River flow trends in the west of Iran during the past 40years: Impact of precipitation variability

• Published in: Global and planetary change 2013-02, Vol.101, p.52-60
• Main Authors: Abghari, Hirad, Tabari, Hossein, Hosseinzadeh Talaee, P.
• Format: Article
• Language: English
• Subjects: Correlation; Hamedan province; Precipitation; Streamflow; Trend analysis
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2012.12.003

A better understanding of hydrological changes associated with climate change can be achieved by analyzing the temporal trends in river discharge time series. We used the non-parametric Spearman's rho, Kendall's tau, Mann–Kendall and Theil–Sen approaches to evaluate annual and monthly trends in river flow data from 12 stations located in the mountainous western regions of Iran over a 40-year period spanning the hydrological years 1969–1970 to 2008–2009. The Pearson correlation analysis was also applied to explore the relationships between precipitation and river flow series. Using a 5% significance level, we found an evidence of downward trends in annual river discharge at Varayeneh, Omar-Abad, Saleh-Abad, Zehtaran and Bahadorbeig stations at the rates of 0.491, 1.00, 0.101, 0.044, and 0.020m3/s per decade, respectively. These significant downward trends started in the hydrological years of 2005–2006, 2000–2001, 2006–2007, 1995–1996 and 1995–1996, respectively. The greatest numbers of stations with significant river discharge trends occur in October and November, accounting for seven and six stations respectively. Annual precipitation exhibited no strong directional trend, although the tendency was toward increasing annual precipitation. Monthly precipitation variability seems to be also increasing for most of the months but no overall trend pattern in monthly precipitation totals emerged. Correlation analyses indicated strong relationships between river discharge and precipitation at the annual scale and for most of the months. ► A downward trend was observed in annual river discharge at 5 out of 12 stations. ► No strong directional trend was obtained for the precipitation time series. ► A strong relationship was found between river discharge and precipitation.