Hydrologic impacts of cascading reservoirs in the middle and lower Hanjiang River basin under climate variability and land use change

Study region: Middle and lower Hanjiang River (MLHR) basin, China. Study focus: Changes in streamflow are often due to intertwined factors like climatic variability, land use change, and hydraulic constructions, whose relative impact is however poorly understood. In this study, we disentangled these effects by comparing real data and modelled scenarios of catchment behaviour. Modelled scenarios employ the soil and water assessment tool (SWAT), whereas the scenario comparison uses the Indicators of Hydrologic Alteration (IHA). New hydrological insights for the region: Our analyses show that (1) watershed inlet was the major factor altered the streamflow regime at the watershed outlet, which pointed us to consider only the relative catchment contribution in further analyses. (2) Climate variability was the main driver of the net changes in natural hydrological regime, which downplayed the effect of land use change on streamflow variability. (3) The streamflow regulation associated to the progressive increase in reservoirs and their operation significantly altered the flow pattern, causing a general decrease in average streamflow, an attenuation of extreme events indicators, and an alteration of the pulse pattern with more frequent but shorter pulses. (4) The average water withdrawals at MLHR were estimated, which were 8.03 x 10(9) m(3)/year. Overall, this research provides a path to assess the hydrologic impact of cascading reservoirs at the basin level under climate variability and land use change elsewhere.

Automated summary

This study analyzes the hydrological impact of climate variability, land use change, and hydraulic constructions on the streamflow in the middle and lower Hanjiang River basin in China. The results show that watershed inlet is the major factor altering the streamflow regime at the watershed outlet, climate variability is the main driver of net changes in natural hydrological regime, and the increase in reservoirs and their operation significantly alter the flow pattern.