River discharge recovery lag in the small and medium-sized rivers occurred in response to climate change and human activities

To cope with the negative impacts of climate change and human activities on water resources in basins, positive measures such as interbasin water transfer projects and efficient water resource policies have been implemented worldwide, and these measures have had an obvious effect on the discharges of large rivers. However, for small and medium-sized rivers, the impact is still unclear due to a deficiency in river discharge data. To answer this question, the Haihe River Basin (HRB), located in the core area of economic development in North China, was selected as a typical research area. Remote sensing hydrological station technology, which combines unmanned aerial vehicles (UAVs), satellite remote sensing, and in situ surveying, was applied to obtain the monthly scale discharges of 16 small and medium-sized river sections in the last 20 years (2000-2020). In addition, an accuracy evaluation and spatiotemporal change analysis of the discharge results, which were influenced by interbasin water transfer projects and efficient water resource management policies, were also carried out. The results show that 1) 10 of the 16 river sections in the basin had a downward trend in the past 20 years, with an average annual decrease of 2.13%, and these sections were located in the plain areas; the remaining 6 sections located in the mountain areas had an upward trend, with an average annual increase of 1.72%; 2) we found that the river discharges of small and medium-sized rivers recovered with a lag that reached 3-11 years for the 16 rivers, and this lag for the mountain rivers was 3-9 years and for the plain rivers, it was 8-11 years; and 3) the main cause of this lag was the heavy exploitation of groundwater in the basin, which led to increased water volume from interbasin water transfers mainly to supplement groundwater resources, while surface water resources could not be quickly and sufficiently supplemented to restore them to the original natural discharge. Our research not only unmasks the changes of small and medium-sized river discharge in areas strongly affected by human activities but also helps people to better understand the response of small and medium-sized river discharges to the complex environmental changes incurred by climate change and serious human activities.

Automated summary

In order to address the negative impacts of climate change and human activities on water resources in basins, positive measures such as interbasin water transfer projects and efficient water resource policies have been implemented worldwide, resulting in noticeable effects on the discharges of large rivers. However, the impact on small and medium-sized rivers remains unclear due to insufficient river discharge data. This study focused on the Haihe River Basin in North China and utilized remote sensing hydrological station technology to obtain monthly scale discharge data for 16 small and medium-sized river sections in the past 20 years. The results showed both downward and upward trends in river discharges, with lags in recovery attributed to heavy groundwater exploitation in the basin.