چكيده لاتين :
As a natural phenomenon that characterizes the climate system, drought exerts devastating effects on agricultural
products, including reducing cultivation levels, decreasing crop yield, and changing cropping patterns, thus
threatening the food security of humans and other creatures. Moreover, it brings about some social and
environmental consequences such as threatening human health security, spreading diseases, increasing
malnutrition, increasing the migration of rural residents, influencing the moisture, health, soil erosion, and
vegetation, developing desertification, decreasing the water resources quality, increasing air pollution, and
affecting groundwater reserves, wildlife, and biodiversity. These disastrous effects have turned drought into the
subject of different investigations worldwide. on the other hand, as Iran is located in arid and semi-arid regions
of Asia and suffers from inappropriate rainfall distribution, it faces some problems in terms of cultivating
agricultural lands. Located in eastern Iran, North Khorasan province is not an exception in this regard, being
considered as a region susceptible to different types of droughts, especially agricultural ones, due to its
geographical location. Furthermore, recent droughts in the province have led to reduced water reservoirs'
volume, severe groundwater depletion, reduced discharge of wells' water, damages to rainfed crops, and reduced
irrigated crops in the province. Therefore, this study sought to investigate the relationship between drought and
meteorological conditions in North Khorasan province throughout a 19-year period using remote sensing indices. Materials and Methods: This study used the data collected from synoptic stations in North Khorasan province,
and MODIS imagery data including 16-day MOD13A1 V6 products (500 m spatial resolution) to measure the
NDVI index and 8-day MOD11A2 V6 products (500 m spatial resolution) to measure ground surface
temperature (LST). Extracted from MODIS images in ARC GIS software, a set of remote sensing indices
including NDVI, VCI, LST, VSWI, TCI, VDI, and VHI were also used to monitor the drought. Then, SPI, PNI,
MCZI, and ZSI were measured to investigate the relationship between meteorological and remote sensing
indices. Finally, Pearson correlations were measured between SPI, PNI, MCZI, and ZSI, and VCI, VSWI, TCI,
VDI, and VHI using the SPSS software.
Results: The results of analyzing the Pearson correlation coefficients indicated a strong correlation between SPI,
ZSI and MCZI, and VCI, VHI, VDI, and VSWI in Maneh and Samolghan, Shirvan, Esfarayen, Garmeh, and
Farouj stations, moderate correlations between the indices in Raz, Jirgalan, and Bojnourd stations, and no
significant correlation between the indices in Jajrum station. As for the status of vegetation in North Khorasan
province, it was found that the northern, eastern, northeastern, western, and northwestern parts of the province
had favorable vegetation, while the province's southern, southeastern, and southwestern regions were covered
with sparse vegetation. The results also showed that sparse vegetation played a major role in drought occurrence,
with many of the severe and very severe droughts occurring in the southern part of the province according to the
TCI index, while the north, west, northwest, east, and northeast regions of the province were in the favorable
condition in terms of drought where most of the droughts were of the mild type. Furthermore, based on VCI and
VHI, north, northwest, northeast, east, and west parts of North Khorasan province possessed the highest areas
with mild drought, with the mild drought, persisted during the 19-year period throughout the province, where the
highest area affected by the drought belonged to Shirvan, and Maneh and Samalqan cities in 2000 and 2013,
respectively.
However, most areas in the south, southeast, and southwest of the province were found to have experienced
moderate drought during the study period. According to the VHI (used to displays the combined effects of
vegetation and land temperature surface when monitoring the drought), most areas of the North Khorasan
province were found to be affected by moderate and mild droughts, with merely the southern regions of the
province (Esfarayen and Jajarum counties) experiencing severe droughts. It was also revealed that Farooj,
Shirvan, Bojnord, and Raz and Jorgelan were in favorable conditions in terms of drought, VSWI, and VDI.
However, the south, southeast, and southwest parts of the province were covered by the most drought areas
based on VSWI, and VDI throughout the study period, while normal and optimal conditions were mostly
observed in the north, northwest, northeast, west, and east regions of the province.
Conclusion: It could generally be argued that applying various indicators can provide a better understanding of
the drought situation, as each indicator examines the drought status based on a specific parameter (such as TCI
and VCI) or a combination of several parameters (such as the VHI index). Moreover, evaluation of the
correlation coefficients of indicators could be very effective in providing accurate results, considering the fact
that some satellite-driven indicators such as the meteorological ones have a direct relationship with the drought
status, whose accuracy can better be determined if their relationship with remote sensing indices is investigated.
Therefore, considering this study's results regarding the Pearson correlation coefficients between meteorological
and satellite drought indices, it is recommended that future relevant studies use VCI, VHI, VSWI, and VDI to
monitor the status of drought
