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This review provides a broad overview of the current state of flood research, current challenges, and future directions. Beginning with a discussion of flood-generating mechanisms, the review synthesizes the literature on flood forecasting, multivariate and nonstationary flood frequency analysis, urban flooding, and the remote sensing of floods. Challenges and future flood research directions are outlined and highlight emerging topics where more work is needed to help mitigate flood risks. It is anticipated that the future urban systems will likely have more significant flood risk due to the compounding effects of continued climate change and land-use intensification. The timely prediction of urban floods, quantification of the socioeconomic impacts of flooding, and developing mitigation strategies will continue to be challenging. There is a need to bridge the scales between model capabilities and end-user needs by integrating multiscale models, stakeholder input, and social and citizen science input for flood monitoring, mapping, and dissemination. Although much progress has been made in using remote sensing for flood applications, recent and upcoming Earth Observations provide excellent potential to unlock additional benefits for flood applications. The flood community can benefit from more downscaled, as well as ensemble scenarios that consider climate and land-use changes. Efforts are also needed for data assimilation approaches, especially to ingest local, citizen, and social media data. Also needed are enhanced capabilities to model compound hazards and assess as well as help reduce social vulnerability and impacts. The dynamic and complex interactions between climate, societal change, watershed processes, and human factors often confronted with deep uncertainty highlights the need for transdisciplinary research between science, policymakers, and stakeholders to reduce flood risk and social vulnerability

The magnitudes of peak streamflows and their return periods are important considerations in infrastructure design and hazard mitigation. Periods of high floods are usually associated with s...

Mauritius suffers from chronic water shortages that can severely impact its economy and the well-being of its population. Both surface and groundwater availability are determined by rainfall, which is in turn influenced by large-scale circulation patterns such as the El Nino Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Here we report on the influence of these two teleconnection patterns and present the result of a simple neural network for precipitation forecasting, based on the state of ENSO and IOD. Data from the Vacaos station, for the period 1961 to 2012 is used. We found statistically significant correlation between average winter rainfall and ENSO and IOD indices. The correlation for summer was negligible. The prediction of summer precipitation was less accurate than that of winter precipitation. The findings from this study can help in more efficient planning and management of water resources on the island.

[1] The influence of two large-scale circulation patterns (the El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO)), and the effect of the interdecadal modulation of ENSO on precipitation in the state of Texas, U.S., was explored. Texas, by virtue of its size, topography, and geographical location, spans a wide range of climatic regions. The state is divided into 10 climate divisions. The precipitation pattern in each division follows different probability distributions. The climate regimes which trigger this difference are discussed. The seasonal correlation between ENSO and PDO with precipitation anomaly in each climate division was established. Copula-based models were developed to examine the dependence structure between the large-scale climate indices and average monthly seasonal precipitation. The choice of copula is discussed in light of the dependence structure. The selected copulas were then used to simulate precipitation anomalies in three climate divisions: one which has a semiarid climate, one located in the wettest region, and one straddling the subtropical humid and subtropical subhumid regions of the state. The statistical performance of bivariate models for ENSO and precipitation, and trivariate models for ENSO, PDO, and precipitation, in simulating precipitation anomalies were compared. In general, inclusion of PDO was found to improve simulation results. The most notable improvement was in simulating negative precipitation anomalies during La Nina and negative PDO. The copula models were also tested for their abilities to predict precipitation anomalies in these three regions. Again, the trivariate models performed better, especially in predicting droughts due to La Nina and negative PDO.

Climate change is a phenomenon affecting the whole planet; however, its impacts are mostly felt by those who are already deprived—low—income countries and regions prone to climate related disasters. The occurrence, intensity, and spatial extent of hydrological extremes are likely to change with global warming. This paper reviews current and future impacts of a changing climate on the hydrological cycle and how it affects floods; droughts and related impacts on agriculture and food availability; sea-level rise and its impacts on coastal communities; and waterborne, rodent-borne, and vector-borne diseases. The effect of climate on quality of life and risks of conflicts is also explored. Regions that are most likely to be impacted by each are highlighted. The disasters associated with climate change are very similar to those that the world has periodically witnessed due to climate variability patterns, such as the El Nino Southern Oscillation. However, their frequency and severity may be much higher and they may compromise efforts currently underway to solve existing problems.

