Estimating spatial patterns of wilting point deficit using a water balance model and a geographic information system

A geographic information system was used to integrate soil maps and soils data with a simple climatological water balance model to assess the spatial distribution of soil moisture deficit (accumulated wilting point deficits) over an area of approximately 250 000 hectares on the Canterbury Plains. Spatial patterns of soil moisture deficit were analysed for 30-year average conditions, dry and wet years, and selected regimes of atmospheric circulation (e.g., El Nino). After dry years, highest deficits occurred in years with predominantly westerly circulation and in La Nina years. El Nino and Easterly years had smaller deficits. The ability of the Geographic Information System to integrate data from sources with varying resolution to show spatial and temporal variations in patterns of soil moisture deficit illustrates the value of this technology in agroclimatic studies.