Impact Assessment of Climatic Variability on the Streamflows and Predictions for the 21st Century Integrating Global Climate Models

Water management needs to investigate the possible consequences of climate variability on hydrological variables. This paper presents the precipitation and temperature trend patterns and their impact on streamflow (1985-2014) for the Astore basin and streamflow predictions by the year 2100. The trend detection of the two parameters was assessed through the Man-Kendall and Sen’s Slope tests. The climate station data were compared with the results of the trends analysis and reported values of two Global Climate Models (GCMs), BCC-CSM1-1 and GFDL-CM3 (each having Representative Concentration Pathway, RCP 2.6 and RCP 8.5 scenarios). No important trend was noted for the precipitation except an increasing trend in September, while there were rising trends in temperature from December to August, whereas declining trends from September to November, which shows that the summer duration is getting longer while the winter is getting shorter with an early start in September. The results indicated that precipitation trends are reciprocating the temperature. The rising trends in temperature can result in extreme events, floods, and droughts due to extensive glacier melt in the near and far future, respectively. The result of GCMs for the two chosen RCPs had a similar pattern of climatic changes all over the century, with slightly higher values for the RCP 8.5 scenario, experiencing a tendency toward less precipitation and, during some seasons, a modest increase in temperature. The stream-flow predictions using GCMs showed rising trends till the mid-21st century and declining trends by the last decade of the century and even onwards. This rise in summer flows will raise the water level in the Tarbela reservoir located on the downstream of Upper Indus River Basin (UIRB) thus providing excess water for Hydropower generation, increasing till the mid-century and there are also chances of inflows to reservoir, beyond its capacity that can cause flooding to its downstream while after 2091, a continues decrease in water level is expected, which in return, can severely affect the power generation capacity form the reservoir, also causing reducing water supply for agriculture needs.