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Spatial average aquifer recharge through atmospheric chloride mass balance and its uncertainty in continental Spain
Author(s) -
Alcalá Francisco J.,
Custodio Emilio
Publication year - 2012
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.9556
Subject(s) - groundwater recharge , aquifer , environmental science , spatial variability , hydrology (agriculture) , soil science , geology , groundwater , statistics , mathematics , geotechnical engineering
Abstract The atmospheric chloride mass balance (CMB) method allows spatial evaluations of the average diffuse aquifer recharge by rainfall ( R ¯ ) in large and varied territories when long‐term steady conditions can be assumed. Often, the distributed average CMB variables necessary to calculate R ¯ have to be estimated from the available variable‐length data series, which may be of suboptimal quality and spatial coverage. This paper explains the use of these data and the reliability of the results in continental Spain, chosen as a large and varied territory. The CMB variables have been regionalized by ordinary kriging at the same 4976 nodes of a 10 km × 10 km grid. Nodal R ¯ values vary from 14 to 810 mm year –1 , 90% ranging from 30 to 300 mm year –1 . The recharge‐to‐precipitation ratios vary from 0.03 in low‐permeability formations and semiarid areas to 0.65 in some carbonate massifs. Integrated average results for the whole of continental Spain yield a potential aquifer recharge of 64 km 3 year −1 , the net recharge over permeable formations (40% of the territory) being 32 km 3 year −1 . Two main sources of uncertainty affecting R ¯ (given by the coefficient of variation, CV ), induced by the inherent natural variability of the variables ( CV R ) and from mapping ( C V R K ), have been segregated. The average CV R is 0.13 and could be improved with longer data series. The average C V R Kis 0.07 and may be decreased with better data coverage. The R ¯ estimates were compared with other regional and local recharge estimates, R ¯ being 4% and 1% higher, respectively. Copyright © 2012 John Wiley & Sons, Ltd.