Review of Floods in a Changing Climate: Extreme Precipitation by Ramesh S. V. Teegavarapu

In July 2010, Pakistan suffered the worst flooding, in its Indus River basin, it ever experienced. More than a fifth of the country’s land area was inundated, between 15 and 20 million people were displaced, and about 2,000 people perished. Economic damage resulting from this event is estimated at approximately US$8–10 billion (World Bank 2010). The Indus basin has been frequently hit by floods during the monsoon season. In August 2013, another flash flood resulted in the death of 180 people. Between July and mid-August, unusually heavy rainfall in the transboundary Amur River watershed resulted in massive flooding in both China and Russia. More than 60,000 people were affected in China and over 787,000 ha of farm land were submerged. In Russia, the flooding is considered to be the worst in 120 years. In the United States, catastrophic flooding in Colorado in early September affected 17 counties; and 430 mm resulted in economic damages estimated at over US$1 billion; and 430 mm of rain (close to its annual precipitation of 525 mm) fell over Boulder County in just 7 days. Earlier during the year, on June 20, 2013, heavy rainfall in Alberta, Canada, caused some of the worst flooding in the province’s history. More than 100,000 people were displaced and economic damage is estimated to exceed Can$5 billion. On the other side of the Atlantic, in central Europe, heavy rains caused massive flooding, with damages estimated at approximately US$3.9 billion. On March 30, 2013, 152 mm of rain (equivalent to 70% of March’s average precipitation) fell on Port Louis, the capital of Mauritius, in less than 2 h. Within minutes, roads were transformed into rivers, causing a huge traffic jam and paralyzing the economic center of the island. Residents were not warned of the possibility of heavy rainfall on that day; the flooding claimed the lives of 11 people.

Devastating flash floods seem to be happening very frequently and on every continent. Is it really the case, or does it seem that they are becoming more and more frequent as a result of efficient reporting by the media? Are these extreme precipitation events a result of climate change? Regardless, the latter is the first to bear the brunt.

From a scientific standpoint, rising atmospheric temperature owing to global warming will result in higher evaporation and an increase in the water-holding capacity of the atmosphere. This may lead to an intensification of the hydrologic cycle resulting in a change in the frequency, intensity, spatial extent, duration, and timing of extreme precipitation events, evapotranspiration, tropospheric water content, and runoff (National Research Council 2011). Changes in precipitation extremes can be in the following three ways: (1) a shift in the mean, resulting in less low magnitude events and more high magnitude events; (2) an increase in variability, i.e., more low and high magnitude events; and (3) a change in the shape of the distribution, i.e., near-constant low-magnitude events but an increase in high-magnitude events [Intergovernmental Panel on Climate Change (IPCC) 2012].

Because it is known with a high degree of confidence that a rise in the concentration of greenhouse gases in the atmosphere influences the climate and subsequently the hydrological cycle, frequent occurrences of flash floods are probably the effect of climate change. Although this hypothesis is valid, it is still hard to pin any one particular event and state with certainty that it is a result of climate change, or had the climate not been changing, that particular event would not have happened. Research in this area is extremely important and may help to unravel the reason behind the seeming increase in the number of flood events. Marvel and Bonfils (2013), for example, demonstrated that changes in land and ocean precipitation predicted by the global warming theory are indeed occurring, even though they are hard to detect in observational records. Internal variability in the atmospheric system accounts for only part of the changes detected. The other factor responsible for this change is external and probably anthropogenic.

Teegavarapu’s Floods in a Changing Climate: Extreme Precipitation is therefore extremely timely. The 269-page book is divided into nine chapters covering almost everything from the basics of precipitation and climate change to modeling and future direction in this area.

Chapter 1 of the book gives an overview of climate change and variability, the precipitation process and how it can lead to floods, and the influence of climate change and climate variability. It also describes the main issues pertaining to extreme precipitation in the context of a changing climate. Chapter 2 covers precipitation measurement techniques. Ground-, radar-, and satellite-based measurements are discussed. Both chapters are well-written and provide a good introduction of the topic and how it is relevant in the context of climate change.