The identification and prediction of drought events depend on the integrity of the dataset employed. Streamflow is a good indicator of surface water availability and has dominated the literature on frequency analysis of hydrological droughts and water management. However, gauged measurements are impaired by climate and land use changes, especially in large, modified watersheds. Hence, their use in drought prediction is limited because they may violate the assumption of stationarity unless a naturalized observation series is obtained. In this paper, a land surface model is used to generate runoff in the Rio Grande/Rio Bravo del Norte basin. Land use land cover is kept constant so that changes are a result of climatological variations. The river threads across several climatic zones; therefore the basin is divided into different regions for analysis. Using statistical theory of runs, water deficit duration and severity and drought interarrival time are extracted from 3-month Standardized Runoff Inde...

Daily discharge volumes of Comal Springs, the largest artesian spring of the Edwards Aquifer (EA) in Central Texas, were utilized to characterize the flow of Comal Springs for the period of record spanning 1933–2007. The influence of water extraction (pumping) on discharge characteristics during the record was examined and found to be statistically significant for both volume and variability of spring discharge (p < 0.01). Pumping explains approximately a quarter of the variation in annual discharge (r2 = 0.25) and nearly a third of the daily variability (r2 = 0.32) within the Comal Springs discharge record. Statistically significant teleconnections to flow are demonstrated within the discharge record of Comal Springs. The El Nino-Southern Oscillation (ENSO, as measured by the Southern Oscillation Index) and the Pacific Decadal Oscillation (PDO) are shown to exhibit statistically significant correlations with annual mean flow from Comal Springs. PDO modulation of ENSO results in mean flow anomalies of 21.9% between extreme quintile years. The Atlantic Multi-decadal Oscillation (AMO) appears to exert influence based on the magnitude of the index value, irrespective of its positive or negative condition (p < 0.01), with the highest quintile (based on magnitude) years correlating with strong positive flow anomalies. A composite index was developed which combines the AMO, PDO and SOI. The extreme quintile years of this index demonstrate a 32.4% divergence in flow (p < 0.01) while demonstrating a stronger skill at capturing negative flow anomalies than positive anomalies. Precipitation data, at 4-km spatial resolution, were utilized to examine the temporal and spatial correlation of water input to the EA with rates of average monthly discharge from Comal Springs. The spatial dependence of the correlation between precipitation and Comal Springs discharge indicates significant seasonal variability. Overall, the correlation between precipitation and discharge is significant for spring, summer and fall seasons and not significant for winter. Copyright © 2009 Royal Meteorological Society

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 km 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

Water is the most precious natural resource on the earth. The amount of water available on the earth is limited and some regions are already heading toward water bankruptcy. Rising population, climate change, conversion of agricultural land for biofuel production, etc. further complicate the problem of adequate water allocation. The problem can be even more complex in transboundary river basins. This article presents the current state of water around the world and explores impending water challenges.

Recent years have witnessed an increase in global average air temperatures as well as ocean temperatures, as documented by the Intergovernmental Panel on Climate Change (IPCC). The rise in temperature is considered irrefutable evidence of climate change, and this has already started to have serious consequences for water resources and will have even more dire consequences in the future. Compounding these consequences are population growth, land-use changes and urbanization, increasing demands for water and energy, rising standards of living, changing dietary habits, changing agricultural practices, increasing industrial activities, increased pollution, and changing economic activities. All these will likely have adverse effects on water resources. This article briefly discusses climate change and its causes and impacts on water resources.

