An analysis of drought events for central plains of Iran through an employment of NOAA-AVHRR data

Document Type: Research Paper

Authors

1 Department of Climatology, Faculty of Geography, University of Tehran, Tehran, Iran

2 Department of Cartography, Faculty of Geography, University of Tehran, Tehran, Iran

Abstract

Drought is a major problematic phenomenon for the mostly semi-arid country of Iran. The north central
regions of Iran (north of Esfahan and Ghom province) have suffered from severe droughts several times during
the last three decades. The frequent occurrence of drought in these regions is due to low and inconsistent
precipitation, abnormally high temperatures, increases in surface albedo and evapotranspiration; especially
during spring. The surface characteristics of Kashan and Ghom regions consist of salty flats and sandy hills
covered by sparse vegetation. The average elevation of the area is 1987 mASL. In the present work, NOAAAVHRR
data have been employed to assess vegetation indices and environmental conditions in the study region
for the years 1998 – 2004; which are then compared to actual ground data such as rainfall, temperature and
relative humidity for a detailed drought analysis. Spatial and temporal variations of meteorological droughts in
Kashan have been analyzed using Standardized Precipitation Index (SPI) at annual and seasonal scales, and have
been generated through GIS based interpolation. Vegetative and thermal drought indices have been calculated
using NDVI, VCI, and TCI values derived from NOAA-AVHRR data. Results from applying remotely sensed
data show that this area is generally of low vegetation index values. The artificial forests and farmlands at the
foothills of the mountains northwest of Kashan region showed relatively high vegetation index values. TCI and
VCI generally show a good relationship with meteorological observations. According to the output of utilization
NDVI and VCI, 2000 and 2001 years were characteristic of drought conditions, while 2002 and 2004 did non
represent drought years. Since TCI index is completely dependent on surface temperature, the combined analysis
of the May and April results were influenced by the low land surface temperatures experienced in April, and
therefore it was very different from the other indices i.e. NDVI and VCI. Therefore thermal IR channels can be
employed used to monitor drought conditions in the semi-arid and arid regions of Iran to assess these regions,
environmental conditions.

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