Climate and the Hydrological Cycle

Transcription

1 Climate and the Hydrological Cycle Edited by Marc Bierkens Utrecht University, The Netherlands Han Dolman Vrije Universiteit Amsterdam, The Netherlands Peter Troch University of Arizona, USA An in-depth overview of the role of the hydrological cycle within the climate system, including climate change impacts on hydrological reserves and fluxes, and the controls of terrestrial hydrology on regional and global climatology. This book, composed of self-contained chapters by specialists in hydrology and climate science, is intended to serve as a text for graduate and postgraduate courses in climate hydrology and hydroclimatology. It will also be of interest to scientists and engineers/practioners interested in the water cycle, weather prediction and climate change. 1. The Role of the Hydrological Cycle in the Climate System 2. Evaporation 3. Physics of Evaporation and Atmospheric Boundary Layers Over Land 4. Precipitation Physics and Rainfall Observation 5. Land Surface Hydrology 6. Land Surface Schemes and Climate Models 7. Arctic and Snow Hydrology 8. Dynamics of Glaciers, Ice Sheets and Global Sea Level 9. Feedback Mechanisms: Precipitation and Soil Moisture 10. Feedback Mechanisms: Land Use, Hydrology and Carbon 11. Palaeohydrology: An Introduction 12. Groundwater Palaeohydrology 13. Global Warming and the Acceleration of the Hydrological Cycle 14. Climate Change and Hydrological Impact Studies 15. Remote Sensing for Hydrological Studies Sponsored by: IAHS Special Publication 8 (October 2008) ISBN (Paperback); xvi pages Price Please send book orders and enquiries to: Mrs Jill Gash jilly@iahs.demon.co.uk IAHS Press, Centre for Ecology and Hydrology tel.: Wallingford, Oxfordshire OX10 8BB, UK fax: / Book prices include postage worldwide. IAHS Members receive discounts on IAHS publications. See for information about IAHS (the International Association of Hydrological Sciences), membership, publications, meetings and other activities.

2 1 The Role of the Hydrological Cycle in the Climate System by Han Dolman 2 Evaporation by Eddy Moors 3 Physics of Evaporation and Atmospheric Boundary Layers Over Land by Albert A. M. Holtslag & Michael B. Ek 4 Precipitation Physics and Rainfall Observation by Remko Uijlenhoet 5 Land Surface Hydrology by Peter A. Troch 6 Land Surface Schemes and Climate Models by Bart Van den Hurk 7 Arctic and Snow Hydrology by Rutger Dankers 8 Dynamics of Glaciers, Ice Sheets and Global Sea Level by Roderik Van de Wal 9 Feedback Mechanisms: Precipitation and Soil Moisture by Marc Bierkens & Bart van den Hurk 10 Feedback Mechanisms: Land Use, Hydrology and Carbon by Han Dolman 11 Palaeohydrology: An Introduction by Patrick W. Bogaart 12 Groundwater Palaeohydrology by Henk Kooi 13 Global Warming and the Acceleration of the Hydrological Cycle by Peter A. Troch 14 Climate Change and Hydrological Impact Studies by Hans Middelkoop 15 Remote Sensing for Hydrological Studies by Steven de Jong, Hans van der Kwast, Elisabeth Addink & Bob Su

