جستجوی مقالات مرتبط با کلیدواژه « ndvi » در نشریات گروه « مهندسی آب »

The present study aims at investigating the trend and energy complexity of hydro-climatic parameters including discharge, precipitation and temperature and Vegetation Cover (VC) in Zilbierchay catchment, East Azerbaijan, where water table has experienced a sharp drop in recent years. To this end, the water table (over 18 years interval), discharge, precipitation, temperature and VC (over 30 year interval) were examined using Mann-Kendall trend in monthly and yearly scales. The parameters were decomposed using Daubechies mother wavelet (db2) analysis at three 10-intervals and 5 time levels. The results indicated that the reduction of water table and discharge were significant. On the other hand, no significant trend was detected in precipitation and VC, while for temperature, significant increasing trends were observed in most of the months. The result of the complexity analysis revealed that the changes in the complexity of temperature (about 2% increase) were not significant, while the fluctuations reduction was found in precipitation (about 20%). In addition the pattern of fluctuations has changed which affected the complexity reduction of discharge (17%) and depth to the water table (13%). Furthermore, increasing vegetation cover area and temperature through raised evapotranspiration as well as reduced discharge and precipitation in the region have increased the drastic use of groundwater. Therefore, considering the complex relationships and synergistic effects of natural and human factors on water resources together can help managers in optimal and efficient decision making.

Nowadays, in order to reduce the effect of unwanted factors and gather information related to land cover, vegetation indices were used. In this study, the effects of NDVI and VI indices on land cover and runoff curve number of Mansourabad watershed were investigated by using Geographic Information System (GIS) and Remote Sensing (RS). Land cover map was prepared by using vegetation indices and Landsat satellite images. In addition, the results of classification of these two indices and corresponding percentage with surveying data were compared. After that, runoff curve number map was prepared by combining land cover map with land use and soil hydrology group maps and by utilizing SCS table in the GIS environment. To assess the accuracy of each curve number map obtained from each index, runoff peak discharges computed by HEC_HMS model were compared by the measured amounts. The result of the classification showed that NDVI index with Kappa coefficient equal to 0.83 was better than the VI index with Kappa coefficient equal to 0.74 for land cover. These results were verified by lower error percentage between the measured and observed maximum discharge for NDVI index.

Geographic information systems and remote sensing techniques have been increasingly applied in watershed runoff estimation in recent years. In this research, the runoff curve number map of Birjand’s Mansourabad watershed, eastern Iran, was prepared using geographic information system (GIS), landsat images, and the Indian remote sensing (IRS) images based on the factors of hydrologic soil group, land use, land cover, and the hydrologic conditions. The land cover map was determined using Normalized Difference Vegetation Index, (NDVI); the watershed land use map was produced by satellite data; and the hydrologic soil group map was produced using field survey and watershed soil, slope, geology, and land use maps. Results showed that during the period of 2002 to 2006, land coverage density has decreased and consequently the curve number of watershed and its runoff production potential has increased.

Soil moisture and its temporal and spatial variations are one of the critical parameters in climatic, ecological, and hydrological modeling. Overall and consistent views on different parts of an area, repetitive satellite images from inaccessible areas and over large zones, along with regular periodic data are among important outcomes of the Remote Sensing (RS). Rangelands are highly dependent on the availability of water and therefore the vegetation indices can be used for tracking the changes in soil moisture. This study analyzes the correlation between the field measurements of soil moisture obtained using gravimetric sampling and the coincided and lagged MODIS-NDVIs based on the daily meteorological parameters during the growing season (April- August) from 2003 to 2005 in arid and semi arid rangeland in Khorasan Province, north eastern Iran. Results show that the surface soil moisture in these rangelands is moderately correlated to the coincided and lagged NDVI and can be estimated using NDVI during the growing season. Stronger relations can be obtained for surface soil moisture data lagged by 2 weeks with respect to the vegetation index. Considering wind and cumulative evaporation factors represent better temporal and spatial estimation for the surface soil moisture in the study area.