Moisture index for Iran: Spatial and temporal analyses Hossein Tabari a , P. Hosseinzadeh Talaee b, ⁎ a Department of Irrigation, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran b Young Researchers Club, Hamedan Branch, Islamic Azad University, Hamedan, Iran abstract article info Article history: Received 21 May 2012 Accepted 27 August 2012 Available online 31 August 2012 Keywords: moisture conditions Thornthwaite index precipitation evapotranspiration trend tests Iran Moisture indices, which account the balance between inputs and outputs of water, are typically used to de- termine the moisture conditions and the magnitude of water deficiency in a given area. This work studies the moisture conditions of Iran using the revised Thornthwaite moisture index, a ratio of evapotranspiration to precipitation, over the period of 1966–2005. Long-term trends in the moisture index were assessed by the Mann–Kendall test, the Sen's slope estimator and the Mann–Kendall rank statistic. According to the moisture index, arid and semiarid environmental conditions where the demand for water exceeds the water supply are dominant over the country. The results conclusively show that the significant trends in the moisture index are infrequent and found only at 8 out of the 41 study stations. The significant downward trends of the mois- ture index at Gorgan, Kermanshah, Khorram-Abad, Khoy, Sanandaj, Tabriz and Zanjan stations located in the north, northwest and west regions of Iran began in 1995, 1996, 1996, 1989, 1997, 1988 and 1986, respective- ly. Contrary to that, the significant upward trend at Dezful station started in 1973. © 2012 Elsevier B.V. All rights reserved. 1. Introduction In recent years, there has been a considerable concern about the possibility of climatic changes. Alteration in our climate is governed by a complex system of atmospheric and oceanic processes and their interactions (Rai et al., 2010). It was demonstrated that global surface warming has been taking place at the rate of 0.74 ± 0.18 °C over the period of 1906–2005. Projections by different Atmosphere– Ocean General Circulation Models (AOGCMs) and simpler climate models show that global warming by the end of the 21st century (2090–2099) relative to 1980–1999 can be up to 6.4 °C depending on the emission scenario (IPCC, 2007). With global warming, a change in moisture conditions is predicted in some model scenarios which estimated that drought would persist in some areas (Wang, 2005; Paltineanu et al., 2007; Seager et al., 2007; Gao and Giorgi, 2008). It is projected that these areas will suffer from increased dryness, heat, water shortages, and reduced produc- tion (Schwartz and Randall, 2003). The moisture conditions are a bal- ance between inputs of water (precipitation) and losses of water (evapotranspiration) on land surfaces. The moisture conditions are a limiting factor affecting plant growth and distribution under certain temperature (Zheng, 2000). Owing to the changes of global temperature and precipitation over the earth's land surface, there is a likelihood of changes in the moisture conditions brought about by an intensification of the atmospheric hydrological cycle. Changes of the moisture conditions would influence ecological and agricultural water management, water resource utiliza- tion and desertification adaptation. However, so far there are not so many studies focused on the moisture condition changes as those on temperature and precipitation. This is one main deficiency in the cur- rent climate change research (Wu et al., 2006). Typically, moisture indices are used to determine the moisture conditions and the magnitude of water deficiency in a given area. It can be derived from commonly available data like annual mean tem- perature and annual total precipitation, and thus is suitable for long-term studies (Grundstein, 2009). Basic understanding of mois- ture indices in arid and semiarid regions is essential for proper land management of these lands, in which it is characterized by a severe lack of available water. This has unfavorable effect on their quality and production (Abdulla, 2008). There is a long history of evaluating the moisture conditions through the ratio of precipitation over temperature or evapotranspi- ration (De Martonne, 1926; Thornthwaite, 1948; UNESCO, 1979; UNEP, 1992). Using evapotranspiration parameter instead of temper- ature gives a more realistic estimate of water deficit and would be more representative of climatic variability conditions (Tsakiris and Vangelis, 2004; Khalili et al., 2011). The Thornthwaite moisture index (Thornthwaite and Mather, 1955) is an indicator of the supply of water in an area relative to the demand under prevailing climatic conditions (McCabe and Wolock, 1992). In the index, precipitation is compared with potential evapotranspiration which is a measure of water requirements to determine periods and quantities of water surplus and water deficit. The water deficiency represents the amount by which the precipitation fails to meet the demands of Global and Planetary Change 100 (2013) 11–19 ⁎ Corresponding author. Tel.: +98 911 2528074; fax: +98 811 4227012. E-mail addresses: tabari.ho@gmail.com (H. Tabari), p.hosseinzadeh@iauh.ac.ir (P. Hosseinzadeh Talaee). 0921-8181/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gloplacha.2012.08.010 Contents lists available at SciVerse ScienceDirect Global and Planetary Change journal homepage: www.elsevier.com/locate/gloplacha