نوع مقاله : مقاله پژوهشی
نویسندگان
عضو هییت علمی گروه مهندسی آب دانشکده کشاورزی دانشگاه فردوسی مشهد
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Drought is long periods when precipitation falls below normal, and consequently causes shortage of water resources in the affected regions. Drought results in serious economic, social and environmental impacts. Drought is known as a complicated natural hazard, which is very difficult to be understood fully or described Clearly. We tried to clarify the problem by investigating drought patterns and severity during a long period of 31 years (1970-2001), using climatic data for Khorasan province, I.R.Iran. The investigation showed that general changes for dry periods are more or less uniform over the province. We realized that drought (sever or moderate) occurs time and time in the region and actually is a part of the province climate. We also concluded that on average moderate/mild drought has occurred once every two years; while sever/extreme drought occurs once every 6 or 7 years. It should be noticed that drought severity and duration is different as one moves from the south to the central and northern parts of the province. It is, also, clear that droughts recurrences, severities and durations have been increased during recent years. The most sever drought has been occurred during 1970 and 1990. Comparing the index for different months, we concluded that a long duration drought is made of few merged short period droughts with different severities. Finally we realized that Palmer index is a suitable index for drought monitoring, even though there are some criticism, which challenge the index.
کلیدواژهها [English]
)