Water availability plays an important role in the socio-economic development of a region. It is however, subject to the influence of large-scale circulation indices, resulting in periodic excesses and deficits. An assessment of the degree of correlation between climate indices and water availability, and the quantification of changes with respect to major climate events is important for long-term water resources planning and management, especially in transboundary basins as it can help in conflict avoidance. In this study we first establish the correlation of the Pacific Decadal Oscillation (PDO) and El Nino-Southern Oscillation (ENSO) with gauged precipitation in the Rio Grande basin, and quantify the changes in water availability using runoff generated from the Noah land surface model. Both spatial and temporal variations are noted, with winter and spring being most influenced by conditions in the Pacific Ocean. Negative correlation is observed at the headwaters and positive correlation across the rest of the basin. The influence of individual ENSO events, classified using four different criteria, is also examined. El Ninos (La Ninas) generally cause an increase (decrease) in runoff, but the pattern is not consistent; percentage change in water availability varies across events. Further, positive PDO enhances the effect of El Nino and dampens that of La Nina, but during neutral/transitioning PDO, La Nina dominates meteorological conditions. Long El Ninos have more influence on water availability than short duration high intensity events. We also note that the percentage increase during El Ninos significantly offsets the drought-causing effect of La Ninas.

Growing population, higher demand for food and consequent agricultural irrigation, rising standard of living, increasing industrial activity, and expanding energy generation are putting greater pressure on our water resources, including rivers and aquifers. To satisfy these demands, most major rivers in the world have been exploited or are being exploited for their water. The exploitation of rivers has accomplished, at least partially, the intended objectives, but the environmental and ecological cost has been huge. This is nowhere more evident than in India. In recent years, human impact on the riverine systems and socioeconomic environment has become a matter of great concern. This book follows a journey rich in human interference of the kind that is seldom seen or even heard of and is a kind of a wake-up call for greater understanding and better management of riverine resources. The book is comprised of eight chapters and eight appendixes. Chapter 1 presents the purpose and perspectives of the book. Tracing the origins and development of major civilizations along rivers, the author argues that rivers had to be trained for the socioeconomic benefit of the society, entailing a twofold struggle. On one hand, there was a need to protect people from flood hazards; on the other hand, a safe water supply for domestic use and agricultural irrigation had to be ensured. This struggle led to the development of hydrotechnical installations for river training. The chapter is well written and provides many historical insights into river regulation programs and policies and the application of geology, geomorphology, engineering, and the societal considerations needed for the development of these programs. Chapter 2 introduces the region of Damodar River, a tributary of the Ganges. Beginning with a short description of the geography of the Damodar River, also known as the Deonad Nadi in its upstream sector, it discusses the physiographic factors and elaborates on the factors for choosing this river for study. The chapter goes on to discuss the landscape, geomorphic environment, culture, social space, land use, human ecology, and refugees. The chapter concludes with a statement of the objectives of the book, research paradigm, geomorphological and human environmental issues, models and methods, techniques and tools, and the organization of the book. This is a well-written chapter and provides a wealth of information that is highly useful to those engaged in river training works. Like other rivers in India, China, and other countries, the Damodar River is notorious for its calamitous floods. For protecting property and people from these floods, heavy embankments were employed in the lower reaches for reducing flood hazard in the Rarh plain. With the establishment of the Damodar Valley Corporation (DVC) in 1948, sophisticated engineering structures were constructed for river regulation and control. The result has been the rise of the riverbed, expansion of cross sections, the opening of a number of spill channels, and changes in the soil composition in the adjacent riparian tract. Considering these issues, Chapter 3 reviews the state and community-level effort in flood and water resources management and impacts of embankments, with particular focus on the hydrogeomorphic consequences of lateral control structures. Chapter 4 presents a hydrogeomorphic perspective of the consequences of control structures on the Damodar River, including reservoirs. Rivers are known to respond to anthropogenic activities through morphological and hydrological adjustments in the channel. More particularly, dams alter the flow regime, channel characteristics, and sediment supply of the river, and this same has happened to the Damodar River. This chapter discusses at length the hydrological impacts of dams, the changes in the flood behavior of the lower reaches, and changes in river morphology. The discussion is rich in empirical evidence and highly qualitative. The colonization of the lower Damodar River bed has been occurring since 1947 and is the subject of Chapter 5. Beginning with a history of colonization and the reasons behind colonization by refugees from Bangladesh, the chapter details the phases of colonization. This is one of the shorter chapters but presents those aspects that are often not considered in the water resources and engineering literature. The text is lucid and informative. The colonizing refugees use alluvial bars in the bed of Damodar River as a resource base. The riverbed landscape metamorphoses as a result of the interaction between the riverbed and its occupiers. Dealing with the controlled Lower Damodar River from a social perspective, Chapter 6 discusses the influence of culture, social pace, perceived environment, land ownership rights, and political forces on the functional relationships between the riverine environment and riparian community. The subject matter of this chapter is instructive and has a wealth of information. The controlled lower Damodar River can be perceived as a product of twin processes—hydrogeomorphic and anthropogenic land utilization—operating simultaneously. Forms, processes, and materials in the controlled reaches are not entirely natural these days, because the refugees have been playing a significant role in altering the geomorphology of the river through land use and colonization. Chapter 7 reviews a range of aspects associated with the ramifications of the interaction between the human and riverine systems. On the whole, the chapter is well written and sheds new light on the impact of humans on the river. The last chapter outlines thought for better human-environment interactions and planning approaches for future management of river resources. It argues that river regimes should be treated as economic assets, for economic and human developments are inextricably connected to the ecologically sound riverine environment. It makes a strong case for employing a mix of structural and nonstructural measures that acknowledge and incorporate local cultural attitudes, experience, and knowledge.

