Hydraulic conductivity of the soil matrix dynamically responds to chan
ges in the surrounding environment. Therefore, infiltration parameters
for the Green-Ampt equation should change for each storm event in con
tinuous simulation models. This study focused on improving Water Erosi
on Prediction Project (WEPP) model estimates of runoff using over 220
plot-years of natural runoff plot data from 11 locations. By optimizin
g the effective Green-Ampt hydraulic conductivity, K-e, for each event
within the simulation, a method of correlating hydraulic conductivity
on any given day to many other parameters was established. Factors wi
th significant correlation to optimized values of K-e fell into three
distinct categories; (1) factors related to soil crusting and tillage;
(2) factors related to event size; (3) factors related to antecedent
moisture conditions. Equations were developed to represent the tempora
l variability of hydraulic conductivity for each group. The equation d
escribing the decrease in hydraulic conductivity owing to crusting use
d an exponential decay function based primarily on cumulative rainfall
kinetic energy since last tillage, a soil stability factor, and a cru
st factor. The relationship between hydraulic conductivity and event s
ize was characterized using an exponential relationship with total rai
nfall kinetic energy. The final adjustment used the moisture content i
mmediately below the infiltration zone to account for the influence of
antecedent moisture conditions on optimized hydraulic conductivities.
All three adjustments were incrementally incorporated into WEPP and e
ach improved the average model efficiency.