CR 46:103-119 (2011)  -  DOI: https://doi.org/10.3354/cr00957

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 basin