3 Foreword Water vapour is the most important of all the greenhouse gases. Were there no water vapour in the troposphere, near-surface air temperatures would be several tens of degrees less. Greenhouse warming research investigates a potential change of several degrees in this already existing substantial warming, and explores the impact of such a change. Consequently, understanding and correctly modelling how more water vapour in the atmosphere will amplify the contribution to near-surface warming caused by other greenhouse gases, and how this extra water may alter cloud cover and therefore surface solar radiation, are arguably the two biggest challenges for improved climate change prediction. At the same time, it is through potential changes in the nature and availability of precipitation falling over land surfaces, and ensuing changes in the water available for crops, river flow, and groundwater recharge, together with possible associated changes in evaporative demand, that a changing climate will have its most direct impact on human welfare and ecological services. This is all the more true because these climate-related changes in the Earth s hydrological cycle, which are the indirect result of the growth in human population and human expectations, will exacerbate the inevitable stress on water resource systems that will result from the direct impact of a massively growing global population on water demand and water quality. Consequently, the importance of the relationship between climate and hydrology cannot be overstated. This book is motivated by the need to stimulate and foster this branch of science to address the challenge. The subject area it documents lies at the interface between climate science and hydrological science, and is identified in the preface as climate hydrology. The scope of this important emerging topic is massive, and consequently the scope of this book is also massive. In fact, the 15 chapters it contains cover much that is currently known in the fields of surface hydrology, hydrometeorology, and cold climate and remote sensing science, as well as exploring the interfaces and coupling processes that link these fields. Yet every one of the selfcontained chapters is written by an expert, and all are written with evident depth of perception and relevant understanding. Their collection together in this volume represents a huge new resource: a graduate level textbook and source of reference in the critical area of climate hydrology that was hitherto unavailable. This is a book which is timely, comprehensive, thorough and comprehensible, but above all, a book that is needed. Jim Shuttleworth February 2008 James W. Shuttleworth, Professor of Hydrology and Atmospheric Science University of Arizona, USA

4 Preface Traditionally, the terrestrial part of the hydrological cycle is studied by hydrologists while the atmospheric part is left to atmospheric scientists. Consequently, and unfortunately, these two branches of Earth Science have shown limited interaction, apart perhaps from the study of evaporation and precipitation generation. The last two decades have shown an increased interest in climate change and its impacts, not only by the atmospheric science community, but also by hydrologists. The first studies on hydrology and climate that were performed by hydrologists focused on the impact of climate change and variability on the water balance and river discharge. Recently, atmospheric scientists have turned more and more to hydrology to come up with better land atmosphere parameterizations in order to improve climate models and weather prediction. These developments have led to an almost separate hydrological discipline, called climate hydrology, in which hydrological systems are viewed as part of the climate system, being both influenced by climate change and variability, as well as constraining the climate system through positive and negative feedbacks. The study of the hydrological cycle in the context of the climate system has developed sufficiently to warrant a self-contained book on the subject. The purpose of this book is to provide an in depth overview of the role of the hydrological cycle within the climate system, including climate change impacts on hydrological stores and fluxes, as well as controls of terrestrial hydrology on regional and global climatology. The book is intended to serve as material for graduate and postgraduate courses in climate hydrology and hydroclimatology. Furthermore, its contents will be of interest to scientists and engineers/practitioners interested in the water cycle, weather prediction, and climate change. The book started out as lecture notes provided by the lecturers of an international summer course named Climate and the Hydrological Cycle which was held at Utrecht University, 4 15 July 2005, with 55 participants from various parts of the world. This was the first summer course organized by the Boussinesq Centre for Hydrology, which is the Dutch centre that aims to promote fundamental hydrological research. Its members are the university-based hydrology groups in The Netherlands, and we happily refer to the website ( for an overview of their activities. The lecture notes were reviewed by the editors, resulting in 15 self-contained chapters by specialists in the field of hydrology and climate science. The logic of the chapters contents follows that of the original course and is as follows: We start out with an introductory chapter providing an overview of the role of the hydrological cycle in the climate system. Next, we focus on the drivers of the hydrological cycle: evaporation and precipitation. Evaporation theory and observations are treated in Chapter 2, while Chapter 3 treats evaporation as part of the dynamics of the planetary boundary layer. Next, Chapter 4 provides a description of precipitation physics and of the various ways of observing precipitation, including remote sensing. In the following four chapters we focus on hydrological processes at the land surface

