[A-OS10] Continental Oceanic Mutual Interaction - Planetary Scale Material Circulationn

[AOS10-P01] How the delay time the rainfall flow into the lake?

*Maho Iwaki¹, Yosuke Alexandre Yamashiki², Takashi Toda¹, Chunmeng Jiao³, Michio Kumagai⁴ (1.Lake Biwa Museum, 2.Kyoto University, 3.Lake Biwa Environmental Research Institute, 4.Ritsumeikan University)

Keywords:Frequency response function, Lake water levels, Lake Biwa

Our study indicated that an impulse response function can determine the precipitation retention time at the surface of a catchment area and estimate the time required for the precipitation to reach a lake. We calculated the response function of rainfall to water levels in Lake Biwa during summer and winter. The calculated delay time increased with increasing river length and river catchment area. Based on the time scales, we divided the delay time after rainfall into two groups: those occurring due to direct rainfall in the lake and seiches, and river inflow (surface and return flows). We concluded that the rapid (direct rainfall into the lake, surface and quick return flows) and short-term response [surface flow, quick return flow, and slow return flow (or subsurface flow)] runoff patterns could be distinguished by considering the time scale of the delay time determined from the response function.
The shape of the response function reflects the lake system itself, enabling a better understanding of lake systems and dominant processes, even in arid areas. Delay time acquired from the response function may be useful for estimating the contribution of rainfall (evaporation) to the increase (decrease) in lake water levels, and other factors. Our method assists the analysis of lake systems by defining both input and output flows. For example, for endorheic lakes, rainfall is the input and evaporation is the output; for exorheic lakes, rainfall is the input and discharge is the output; and for lakes in arid regions, discharge volume (or rainfall) is the input and lake surface area (or evaporation volume) is the output. Therefore, the proposed method could be applied to different types of lake systems, where the response function could assist in developing watershed management strategies in response to climate change.