Impacts of multi-purpose reservoir construction, land-use change and climate change on runoff characteristics in the Poyang Lake basin, China

Abstract Study region The Poyang Lake basin at the Yangtze River, China. Study focus Impacts of multi-purpose reservoirs on runoff are investigated through the lens of spatio-temporal shifts in runoff coefficients (RC) before and after reservoir construction. We furthermore use evapotranspiration (ET) modelling to interpret possible additional impacts of climate change and other ambient changes since the 1950s within the Poyang Lake basin, comprising one of China’s most important freshwater resources. New Hydrological Insights for the Region: Results show that annual average RC and ET remain essentially unchanged despite reservoir constructions and irrigation development. We show that simultaneous, basin-wide implementation of lake-to-land transitions (including wetland drainage) has had a dampening effect on ET, contributing to unexpectedly weak ET trends. Our model furthermore shows that the observed (modest) ET increases since the 1950s can be fully attributed to the warmer climate in the region. Furthermore, the intra-annual distribution of the monthly RC used to be almost identical in all sub-basins during the pre-dam period. We show that the different operation schedules of multi-purpose reservoirs, which reflect location-specific differences in water need over the year, have resulted in pronounced temporal differences in sub-basin runoff characteristics (including RC-values). The present analysis contributes to process understanding, relevant for water management decisions in the Poyang Lake basin and other major multi-purpose dam regions across the world.