GISHydro97 - Soilwater

Soil Water Balance Module

Center for Research in Water Resources, University of Texas at Austin


Soil water balancing refers to the partitioning of precipitation into evaporation, and runoff or recharge by using a water balance calculation applied to a volume of soil.

This module provides exercises to demonstrate how simple soil-water budget calculations can be made in ArcView. Exercises for two sample study areas are available to demonstrate the procedures, one in Morocco and one in Texas. The input data for these exercises are taken from global data sets and therefore similar exercises can be run at any location in the world. The Texas water balance calculations were done at a later time than those for Morocco, so a somewhat more sophisticated approach for estimating evapotranspiration and storm runoff is described. In the Morocco exercise, an example of computing potential evapotranspiration using the Priestley-Taylor method is demonstrated while the Texas exercise uses a Bowen ratio approach for estimating evapotranspiration directly from the modeled soil moisture estimate.

The Morocco exercise is done strictly using Avenue scripts while the Texas exercise explains how to make the calculations using just Avenue or using a combination of Avenue and FORTRAN. The procedure combining Avenue with FORTRAN (described in the last part of the Texas exercise) is much faster computationally. This is partly due to the fact that the FORTRAN routine is written more efficiently, but also due to the fact that Avenue is an interpreted language and FORTRAN is compiled. Soil water balance calculations for the entire state of Texas took about 30 minutes using the Avenue routine and only 5 seconds using the FORTRAN routine. It took about 1 minute for an Avenue script to write the FORTRAN input file. Times reported are for a machine with a 133 MHz processor.

Sample Exercises and Data are Available on this CD


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These materials may be used for study, research, and education, but please credit the authors and the Center for Research in Water Resources, The University of Texas at Austin. All commercial rights reserved. Copyright 1997 Center for Research in Water Resources.