On a temporal scale, a flood is one event that has a duration, frequency, and return-period. On the ground, however, the event is spatial in nature, covering anything from a few ${\mathrm{km}}^2$ to counties and can even be transboundary. Therefore, spatial analysis of precipitation is important. This topic is covered in Chapter 3—the longest chapter in the book. Teegavarapu presents a summary of almost every technique available. The techniques include both classical approaches and emerging techniques, and some are illustrated with pertinent examples. This chapter is extremely detailed and can be a valuable reference guide.

Analysis of extreme precipitation and floods is presented in Chapter 4. This chapter discusses the hydrometeorological aspects of precipitation and floods. Flood mechanisms and the role and effect of shallow groundwater and soil moisture are explained. Cyclone-related flooding, which some argue is becoming more frequent as a result of climate change, is also presented.

General circulation models (GCMs) and hydrological models often run at different temporal and spatial scales. To perform hydrological forecasts based on climate projections, climate model outputs have to be downscaled and reconciled with hydrological model. Different statistical and dynamical downscaling methods have been developed. The main steps in the process include the selection of predictors that influence the meteorological variables of interest, selecting the most efficient downscaling technique and developing a model, and correcting for biases resulting from uncertainties in the GCM outputs. Details of downscaling techniques summarized from the Canadian Institute for Climate Studies (CICS 2006) and Wilby et al. (2004) are provided in Chapter 5. The chapter is a good synopsis of recently developed downscaling techniques.

Large-scale circulation patterns are known to have a strong modulating effect on local-hydrometeorological variables, especially precipitation. In fact, a number of flood events have been linked to climate teleconnection patterns. Chapter 6 discusses the influence of such climate variability and their influence on precipitation. The author focuses on two major teleconnections—the Atlantic Multidecadal Oscillation (AMO) and the El Niño Southern Oscillation (ENSO)—both notorious for their effect on precipitation patterns in the eastern United States. A discussion on other climate variability patterns such as the Pacific Decadal Oscillation (PDO) and the Indian Ocean Dipole (IOD) would have benefitted readers around the world.

Teegaverapu further discusses precipitation variability and trends in Chapter 7. The discussion includes historical and projected trends in precipitation, both globally and in the United States. Statistical techniques, both parametric and nonparametric, for the identification of trends in extreme events are presented. This chapter is a good summary of techniques currently employed in variability and trend analysis.

Often, the challenge the practicing community (engineers, planners, and policy makers) faces is that academic research is not translated into a form that can be applied in practice. It is hard to sift through the bulk of academic literature (some of which is not even accessible to practitioners) and select the most appropriate technique. Recognizing this limitation, the author gives a summary of the emerging trends in hydrologic design of extreme precipitation and presents an example of the design of a storm sewer system to accommodate the projected effect of climate change. This is a very useful chapter, and the example is pertinent.

In Chapter 9, the author concludes with a note on future perspectives on hydrologic engineering and practice.

Extreme precipitation analysis is not new to the hydrological science community. Substantial research has been conducted in this field. Most of the works, if not all, assume stationarity; but with climate change, stationarity is dead (Milly et al. 2008)! The ongoing and projected changes in hydrological extremes will have a profound impact on infrastructure design practices, especially because most hydraulic structures, ranging from roadside drains to levees, are designed based on extreme events and their return periods. In the United States, for example, Bulletin 17 (17B updated in 1982) is undergoing a much needed revision to incorporate the influence of climate variability and change (Griffis and Stedinger 2007; Stedinger and Griffis 2011). Similarly, engineering standards around the world will have to be reassessed to see if they are still applicable and, where required, modified to accommodate projected climate change effects (Khedun and Singh 2013). To this end, Teegavarapu’s contribution is welcomed. The book is well written and reflects the author’s extensive experience in the analysis of extreme precipitation. It is a much needed addition to the library of academics and practitioners alike.