Climate change and trend detection in selected rivers within the Asia-Pacific region

Global climate change is currently an issue of great concern. This phenomenon was studied using the runoff of large rivers, which can be considered a regional integrator of the local precipitation occurring in their basins. The long-term stationarity and the possibility of trends in streamflow records stored in the databank of the Global Runoff Data Center (GRDC) at the Federal Institute of Hydrology in Koblenz (Germany) were studied. Runoff records originating from. 78 rivers with long monthly runoff series that are geographically distributed throughout the whole Asia-Pacific region were selected for study. For each of the selected rivers, three time series were constructed and analyzed: the mean yearly, and the maximum and minimum monthly discharges. These series were submitted to a two-tier analysis. First, a segmentation procedure developed by Hubert was applied to assess their stationarity. Then the segmented series were submitted to a specialized trend detection software. The results show that about two-thirds of the series have remained stationary and that the monthly minimum runoff exhibited more changing levels (37/78) than the mean (26/78) and maximum (18/78) runoff. Most of the detected changes occurred during the 1960s and 1970s, a period of rapid demographic expansion and urbanization in Asia, when irrigation and other water uses were developed, especially in tropical areas. During the same period and within the area studied, a number of large dams and reservoirs were completed. Since these anthropic interventions could be at the origin of the changes in runoff, there is no regionally consistent evidence supporting global climate change.