An understanding of the effect of climate teleconnection patterns on the hydrological cycle is important for the long term management of water resources. In this paper we examine the effect of ENSO on surface runoff in the Rio Grande basin. The watershed, which is shared between the U.S. and Mexico, is vital for the economic activities of both countries. The runoff values, obtained at 1/8° resolution, were generated by the NOAH land surface model driven using the NLDAS2 datasets for the period 1979–2008. The basin was divided into 6 distinct regions and analyzed separately. The land surface model realistically captured the hydro-climatic variations across the basin. Continuous wavelet plots of NINO 3.4, gauged rainfall and model runoff were produced and a strong correlation between ENSO and runoff was observed.

This book is volume 8 in the Comprehensive Assessment of Water Management in Agriculture series, but its scope is in no way limited to agriculture. The series editor, David Molden, sets the tone for this volume by reminding readers of water’s role in the UN’s Millennium Development Goals MDGs . The MDGs were designed to eliminate income poverty, hunger, maternal and child mortality, disease, inadequate shelter, gender inequality, and environmental degradation, and to improve global partnership http://www.un.org/millenniumgoals/ . The goals were adopted in 2000 and are set to be achieved in 2015, i.e., only five years from now http://www.undp.org/mdg/basics.shtml . It is almost certain that none of these goals can be achieved by the deadline, and it is highly unlikely that they will be achieved in the near future. Nevertheless, it is good to keep them in front of us and to keep working toward their accomplishment. Of course water is intrinsic to a number of these goals. Thus, managing water in order to provide access to the billions of people who still live without a safe source of this precious resource is crucial. River Basin Trajectories, edited by F. Molle and P. Wester, comprises 12 chapters. The editors have assembled a cluster of experts 27, including themselves who are known for their contributions in the water resources subject area to write the chapters. In chapter 1, the editors highlight human influence on watersheds. They argue that the hydrological cycle is not an independent entity; it is intertwined with the socioeconomic cycle, thus creating a hydro-social cycle. The human relationship with water, and vice versa, has not always been positive. Humans have had to deal, for example, with extreme events, such as droughts, floods, and water quality degradation. On the other hand, water resources have not always been developed and managed well. Indeed abuse and misuse of water resources is widespread throughout the world. The unambiguous link to and dependency on water have directly influenced society and have prompted an ongoing set of institutional changes. From the perspective of integrated water resources management, the watershed is the geographical unit from which everything else branches out. This ranges from surface and groundwater interaction to water quantity and quality manage

