has an important role for reclamation and conservation of wetlands. This study investigated the water body of Jazmoriyan seasonal wetland from 1986 to 2017 by Landsat satellite images. Further, the relationship between wetland water area, rainfall, as well as inflow water the wetland in this period was investigated. The results showed in addition to feeding the wetland by Halil and Bempour River, the rainfall around the wetland plays an important role in flood duration of the Jazmurian wetland. Moreover the relation between wetland water body with climatological variables such as evaporation, precipitation and input flow was determined.