5 (Chapter 5) and how these processes are generally conceptualized in the land surface component of weather prediction and climate models (Chapter 6). As climate change is expected to have the greatest impact at the higher latitudes, Chapter 7 deals with hydrological processes of sub-arctic regions and how climate change impacts these processes. Chapter 8 is another cold chapter, describing the dynamics of glaciers and ice sheets and how these relate to sea level change. Because of their long turnover times, we sometimes forget that glaciers and ice sheets are also part of the terrestrial hydrological cycle. We are proud that we charmed a leading glaciologist to fill this gap. As the first part of the book (chapters 2 to 8) deals with the various components of the hydrological cycle, in the second part (chapters 9 to 14) the hydrological cycle is treated in its various modes of interaction with the climate system. We begin with two important feedbacks that are currently the subject of much research. First, the role of soil moisture precipitation feedbacks is treated in Chapter 9. These feedbacks are important at the sub-daily to seasonal time scale, i.e. the scale of weather prediction. In Chapter 10 we treat the exchange of carbon between land and atmosphere, which is intimately linked to hydrology. Understanding this feedback, which operates at larger time scales, is essential to predicting climate change. To understand how climate impacts hydrology, much can be learned from the past, while relics from the past may teach us a lot about past climate variability. This is the topic of Chapter 11, where an overview is given of methods to reconstruct the components of the terrestrial water balance in the past. The appendix to this chapter provides a review about the use of palaeo-climatological model experiments in understanding the sudden climate change at the end of the African humid period 6000 years ago. This case study exemplifies the importance of vegetation dynamics and hydrology in climate change. This chapter is followed with a review on groundwater palaeohydrology (Chapter 12), showing, through various types of tracers, that groundwater bodies are valuable repositories of past climate change information. The treatment of interaction between the hydrological cycle and the climate system culminates in two chapters about climate change. Chapter 13 deals with the much debated question as to whether climate change is already causing the hydrological cycle to speed up. Here the various, often contradictory, observational evidence is reviewed. Chapter 14 describes methods of determining the hydrological impact of climate change, including various ways of downscaling and bias-correcting climate scenarios. Much of the current research into the global water and energy cycle depends heavily on remotely sensing. Therefore, we complete the book with an overview of various remote sensing techniques and satellite missions designed to monitor components of the hydrological cycle (except for rainfall by radar, which is treated in Chapter 2). We would like to end this Preface by expressing our thanks. First, to the Dutch government funded research programme Climate Changes Spatial Planning, for financial support. Thanks to Nynke Vellinga for editing assistance and to Ton Markus and Margot Stoete of GeoMedio for fixing many of the figures. Finally, special thanks to Cate Gardner of IAHS Press for excellent guidance in preparing the book. Marc F. P. Bierkens Peter A. Troch A. J. (Han) Dolman Utrecht, February 2008

6 Contributors Elizabeth A. Addink Department of Physical Geography, Faculty of Geosciences, Utrecht University, The Netherlands Marc F. P. Bierkens Department of Physical Geography, Faculty of Geosciences, Utrecht University, The Netherlands Patrick Bogaart Hydrology and Quantitative Water Management Group, Center for Water and Climate, Department of Environmental Science, Wageningen University, The Netherlands Rutger Dankers Institute for Environment and Sustainability, Joint Research Centre, European Commission, Ispra (VA), Italy Steven J. de Jong Department of Physical Geography, Faculty of Geosciences, Utrecht University, The Netherlands A. H. (Han) Dolman Department of Hydrology and Geo-environmental Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, The Netherlands Michael B. Ek National Center for Environmental Prediction, Environmental Modelling Center, Suitland, Maryland, USA Albert A. M. Holtslag Meteorology and Air Quality Group, Center for Water and Climate, Department of Environmental Science, Wageningen University, The Netherlands Henk Kooi Department of Hydrology and Geo-environmental Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, The Netherlands Hans Middelkoop Department of Physical Geography, Faculty of Geosciences, Utrecht University, The Netherlands Eddy J. Moors Earth System Science and Climate Change Group, Department of Environmental Science, Wageningen University and Research Centre, The Netherlands Z. (Bob) Su Department of Water Resources, International Institute for Geo-Information Science and Earth Observation (ITC), Enschede, The Netherlands Peter A. Troch Surface Water Hydrology Group, Department of Hydrology and Water Resources, University of Arizona, Tucson, Arizona, USA Remko Uijlenhoet Hydrology and Quantitative Water Management Group, Center for Water and Climate, Department of Environmental Science, Wageningen University, The Netherlands Bart J. J. M. van den Hurk Royal Netherlands Meteorological Institute KNMI, De Bilt, The Netherlands J. (Hans) van der Kwast Afdeling Teledetectie en Aardobervatieprocessen, VITO, Mol, Belgium Roderik van de Wal Institute of Marine and Atmospheric Research Utrecht (IMAU), Faculty of Science, Utrecht University, The Netherlands