Effects of climate change and human activities on inflow into the Hoabinh Reservoir in the Red River basin

Abstract Impacts of vegetation change on streamflow have long been an issue for concern and climate variability can also greatly affect streamflow. Climate change refers to the persistent change in climate over long periods of time due to either natural or as a result of human activity. It is very important to quantify the contribution of climate change and human activities on the change of streamflow and provide a scientific basis for future land conservation planning and river ecological conservation. In this study, non-parametric Pettitt mutation method was employed to detect trends and changes in annual streamflow for the period of 1961 to 2008 in the Da River Basin (55000km2), which is the most important tributary of Red River. An upward trend was found in annual streamflow, with an abrupt change identified in 1993 at the Laichau and Tabu stations in the upstream of the Hoa Binh Reservoir. In addition, the Normalized Difference Vegetation Index (NDVI) data from 1981 to 2006 was used to detect vegetation change in the past 26 years. The difference between average annual accumulated NDVI during before and after 1993 and linear slope of annual accumulated NDVI from 1982 to 2006 was calculated. The discharge data was divided into a baseline period (before 1993) and a period of change. Sensitivity-based method and model simulation method were then proposed to separate different effects from climate and human activities. Results indicated that the streamflow is more sensitive to precipitation than potential evaportransportation (PET). Effects of climate variability on streamflow estimated using the sensitivity-based method was weak in the downsream catchment of Tabu station, and strong in the upstream catchment of Laichau station, where the climate effects accounted for about 30% of total streamflow changes. Effects of human activities on streamflow accounted for about 60% both in the Laichau and Tabu catchments. Human activities are the main factor to affect the changes of inflow into the Hoa Binh Reservoir, and climate change also plays an important role.