Trend analysis and abrupt change detection of streamflow variations in the lower Tigris River Basin, Iraq

The Tigris River Basin (TRB) is one of the major freshwater resources for Iraq. However, water shortages of the TRB increasingly have become one of the serious problems facing Iraq. The study was carried out to investigate the temporal and spatial variations of the annual and seasonal streamflow and understand the key driving factors for streamflow changes. Therefore, various statistical methods for detecting trends and abrupt changes were applied to long-term streamflow, temperature and precipitation data over the past nine decades along the TRB within Iraq. The findings indicated that: (1) a significant decreasing trend in winter, spring, and summer flows was the major reason leading to a negative annual trend detected in all hydrometric stations; (2) the flow regime of the Tigris River has altered significantly at an annual scale since 1973 (about 40% of the stations) after the construction of large dams in the upstream catchments and (3) the impacts of climate change have been clearly observed in most of the stations since the 1990s, as supported by the increasing trends in all mean temperatures and decreasing trends in approximately 50% of precipitation (p = 0.05). As a conclusion, it can be stated that the reduction in streamflow can be linked mainly to the increased dam construction, reduced precipitation, and increased temperature. The results presented in this study provide a better understanding to help basin managers, hydrologists and policy-makers in making better anthropogenic and climate change mitigation plans in the TRB in Iraq.