Jordan Journal of Civil Engineering, Volume 2, No. 3, 2008 - 228 - Severity of Droughts in Arid Regions Zeyad S. Tarawneh 1) , Elgaali A. Elgaali 2) and Moshrik R. Hamdi 3) 1) Department of Civil Engineering, The Hashemite University, P.O. Box 150459, Zarqa 13115, Jordan. E-mail: zeyadt@hu.edu.jo (author for correspondence) 2) Civil Engineering Department, Higher Colleges of Technology, Dubai Men's College, P.O. Box 15825, Dubai, United Arab Emirates. E-mail: eelgaali@hct.ac.ae 3) Department of Land Management and Environment, Faculty of Natural Resources and Environment, The Hashemite University, P.O. Box 150459, Zarqa 13115, Jordan. E-mail: moshrik@hu.edu.jo ABSTRACT The increasing water shortage in Jordan threatens the environment and badly affects most of the scoi-economic activities. In central Jordan, where major agricultural and water storage projects are located, the October – May rainy season precipitation for two gauging sites; namely Amman Airport and Madaba, is used in the present study to investigate the occurrence of extreme droughts. The extreme regional dry year occurs when the precipitation in that year falls under the threshold of 1 Standard Deviation below the long-term mean at site. Historical precipitation data, 1938 – 2005, are used to simulate 50000 precipitation data using multivariate stochastic simulation model of order 1, MAR(1). Drought analysis using the historical precipitation shows that extreme droughts fall out as individual years, while using generated precipitation droughts is distributed as 1 year events mostly, and as 2 and 3 years duration although less. This study also presents a theoretical model to estimate the return period of extreme droughts. The estimated return period of the 1 year extreme drought in central Jordan is around 10 years, whereas it is 160 years or more for droughts of longer durations. The probability that an extreme drought occurs at least once in a planning period of 25 years, defined as the risk, is found to be more than 90% for drought of 1 year duration, while it is found to be 15% or less for events of 2 years or more. KEYWORDS: Drought analysis, Precipitation in Jordan, Return period, Stochastic simulation. INTRODUCTION Jordan's climate is generally characterized by tremendous temporal and spatial variations. The geographical position of Jordan as an eastern Mediterranean region mainly governs the time variation, while the spatial variation is attributed to discrepancy in elevations that range from 416m below the mean sea level at the Dead Sea to 1800m above the mean sea level in the southern Highlands. In Jordan, the three main climatic zones are: the Jordan Rift Valley, the northern and southern highlands, and the eastern and southern deserts (MWI, 2004). The Jordan Rift Valley is characterized by its sub-tropical climate, mild winters and very hot summers, with an annual rainfall ranging from 350mm (northern part) to less than 50mm in the south towards the Red Sea. In the northern and southern highlands, mainly cool rainy winters and warm summers are dominant seasons having some regions receive around 600mm of rainfall in an average year. The eastern and Accepted for Publication on 1/7/2008. © 2008 JUST. All Rights Reserved.