چکیده:
Drought is a major environmental disaster in many parts of the world. Knowledge about the timing, severity and extent of drought can aid planning and decision-making. Drought indices derived from in-situ meteorological data have coarse spatial and temporal resolutions, thus, obtaining a real-time drought condition over a large area is difficult. This study used advanced very high resolution radiometer (AVHRR) images to evaluate the efficacy of NOAA-AVHRR data for monitoring drought in Iran for the 1997-2005 (March-July) time period. Ten-day maximum normalized difference
vegetation index (NDVI) maps were produced and a vegetation condition index (VCI), vegetation health index (VHI) and temperature condition index (TCI) for the same period was calculated. Precipitation data from 47 synoptic meteorological stations was collected to calculate the standardized precipitation index (SPI) as a meteorological drought index. Analysis and interpretation of these maps revealed that the spatial extent of the satellite-derived drought-indices and SPI generally confirm each other. Based on the statistical analysis, higher correlations were found among the satellite-derived indices while lesser or no relationships were found between the satellite-derived indices and SPI. The results revealed that high correlations were found among TCI and VHI, VCI and VHI in dry, normal, and wet years (0.662 to 0.813). Iran suffered
from severe drought during 1999-2001.The results of remotely-sensed indices and the SPI index for 2002-2005 most of the region show that it experienced normal conditions.
خلاصه ماشینی:
This study used advanced very high resolution radiometer (AVHRR) images to evaluate the efficacy of NOAA-AVHRR data for monitoring drought in Iran for the 1997-2005 (March-July) time period.
The results of remotely-sensed indices and the SPI index for 2002-2005 most of the region show that it experienced normal conditions.
For more than a decade, remote-sensing techniques have been used to identify and monitor drought-affected areas on regional, national, and global scales with satisfactory results (Tucker and Choudhury, 1987; Kogan, 1997).
Drought in different regions of Spain during 1987-2001 was evaluated using remote sensing data with good results (Gonzalez et al.
These indices are derived from climatic data such as precipitation thatis frequently scattered or insufficient and unavailable for timely drought detection, monitoring and decision-making (Unganai and Kogan, 1998).
(2006) studied drought conditions by comparing seven drought indices (Deciles index, percent of normal, standardized precipitation index (SPI), China-Z index (CZI), modified CZI, Z-score, and effective drought index (EDI)) in Tehran province, Iran.
The present study compared different remotely- sensed indices with a meteorological index (SPI) for meteorological drought monitoring from 1997 to 2005 across Iran.
, 1998; Malingreau and Belward, 1992; Marsh et al.
Several studies have found that the NDVI can facilitate observance of drought in time series satellite data and provide further analysis of the relationships between rainfall, soil water conditions, and the NDVI (Kogan, 1990; Di et al.
The results of remotely-sensed and SPI indices for the years 2002 to 2005 showed thatmost of the region experienced normal conditions.