Why lowland riparian trees are difficult to use for streamflow reconstruction

Existing streamflow reconstructions based on tree-ring analysis mostly rely on species from upland, mainly montane areas, while lowland species (generally plain) areas are rarely used. This limits the understanding of streamflow change history in the lowlands, which is an important basis for water resource management. This study focused on Populus euphratica stands located along the main stream, eastern and western tributaries in the lower reaches of the Heihe River basin (HRb), in arid northwestern China. We investigated how streamflow regulation interferes with riparian trees in lowlands when they used for streamflow reconstruction. Tree-ring width chronologies were developed and analyzed in conjunction with meteorological and hydrologic observation data. The results show streamflow regulation leads in sharp fluctuations in the streamflow allocation between the eastern tributaries and western tributaries. This resulted in instability of the correlation between streamflow at the two tributaries and at the Zhengyixia hydrologic station, with corresponding fluctuations in radial growth of poplar trees on the banks of the two tributaries and at the station. Streamflow regulation altered the natural patterns of seasonal streamflow below the station, changing the time window of poplar response. This study provides useful insight into tree-ring width based streamflow reconstruction in the lowlands.