Theor Appl Climatol (2015) 119:443–464 DOI 10.1007/s00704-014-1120-4 ORIGINAL PAPER Identification of trends in hydrological and climatic variables in Urmia Lake basin, Iran Farshad Fathian & Saeed Morid & Ercan Kahya Received: 2 August 2013 /Accepted: 1 February 2014 /Published online: 4 March 2014 # Springer-Verlag Wien 2014 Abstract The drawdown trend of the water level in Urmia the streamflow in Urmia Lake basin is more sensitive to Lake poses a serious problem for northwestern Iran which has changes in temperature than precipitation. In general, the had negative impacts on agriculture and industry. This re- decline in the lake water level can be related to both the search investigated likely causes of the predicament by esti- increase of temperature in the basin and an improvement in mating trends in the time series of hydroclimatic variables of over-exploitation of the water resources. the basin. Three non-parametric statistical tests, the Mann– Kendall, Spearman rho, and Sen’s T, were applied to estimate the trends in the annual and seasonal time series of tempera- 1 Introduction ture, precipitation, and streamflow at 95 stations throughout the basin. The Theil–Sen method was also used to estimate the Urmia Lake has been shrinking for the last 15 years, and its slopes of trend lines of annual time series. The results showed area has decreased from 6,100 to 4,750 km2 (Jalili 2010) a significant increasing trend of temperature throughout the resulting in about 6 m drawdown in water level. The decline basin and an area-specific precipitation trend. The tests also of the water lake has jeopardized the region’sindustrialand confirmed a general decreasing trend in the basin streamflow agricultural sectors. Furthermore, the decrease in water level that was more pronounced in the downstream stations. The of the once vibrant and vivid lake has led to buried-underwater annual trend line slope was found to be from 0.02 to 0.14 °C/ salt exposure. Persistence of this situation allows the exposed year, −7.5 to 3.8 mm/year, and −0.01 to −0.4 m3/s/year for salt to blow away, causing a serious threat to the health of the temperature, precipitation, and streamflow, respectively. The inhabitants of the region. Various reasons have been stated as homogeneity of the monthly trends was also evaluated using the major causes of this predicament, including changes in the Van Belle and Hughes tests as confirmation. Temporal hydroclimatic variables, human activities (development of analyses of the trends for the temperature and streamflow of agricultural lands due to increasing water diversion for irrigat- the basin detected significant increasing trends beginning in ed agriculture), and mismanagement (Eimanifar and Mohebbi the mid-1980s and 1990s. The correlations between 2007; Golabian 2011; Zarghami 2011; Hassanzadeh et al. streamflow and climate variables (temperature and precipita- 2012). Thus, a trend analysis of rivers’ inflows to the lake is tion) were detected by Pearson’s test. The results showed that a first step to investigate the plausible causes. However, the existence of an increasing or decreasing trend in a hydrologic F. Fathian (*) time series can also be explained by changes in precipitation Department of Water Resources Engineering, Tarbiat Modares and temperature as two of the most effective meteorological University, Box: 14115-139, Tehran, Iran drivers in rainfall–runoff processes. e-mail: [email protected] A number of statistical techniques have been used to iden- S. Morid tify significant trends in climate variables using either para- Department of Water Resources Engineering, Tarbiat Modares metric or non-parametric tests (e.g., Kahya and Kalaycı 2004; University, Box: 14115-139, Tehran, Iran Partal and Kahya 2006; Bandyopadhyay et al. 2009; Pal and Al-Tabbaa 2011; Tabari et al. 2012; Kumar et al. 2009; Zhao E. Kahya Hydraulics Division, Civil Engineering Department, Istanbul et al. 2010;Shahid2011). The former trend tests are more Technical University, Maslak, 34469 Istanbul, Turkey powerful than the latter ones; however, they require data to be 444 F. Fathian et al. independent and normally distributed. In contrast, the non- the temporal trend of annual precipitation trends in ULB. parametric trend tests only require the data to be indepen- Their results showed extreme fluctuations in annual precipi- dent and can tolerate outliers of the data (Huth and Pokorná tation during 39 years so that this trend is decreasing in most 2004; Zhang et al. 2006;Chenetal.2007). The Mann– stations over basin. Katiraei et al. (2006) and Rezaei Kendall (MK), Spearman’s rho (SR), and Sen’s T (ST) tests Banafsheh et al. (2010) focused on daily precipitation. They are typical examples of some non-parametric techniques. applied the MK test for the period 1960 to 2001 and found Moreover, the Van Bell and Hughes (VH) test used to similar results about precipitation