Advancements in Simulating Land Hydrologic Processes for Land Surface Modeling (LSM) Hua Su Presentation for Physical Climatology

Typical One Dimensional Soil Column in LSM Coupled with Multiple Land Surface Hydrologic Processes

Infiltration Surface Runoff Recharge Groundwater Runoff Water Table Level Soil Reservoir Groundwater Reservoir Five Components as Major Impediments for Simulating Surface Hydrology in LSM 1. Surface runoff; 2. Surface infiltration; 3.Soil reservoir recharge (or infiltration) to groundwater reservoir; 4.The location of water table, i.e., the location of surface interface of groundwater reservoir; 5. The runoff of groundwater reservoir, i.e., the groundwater discharge.

Why they are difficult? (a lot of reasons) Infiltration Surface Runoff Recharge Groundwater Runoff Water Table Level Soil Reservoir Groundwater Reservoir Complexity of land surface Highly heterogeneous, within a gird cell the soil, vegetation and topography can vary greatly Model limitation, we only have a few number of soil layers to portray the soil reservoirs and each layer’s thickness can not change during each LSM run; We do not have a explicit layer for describing groundwater reservoir; Spatial resolution put constraints on simulating groundwater runoff, generally we can not quantify the interaction between aquifer and river at riparian areas......

How to incorporate subgrid heterogeneity of soil properties into one dimensional soil column Example Subgrid soil potential infiltration capacity (ranking) How to calculate the total infiltration excess runoff given the homogeneous precipitation in the gird ?

Distribution of soil moisture capacity and potential infiltration rate, by Liang & Xie, 2003 Infiltration excess runoff Saturation excess runoff

Moving boundary: Water Table Level, how to predict the accurate location of water table in each LSM simulation step Lower boundary flux equation Water balance equation in soil reservoir and groundwater reservoir by Liang & Xie, 2003 Numerically solve, water table level based on finite element method

How to calculate groundwater recharge in LSM one-dimensional soil column Infiltration Surface Runoff Recharge Groundwater Runoff Water Table Level Soil Reservoir Groundwater Reservoir Calculate the recharge as function of soil moisture difference between two reservoirs, and the vertical distance between groundwater table and mid- point of the lowest layer by Chen & Hu, 2004

How to calculate groundwater discharge in LSM one-dimensional soil column, without explicitly representing the interaction between aquifer and river Predefine subgrid distribution of water table using Gamma distribution Derive the relationship between gird average water table and discharge by Yeh & Eltahir, 2005

Achieve encouraging results after these modification on baseline LSM by Yeh & Eltahir, 2005 by Liang & Xie, 2003

Limitation of these modification Parameters in statistical distribution function are sometimes difficult to derive (need large amount of soil hydraulic data or water table data) ; Numerical work might be too much, especially when used for global simulation; Some physically related hypothesis may not be appropriate, especially those on point scale; Explicit representation of subgrid heterogeneity; Moving boundary of water table; Processes based simulation of groundwater discharge Implication: Following items are especially important to updating current LSM