Two distributed parameter models, a one-dimensional (1D) model and a two-dimensional (2D) model, are developed to simulate overland flow in two small semiarid shrubland watersheds in the Jornada basin, southern New Mexico. The models are event-based and represent each watershed by an array of 1-m2 cells, in which the cell size is approximately equal to the average area of the shrubs. Each model uses only six parameters, for which values are obtained from field surveys and rainfall simulation experiments. In the 1D model, flow volumes through a fixed network are computed by a simple finite-difference solution to the 1D kinematic wave equation. In the 2D model, flow directions and volumes are computed by a second-order predictorâ€“corrector finite-difference solution to the 2D kinematic wave equation, in which flow routing is implicit and may vary in response to flow conditions. The models are compared in terms of the runoff hydrograph and the spatial distribution of runoff. The simulation results suggest that both the 1D and the 2D models have much to offer as tools for the large-scale study of overland flow. Because it is based on a fixed flow network, the 1D model is better suited to the study of runoff due to individual rainfall events, whereas the 2D model may, with further development, be used to study both runoff and erosion during multiple rainfall events in which the dynamic nature of the terrain becomes an important consideration. Copyright Ã£ 2006 John Wiley & Sons, Ltd.

VL - 20 UR - files/bibliography/JRN00452.pdf AN - JRN00452 N1 - //NMSU//LTER IV//Entered 06/09/2006 ER - TY - JOUR T1 - Modeling runoff and runon in a desert shrubland ecosystem, Jornada Basin, New Mexico JF - Geomorphology Y1 - 2003 A1 - David A. Howes A1 - Athol D. Abrahams KW - article KW - articles KW - hydrology, grassland KW - hydrology, rainfall simulation KW - hydrology, runon KW - hydrology, shrubland KW - hydrology, surface runoff KW - journal KW - journals KW - model, runoff KW - model, runon KW - runoff, model KW - water flow, model AB -A new two-dimensional (2D) distributed parameter model is developed to simulate overland flow in two small semiarid shrubland watersheds in the Jornada Basin, southern New Mexico. The model is event-based and operates at the scale of the individual shrub, each watershed being represented as a set of 1-m^{2} cells. In the model flow directions and volumes are computed by a second-order predictor-corrector finite difference scheme (Davis, 1988), which is employed to solve the two-dimensional kinematic wave equation. Thus, flow routing is computed implicitly and may vary in response to flow conditions. The model uses only six parameters for which values are obtained from field surveys and rainfall simulation experiments. The model underpredicts runoff from the watersheds due to the measured values of saturated hydraulic conductivity K_{s} for intershrub areas being too high. This is because the runoff plot experiments used to estimate K_{s} were conducted at the beginning of summer on surfaces with degraded seals, whereas most summer storms occur on surfaces that have experienced recent rainfall and have better developed seals. Model performance is much improved when K_{s} is treated as a calibration parameter. The importance of runon infiltration in supplying water to shrubs is investigated for a range of rainfall and antecedent soil moisture conditions using the 2D model. On average, runon infiltration accounts for between 3 and 20% of the total infiltration in the soil under a shrub. The most favorable conditions for runon infiltration are an initially wet soil and a low mean rainfall rate.