trend in the basin. Their detect the homogeneity of seasonal trends has been used results showed that most stations located in the ULB have in few studies (Kahya and Kalaycı 2004; Dinpashoh et al. decreasing precipitation trend. In another study, Jalili (2010) 2011; Jhajharia et al. 2012). also used the MK test and reported no trend in the precipita- In Urmia Lake basin (ULB), previous studies have not tion time series of synoptic stations in the basin for the period much concentrated on climate variables, except those 1990 to 2005 as increasing temperature trends at most with focus on temperature and precipitation. Streamflow, stations. as the most important data are used in planning and The objective of present study is to explore temporal designing water resources projects, has received less monotonic trends in the time series of temperature, precip- attention. Thus, there is an obvious need for more re- itation, and streamflow in the ULB using three non- search in this area to provide an integrated prospective parametric statistical techniques, namely the Mann–Ken- about status of streamflow, and no study has yet been dall, Spearman rho, and Sen’s T tests. Trends in one or both exclusively conducted for streamflow trend in Iran, es- of these variables could be seen as potential evidence of pecially in ULB. climate change and its impact on the hydrologic cycle, Large body of research throughout the world has involved which could eventually lead to shifts in the availability of trend analysis of hydrological and climatic variables with water across the ULB. In order to locate the beginning important indications of climate change. In this context, a year(s) of a trend and estimate the slope of trend, we review of the literature showed that temperature is increasing adopted two respective tests: the sequential Mann–Kendall throughout the world (Stafford et al. 2000; Brunetti et al. (SMK) and Theil–Sen (TS). Moreover, the Van Belle and 2000; Yue and Hashino 2003;Feidasetal.2004;Wuetal. Hughes homogeneity test is used to check the homogeneity 2007;Zhaoetal.2010; Fan and Wang 2011), that is, a fact of trends. emphasized by the Intergovernmental Panel for Climate Change (IPCC 2001). However, it is not the case for precip- itation as their results have not appeared to be consistent to 2 Data and methodology those of temperature (Zhang et al. 2000;Staffordetal.2000; Partal and Kahya 2006; Kumar et al. 2009; Pal and Al-Tabbaa 2.1 Study area and data 2011; Fan and Wang 2011). The analysis results showed that there are different results of precipitation trends depending on The ULB is located in northwest Iran and covers an area of the region of the study. For example, decreasing trends of 51,800 km2 (Fig. 1). It is the largest lake in the country and is annual and seasonal rainfall were noted in Italy (Brunetti et al. also one of the world’s saltiest bodies of water. The lake basin 2000), India (Duan et al. 2006;PalandAl-Tabbaa2011), Sir includes 14 main subbasins that surround the lake with the Lanka (Zubair et al. 2008), southeastern Australia (Murphy areas that vary from 431 to 11,759 km2. The most important and Timbal 2008), and Turkey (Partal and Kucuk 2006). On rivers are ZarrinehRoud, SiminehRoud, and Aji Chai. Numer- the other hand, increasing rainfall trends were found in ous hydrometeorological stations exist in the basin; because Spain (Mosmann et al. 2004), the USA (Groisman et al. some had short record lengths, not all were applicable. The 2001), and Canada (Zhang et al. 2000). Trend analysis for selected stations are shown in Fig. 1.Theycomprise35rain streamflow is more complicated, since it is affected by gauge stations, 35 stream gauge stations, and 25 temperature climate variables as well as land processes. Streamflow gauge stations (Table 1). The gauging stations selected for trends have been extensively analyzed in different parts analysis were based on a large record of data (>30 years) for of the world to document long-term hydrologic trends and validity of the time series and trend analysis results and possible effect of climate change on hydrology. Studies continuity of their records as evenly distributed throughout include both analyzing trends at catchment (Zhang et al. the basin as possible (Githui 2009). All records started from 2006; Masih et al. 2010;Zhaoetal.2010) and national 1950s, 1960s, and 1970s and ended on with the year 2007 for scale (Lettenmaier et al. 1994; Kahya and Kalaycı 2004; all analysis. Stations were selected having records with min- Kumar et al. 2009). imum continuous 30 years of observations. In addition, data Specifically, Jahanbakhsh-Asl and Ghavidel Rahimi recorded annually from 1966 to 2008 of the lake level at (2003) used the linear and polynomial regressions to analyze Golmankhaneh station was also prepared and applied for Identification of trends in hydrological and climatic variables 445 Fig.