Streamflow Recession and Dominant Factors in the Nanling Mountain Forest Catchment

Abstract

Little attention has been paid to dry season streamflow and groundwater recharge dynamics compared to the systematic focus on measuring total annual streamflow changes associated with forest. However, in the tropics and subtropics, especially in regions with uneven seasonal distribution of precipitation, dry season streamflow and groundwater recharge are of great importance for the riverine ecosystem stability and downstream water supply safety. Recession analysis of -dQ/dt~Q is widely used for determining the catchment storage-discharge relationship and predicting dry season streamflow processes. When dQ/dt~Q plots of streamflow recession are constructed for individual events, the slopes of the curves are near constant in log space, but the intercepts vary with time. Previous studies used event-based analysis to hypothesize that the shifts in intercept in dQ/dt~Q curves were due to variations in concurrent evapotranspiration (ET), which is consistent with the dominant belief regarding controls on streamflow recession. On the contrary, increasing evidence suggests the possibility that other factors such as soil moisture, groundwater recharge, or active drainage network may play a role in dQ/dt variations. However, no consensus has been reached on the determinants of the shift. By using an event-based recession analysis, an experimental catchment with long-term hydrometeorological observations was selected to investigate the streamflow recession in the Nanling mountain forest. Our results showed that 1) faster recession rates were more likely to occur under dry conditions than those under wet conditions; 2) groundwater depth varied consistently with soil moisture in response to precipitation, indicating high soil infiltrability; 3) a significant correlation between the intercept a and concurrent groundwater depth demonstrated its potential role as explanatory variable of streamflow recession; 4) as a losing stream (groundwater depth always larger than 5.0 m near the catchment outlet), water loss to groundwater recharge appears to be the dominant factor affecting streamflow recession.

Keywords

• nanling mountain
• storage-discharge relationship
• low flow
• soil moisture
• groundwater recharge
• evapotranspiration