Simulation of soil moisture and other components of the hydrological cycle using a water budget approach

Accurate simulation of soil moisture content at any time of the year is important to agriculture in dry regions due to the vital role soil moisture plays in crop production. In certain applications, such as drought monitoring, other components of the hydrologic cycle such as runoff, snowmelt runoff, deep drainage and evaporative loss must also be accurately estimated. The goal of this study was to develop a model which accurately accounts for the major components of the hydrological cycle in order to simulate soil moisture content for drought monitoring and crop yield prediction. The versatile soil moisture budget (VSMB) was evaluated and modified to improve the prediction of soil moisture content, runoff from rainfall and snowmelt, drainage of moisture out of the root zone and soil surface temperature. The modified components of the model were independently tested and validated using field and published data. The soil moisture output from our modified model correlated well with observed changes in soil moisture during the growing season under wheat, fallow and over the winter. The moisture content of the surface layer was simulated with greater accuracy than that of deeper layers. The soil moisture simulated by the modified model compares better with measured values than that simulated using the original version of the VSMB. The simulation of snow dynamics at Lethbridge, a chinook-dominated region, gave credibility to the snowmelt runoff predicted by the model.