Soil Water‐Holding Capacity Assessment in Terms of the Average Annual Water Balance in Southern Spain

Abstract

Knowledge of the soil water‐holding capacity, w0, is essential to the evaluation of regional soil water balance. In this paper, we produced a map of w0 for the region of Andalusia, southern Spain, using pedotransfer functions (PTFs) and geostatistics. The information available consisted of analytical and morphological data from 521 soil profiles in the region, and the 1:400 000 soil map of Andalusia. The w0 values were calculated using 10 published PTFs. The soil map only slightly improved the spatial interpolation of the PTF‐calculated w0's. The PTF estimates for w0 ranged from near 0 to 235 mm, with an average value of 110 mm and a SD of 48 mm. Since no independent field observations were available, the w0 estimates were evaluated in terms of the average annual total runoff and actual evapotranspiration. Both components were calculated at 160 meteorological observatories using a simple bucket water balance model, driven by daily meteorological data. The spatial variability of w0 had little effect on the calculated average annual water balance of the region. Increasing w0 to 150 to 200 mm produced a better fit of the water balance predicted with Budyko's empirical functions. The difference could be partly explained by seasonality‐related characteristics of the climate in the region. Comparison of the results with other studies suggests that the estimated w0 values should be increased by 45%. These differences can be attributed entirely to an inconsistent definition of field capacity (FC).