Spatiotemporal distribution patterns and impact factors of baseflow for headwater catchments in Zhejiang Province

Baseflow from headwater catchments plays a critical role in connecting terrestrial systems with downstream rivers, lakes and other aquatic environments. However, baseflow processes in headwater regions are challenging to observe and predict, and their spatiotemporal distribution laws remain the least understood so far, which limits the management of stream protection, river ecological water demand, and social water demand. In this study, 25 headwater catchments in Zhejiang Province were selected as the study areas. The time series of baseflow were obtained through digital filtering method for investigations of the spatiotemporal distribution law of baseflow among different catchments and the controlling mechanism. The results show that the Baseflow Index (BFI) is generally lower during wet months with abundant precipitation and quick flow, but higher during dry seasons. The monthly proportion of baseflow and BFI are positively correlated and negatively correlated with the monthly proportion of runoff and precipitation, respectively. The study found that surface morphology includes average elevation, average slope, curvature and basin length was significantly correlated with BFI. Specifically, higher elevation and steeper slopes are associated with greater BFI values during the flood season. We also found that due to the influence of typhoon and other meteorological factors, the precipitation concentration of the southern and central-eastern catchments in Zhejiang Province is higher than that of the central and Western catchments. This may explain why some catchments with lower average elevation and slope exhibit relatively high BFI values. In addition, due to the quality of data, the impact of soil and geological structure on baseflow remains to be revealed. The results of this study are helpful to understand the spatiotemporal distribution of baseflow in humid hilly areas, and can provide theoretical support for meeting ecological and social water needs in Zhejiang Province.