Computers & Geosciences 31 (2005) 15–27 A GIS tool for hydrogeological water balance evaluation on regional scale in semi-arid environments $ I. Portoghese , V. Uricchio, M. Vurro Istituto di Ricerca Sulle Acque del CNR, Sezione territoriale di Bari, Via F. De Blaso, 5 70123 Bari, Italy Received 17 December 2002; received in revised form 1 April 2004 Abstract A GIS tool to evaluate hydrogeological water balance based on a mass-balance model applied to surface and subsurface systems is discussed. The tool is designed for managers responsible for groundwater resource planning during conditions of water shortage. In developing the tool, the natural groundwater recharge was evaluated th the application of a soil water balance equation, and defined as the difference between the inflows (rainfall, irri and the outflows (plant evapotranspiration, surface run-off). A distributed approach was used in the soil water b equation to account for the spatial variability of climate and landscape features. Conversely the groundwater b was calculated on a watershed or aquifer scale, usinga lumped water balance equation, in which withdrawals for differentuses were estimated together with inflows from other water bodies and coastal outflows.The modelwas implemented on a GIS platform with an automatic routine that manages all the data sets required and allows fo forecasting of groundwater storage volumes. Furthermore, the model was able to evaluate agricultural water d under different climatic and management scenarios. A tool which provides a summary of the results and performs a statistical analysis for any portion of the study area was also implemented. The model was applied to a coastal Southern Italy. The averaged groundwater balance calculated by the model was in agreement with the piezom and chlorine concentration trends measured in selected monitoringwells. r 2004 Elsevier Ltd. All rights reserved. Keywords: Groundwater balance; Surface water balance; GIS; Water resources management; Hydrology 1. Introduction The European Union, in its water framework directive (WFD) states new principles and guidelines in water resources policies. This document points to ‘‘the need to establish procedures for the regulation of abstraction offreshwaterand for the monitoringof freshwaterqualityand quantity’’(European Union, 2000).The WFD established a framework for the protection ofgroundwater, which promotes ‘‘sustain- able water use based on a long-term protection of available water resources’’. Furthermore, member States are required to ‘‘ensure a balance between abstraction and recharge of groundwater’’, with the aim of achieving good groundwater quality and quantity within at most 15 years.Moreover,accordingto the Committee on Hydrologic Science (1999), research on climate-hydrol- ogy linkages should be broadened to address issues of groundwaterrecharge,evaporation,andbasin-scale water balance. ARTICLE IN PRESS www.elsevier.com/locate/cageo 0098-3004/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cageo.2004.09.001 $ Code on server at http://www.iamg.org/C6Editor/index.htm Correspondingauthor. Tel.: +39 080 582 0540; fax: +39 080 531 3365. E-mail address: irsaip43@area.ba.cnr.it (I. Portoghese).