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

Abstract

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