Hydro-meteorological trends in the upper Indus River basin in Pakistan

Abstract

We examined trends in several hydro-meteorological variables in the upper Indus River basin (UIRB) in Pakistan. To represent the diversity of hydro-meteorological conditions in the basin, mean monthly data from 20 meteorological and 8 hydrometric stations were analyzed for detection of trends using the non-parametric Mann-Kendall test in combination with the trend-free pre-whitening approach for correcting time series data sets for serial correlation. Sen's slope method, a non-parametric alternative for estimating a slope for a univariate time series, was used to determine the magnitude of trends. The meteorological variables we considered were: minimum temperature, maximum temperature, and precipitation, whereas the hydrological variable considered was streamflow. For several of the variables, many more trends were identified than can be expected to occur by chance. Analysis of winter maximum temperature revealed an increasing trend with the trend in slopes of 1.79, 1.66, and 1.20°C per 39 yr for the upper, middle, and lower regions, respectively. Precipitation trends were inconsistent and showed no definite pattern. Trends in streamflow were found to be related to increasing trends in mean maximum temperature, particularly in winter and spring seasons. Increased winter temperatures are likely to increase streamflow in winter and spring. During summer months streamflow will decrease and reduce the availability of water in the Tarbela Dam, thereby requiring changes in the reservoir operating policy towards more efficient management of available water. KEY WORDS: Climate change · Trend analysis · Pakistan · Mann-Kendall test · Sen's slope test · Upper Indus River basinResale or republication not permitted without written consent of the publisher Clim Res 46: 103-119, 2011 Many precipitation trend studies have also been carried out in the South Asia region (e.g. Zhang et al. 2005, Huang et al. 2009). Gemmer et al. (2003 showed that there was an increasing precipitation trend in southwestern Xinjiang, which is an area adjacent to the northern part of Pakistan, and in Jammu-Kashmir, which is southwest of Tibet. Archer & Fowler (2004) used linear regression to analyze precipitation data from various stations in the upper part of the Indus River basin with different record lengths. A significant increasing trend of precipitation in winter and summer during the period 1961-1999 was detected. On the contrary, Raziei et al. (2005) concluded that precipitation in Iran is decreasing. Kezer & Matsuyama (2006) investigated runoff trends for the Ili and East Rivers in Central Asia; no statistically significant change was observed except for runoff. Chen et al. (2007Chen et al. ( ) investigated temporal (1951Chen et al. ( -2003 trends in annual and seasonal precipitation, temperature, and runoff in the Hanjiang basin in China using the Mann-Kendall test and linear regression. Results indicated that precipitation did not exhibit a significant trend, but a significant increasing trend for temperature was seen in mo...

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