Magnitude-frequency analysis of water redistribution along a climate gradient in Spain

Banded patterns in soils and vegetation form part of important discontinuities on semi-arid slopes in Spain. At fine scales (<1 m) vegetation and well-structured soils are often located at the outer rim of small terracettes. Together they form banded patterns, distributed in a scattered way along contour lines. The objective of this study is to quantify the amount of surface water redistribution at fine spatial scales for three areas in Spain, having different rainfall regimes (290, 394 and 688 mm annual rainfall). Rainfall simulations experiments were carried out to determine runoff and infiltration characteristics of the bare and vegetated zones. The results of these experiments are combined with an analysis of the rainfall magnitude-frequency characteristics of the three area's. The combination of these two type of data has resulted in the calculations of a Redistribution Index (RI). The results showed a high variability in surface water redistribution from bare areas to banded vegetated zones. The combination of the infiltration characteristics at the different sites with the magnitude-frequency data of rainfall shows that most of the surface water redistribution originates from short storms with a duration of 10 min. The largest amount of redistribution during these events is found for areas having an intermediate rainfall regime with an annual rainfall of 394 mm. The Redistribution Index developed during this study provides a rapid methodology that can be used to evaluate differences in the importance of surface water redistribution in different banded vegetation structures at a regional scale. (C) 1999 Published by Elsevier Science B.V. All rights reserved.