1 Climate Change and Groundwater is a compendium of thirteen papers by various authors selected from the special session on ‘Impact of Climate on Groundwater Resources’ organized by the International Association of Hydrologists working group during the XXXII International Geological Congress held in August, 2004 in Florence, Italy. These papers describe the groundwater situation in different areas of the world, climate change being the common link. Several papers consist of simplified versions of previously published scientific papers, and are therefore easy to read and accessible to diverse readers.

2 As underlined in the article by Seiler et al., few issues have raised as much scientific and political attention and controversial debate as the effect and consequences of greenhouse gases on global warming. Warming will continue to create environmental problems, among the most severe of which will likely be related to water resources. Although climate scientists agree that surface temperatures have increased, the extent and spatial distribution of modifications in precipitation and other components of the hydrological cycle over the globe are much less well understood (Rivard et al. 2009). As noted by Jyrkama and Sykes (2007), the relationship between climate and groundwater is indirect and complex, and thus, difficult to quantify. Moreover, the intrinsic difficulty of estimating recharge and human activities (e.g. changes in land uses and in water exploitation) make the assessment even more complex, which is probably why much more attention has so far been focused on the effect of climate change on surface water. This book is, therefore, a very welcome initiative.

3 Groundwater constitutes the largest freshwater resource on earth, mainly because aquifers have a large storage capacity and offer protection from evapotranspiration, which represents a large component of the water cycle in arid countries. Therefore, groundwater is often viewed as having a key role in the future, either to alleviate severe drought situations (Dragoni and Sukhija) or to solve problems of water supply (Sinha and Navada). Some of the papers in this volume provide suggestions for alternatives to conventional water supplies, such as exploitation of deep aquifers containing fossil water (or for which the recharge rate is smaller than 10 mm/y), artificial recharge, and recycling procedures. In cases where deep aquifers were studied (e.g. Seiler et al.; Sinha and Navada; Sukhija), evidence indicates that they are unaffected by climate change and that they may be resilient to such changes over millions of years. The role of geology (i.e. aquifer types) may therefore, in some cases, overweigh the climate effect (Benderev et al.), demonstrating that groundwater can indeed be a strategic resource even in extreme or highly variable climatic conditions.

4 The volume contains three general papers. The introductory paper by the editors (Dragoni and Sukhija) provides a good overview of approaches that have been employed to study the effect of climate change on groundwater. The second paper (Seiler et al.) discusses the transient response of groundwater systems to climate change and its implications for water resource management. The last general paper (Salgot and Torrens) focuses on the use of reclaimed water, given that climate change will aggravate water scarcity in many regions and therefore increase the need for alternatives to conventional pumping of water.

5 The remaining ten papers present case studies on a variety of subjects, focusing on 1) historical data to study the evolution of spring discharge and identify drought periods (Benderev et al.; Ducci and Tranfaglia; Rapti-Caputo and Helly), and to evaluate statistical trends (Polemio and Casarano); 2) quantifying recharge in the future using numerical modeling (Scibek et al.); 3) spectral analysis to study the effect of oceanic – atmospheric patterns on groundwater levels in order to detect the presence of short and long-term cycles (Luque-Espinar et al.); 4) isotopic analyses applied to paleoclimate studies of groundwater in deep aquifers that were recharged during humid episodes 3000 – 9000 years BP (Geyh and Ploethner; Sinha and Navada; Issar); and 5) exploitation of deep aquifers and use of artificial ponds to adapt to an expected increase in droughts (Sukhija).

6 This series of papers clearly highlights the major difference in concerns between regions with high and low precipitation. In humid areas, people worry about future climate changes, whereas in arid countries, concerns mainly focus on actual (deficient) supply, and scientists mainly study past climate change (up to several thousands of years ago) in an attempt to find freshwater or to explain the presence of fossil water and variations in spring discharge rates. In fact, only the Canadian paper (Scibek et al.) uses synthetic climate forecasts from global climate models to study and quantify the impacts of future climate change on aquifer recharge. Most of the papers are devoted to studies conducted in arid to semi-arid countries, where water stress is already present, such as Greece, southern Italy, India, Pakistan (Thar Desert), Israel, and the West Bank.

7 The book covers a broad range of topics presented as case studies that examine varied climatic, geological, and hydrogeological conditions, from the history of deep aquifers containing fossil water, to ancient water supplies and their strong link with the development of civilizations, to past, actual and future recharge and discharge rates. Numerous graphs, tables, maps, and figures (although in black and white) have been included to provide visual support to the reader.

8 However, the book contains some minor flaws. First, the title of the book may be misleading for people from countries with high or moderate precipitation, as one may be led to believe that the book focuses on the quantification of future aquifer recharge and potential. It is regrettable that there are no papers focusing on Oceania or Africa, two areas where climate change has had well-documented, dramatic effects. In addition, it is somewhat disappointing that none of the papers discusses the use of an integrated (coupled) surface water – groundwater approach, particularly in view of current and forthcoming water cycle changes. The inclusion of a world map indicating the location of each study would have been an asset to the publication.

9 The paper by Benderev et al. has some problems regarding language use. More rigorous editing could have helped prevent misconceptions arising from awkward word usage, but this does not negatively affect comprehension of the paper. Only one paper (Scibek et al.) appeared poorly suited to the purpose of the book. The paper is very long and the level of scientific detail is close to that of the original research from which it was taken, in contrast to the other papers. In the authors’ defense, this is the only paper that dealt simultaneously with climate models, downscaling, weather generators, and infiltration and groundwater flow models, although the uncertainties in the use of these synthetic data are high.

10 What emerges from the book is that recharge is critically decreasing or is low in many areas, and that over-exploitation of groundwater resources has led to the deterioration of ground-water quality and quantity. However, regardless of whether these observed changes are part of long-term warming cycles or not, water resource availability has become problematic in many parts of the world, especially in arid and semi-arid regions. Research to predict changes and to find potential sources and adaptations, as outlined in this volume, is therefore crucial.

11 Overall, the book has a good balance of statistical and deterministic studies, scientific data, presentation of current groundwater conditions, and potential solutions to decreasing supplies. It focuses on climate change without a protracted discussion of global warming causes, but with innovative analyses of the consequences of groundwater withdrawals and changing climates over geological time-scales. Finally, Dragoni and Sukhija underline an important issue in their paper: the need for a high quality network of data collection, including groundwater-related data such as water levels and withdrawal or discharge rates. This has also been mentioned in other publications, but it is well worth restating.