In his foreword, Professor R. L. Wilby starts with a question: How much higher does the flood wall need to be built and how much larger does the reservoir spillway need to be? This is a pertinent and practical question that needs to addressed for flood management, but its answer gets complicated by the impacts of climate change on the hydrological cycle, reflected by the changes in the rainfall and streamflow regimes as well as in the watershed physiography itself. This book attempts to present methodologies for hydrologic modeling with particular focus on impacts of climate change on flood characteristics that will help answer this question. The book comprises six chapters. Chapter 1 is introductory, providing the background of and a brief introduction to the topics covered in the book, including hydrologic models; remote sensing, geographic information systems (GIS), and digital elevation model (DEM) for hydrologic modeling; and assessment of climate change impacts. The chapter concludes with a short discussion of the organization of the book. This is a well-written chapter. Chapter 2 deals with hydrologic modeling for floods from the perspective of planning and operations related to floods. It covers lumped models, such as the unit hydrograph method, the SCS method, the rational method, empirical intelligent models, flow routing models, and commonly used watershed models. Given the limitations of space, the chapter is a good synopsis. It could have been stronger with the inclusion of some well and useful models and techniques. Since the impact of climate change is most noticeable in the cryosphere, it would have been desirable to include snowmelt models. Climate change and its impact are receiving a lot of attention these days. Chapter 3 presents methodologies for assessing hydrologic impacts due to climate change. Beginning with a discussion of emission scenarios, it goes on to discuss the projection of hydrologic impacts, dynamical downscaling approaches, statistical downscaling, disaggregation models including deterministic and stochastic techniques, macroscale hydrologic models, hypothetical scenarios for hydrologic modeling, modeling of floods under climate change, and uncertainty analysis. This is a very good chapter and contains a wealth of information. Remote sensing for hydrologic modeling constitutes the subject matter of Chapter 4. Introducing basic concepts of remote sensing that are necessary to understand and analyze images obtained by remote sensing, such as spectral reflectance for vegetation, soil, and water remote sensing platforms, it goes on to discuss digital images, including color composites and image characteristics, image rectification, image enhancement, image information extraction, land use/land cover information, utility of remote sensing for hydrologic modeling, and demonstration of image processing using MATLAB. The chapter is written in an easyto-understand manner and is a good introduction for those not well versed in remote sensing. Chapter 5 deals with GIS for hydrologic modeling. Introducing the GIS technology, the chapter discusses representation of spatial objects in GIS, proximity analysis, DEM, representation of digital data, application of digital elevation models, other sources of DEM, integration of spatial, nonspatial and ancillary data into a distributed hydrologic model, GIS and remote sensing for flood zone mapping, and web-based GIS. This is a very useful chapter and the narrative is lucid. Case studies and future perspectives constitute the subject matter of Chapter 6, the concluding chapter. Case studies include the Malaprabha reservoir catchment, India; Mahanadi River basin, India; and future perspectives. The two case studies are very illustrative. For example, the Malaprabha case study discusses streamflow projection methods, soil and water assessment tool (SWAT) and ArcView SWATmodels, study region and data used, calibration and validation of SWAT, downscaling, disaggregation, streamflow generation with SWAT, and prediction of future streamflows for changed climates. In this manner, what is discussed in the preceding chapters is brought together to bear on dealing with the case study. The Mahanadi River basin study focuses on future flood peaks and water availability and uncertainty modeling. The chapter concludes with a discussion of future perspectives. The Mujumdar and Kumar book is well written and reflects the authors’ extensive experience in hydrologic and water resources systems modeling. It will be a good addition to the library of water resources engineers, hydrologists, watershed managers, and policy makers who are concerned with the impacts of climate change. The end-of-chapter exercises, albeit few, are good. The authors state in the preface that the book synthesizes various existing methodologies that can help with planning and operational decision making under the specter of climate change. We believe the authors have largely succeeded in accomplishing this synthesis and ought to be complimented for preparing a well-written treatise on a most interesting topic—the hydrologic modeling of floods in a changing climate.