Lili Yao

and 4 more

Climate variability, in terms of the climatic fluctuations in precipitation and potential evapotranspiration, impacts the variability of runoff at different timescales. This paper developed a new daily water balance model which unifies the probability distributed model and the SCS curve number method, and provides a unified framework for water balances across different timescales. The model uses a daily step but can be forced with climate inputs varying at different timescales. The model is applied to 82 MOPEX catchments, and the runoff at a coarser timescale is aggregated from the daily runoff. For runoff at each timescale, the relative role of each climate variability (daily, monthly, or inter-annual variability) is evaluated by comparing the modeled runoff forced with the climate variability at two consecutive timescales. It is found that the runoff variability at the daily, monthly, and annual scale is primarily controlled by the climate variability at the same timescale. The monthly climate variability significantly contributes to both the daily and inter-annual runoff variability. However, both daily and inter-annual climate variability play much smaller roles in monthly runoff variability. Besides monthly climate variability, mean annual runoff receives considerable contribution from the inter-annual climatic variability, which is often disregarded in previous studies. The quantitative evaluation of the roles of climate variability reveals how climate controls runoff across different timescales.

Lili Yao

and 1 more

The control of land surface topography on the configuration of groundwater table has been recognized and well explored. However, the control of bedrock topography on water table is much less studied, potentially due to the limited observations of bedrock. This paper evaluates the controls of both surface and subsurface topography on the spatial distributions of steady-state water table and the corresponding water storage at the catchment scale based on numerical simulations. Numerical models with different topographic features are developed using MODFLOW (USG). When water table is shallow, the control on the spatial distributions of water table is dominated by land surface topography (i.e., water table is approximately parallel to land surface); with the increase of water table depth, the role of land surface topography decreases; when water table is deep and close to bedrock surface, the spatial distributions of water table is dominated by bedrock topography (i.e., water table is approximately parallel to bedrock surface). For land surface-dominated water table, storage capacity in unsaturated area is spatially uniform, which is the underlying assumption of TOPMODEL; however, for bedrock-dominated water table, water storage in unsaturated area is spatially uniform, which is the underlying assumption of VIC-type model. The systematical variations of the controls of surface and subsurface topography on water table configuration provide a framework to unify saturation excess runoff models by treating TOPMODEL and VIC-type model as two endmembers.