Special Issue on Grand Challenges in Hydrology

There is no question that we have come a long way in hydrology, but we may just be in the beginning yet. This paradox can be justified on many grounds. For instance: (1) while hydrology as the “study of water” is as old as the human civilization, it is still in an early phase of being established as a science in its own right; (2) although we have always studied water with respect to its surroundings, our understanding of the actual interactions between hydrologic systems and other natural/physical systems (e.g., climate, environmental, biological, ecological) is still in a state of infancy; and (3) while water has always been an integral part of humans, we are only now starting to study the influence of humans on water and vice versa, especially under the framework of coupled human-water relations. The state of hydrology, especially its future, is further complicated by the uncertainties associated with (1) population growth and exploitation/alteration of water and other natural resources, especially in the developing and least-developed regions where such resources are already scarce; and (2) impacts of global climate change on our natural and social systems at global, regional, and local levels.

Under these circumstances, a fundamental requirement toward true progress in hydrology is to identify the most challenging problems (or “grand challenges”) and particularly focus our studies on such. The grand challenges are defined by the depth of their scientific meanings and/or the breadth of their societal implications. While there is no doubt that we have made and continue to make efforts in this direction, what is also clear is that such efforts have unfortunately been far and few between. There is, therefore, a need to properly address this deficiency, which provides the motivation for the current special issue on Grand Challenges in Hydrology.

This special issue compiles articles that address some of the grand challenges in hydrology that require urgent attention. The contributors come from over 30 universities and research institutions across 11 countries around the world. The articles cover a wide range of topics and associated challenges: parameter estimation in hydrologic models and data issues—focusing on information content (Beven and Smith), resampling method (Sikorska et al.), and predictions in ungauged basins (Seibert and McDonnell); catchment classification (Sivakumar et al.); climate change impact studies—freshwater resources (Kundzewicz and Gerten), sea-level rise (Chang et al.), and downscaling method (Jang and Kavvas); groundwater—modeling and management (Ojha et al.) and water quality (Ramadas et al.); hydrosystem-ecosystem interactions (Zalewski); dams and development (Tortajada); and hydrology education (Ruddell and Wagener). Each article roughly qualifies as a review on the topic discussed, offering a comprehensive account of the current status, unresolved issues, and important directions for the future.

We, the guest editors, clearly recognize that the list of grand challenges compiled in this special issue remains incomplete because there are indeed many other topics that deserve serious consideration. Examples of such topics are (1) hydrologic measurement techniques; (2) emerging techniques for analysis of hydrologic systems (e.g., hydroinformatics); (3) land-use change hydrology; (4) surface water–groundwater interactions; (5) global water scarcity issues and solutions; (6) coupled human–water relations; and (7) transboundary water management (including the role of hydropolitics). The selection of the topics and challenges for this special issue was influenced by the following, among others: identification of all the grand challenges was a challenge in itself; and time constraints, especially faced by potential contributors of some topics. Nevertheless, we believe that this special issue is a very useful contribution to the discussion of grand challenges in particular and to the advancement of hydrology broadly.

We thank Rao S. Govindaraju, the editor in chief of this journal, for his encouragement and support for this special issue. Our thanks also to the Journal of Hydrologic Engineering editorial office staff for their support throughout the review process and to the ASCE publication department staff during production. The authors of the contributions obviously deserve our special thanks for their support and participation in this endeavor, despite their numerous commitments and time constraints. The special issue has also benefited from the following reviewers (in alphabetical order): Faisal Anwar, Stacey Archfield, Hakan Basagaoglu, Keith Beven, Luca Chiari, Luis Chicharo, M. Dinesh Kumar, Ryan Dupont, Ryo Fujikura, Olivia Green, Naota Hanasaki, Denis Hughes, Sanjeev Kumar Jha, Vinayakam Jothiprakash, Ungtae Kim, Vincent Kotwicki, Laura Lautz, Salvatore Manfreda, Lucy Marshall, Alberto Montanari, Ioannis Nalbantis, Bethany Neilson, Jun Niu, Jayantha Obeysekera, Noriaki Ohara, Charles Perrin, Srivatsan Raghavan, Gerrit Schoups, Veena Srinivasan, and Jaeyoung Yoon. Their timely and constructive reviews have certainly enhanced the quality of contributions, and our sincere thanks to each and every one of them.