Zbigniew W. Kundzewicz

The implications of projected climate change for freshwater resources and their management

A review of the implications of climate change for freshwater resources, based on Chapter 4 of Working Group 2, IPCC.

Climate change. Stationarity is dead: whither water management?

Climate change undermines a basic assumption that historically has facilitated management of water supplies, demands, and risks.

Change detection in hydrological records—a review of the methodology / Revue méthodologique de la détection de changements dans les chroniques hydrologiques

Abstract Abstract General guidance is offered as to the methodology of change detection in time series of hydrological data, embracing stages such as preparing a suitable data set, exploratory analysis, application of adequate statistical tests and interpretation of results. Although the paper cannot go into full details of the many existing tests, it gives an easy-to-follow overview, offering practical hints and describing caveats and misconceptions. It serves as a refresher, raising attention to essential things that have often been ignored. A particular recommendation of the paper is that greater use of distribution-free testing methods, particularly resampling methods, should be made. These methods are recommended because they are particularly suited to hydrological data, which are often strongly skewed (non-normal), seasonal and serially correlated. Resampling techniques are flexible, robust and powerful, and require only minimal assumptions to be made about the data.

Flood risk and climate change: global and regional perspectives

Abstract A holistic perspective on changing rainfall-driven flood risk is provided for the late 20th and early 21st centuries. Economic losses from floods have greatly increased, principally driven by the expanding exposure of assets at risk. It has not been possible to attribute rain-generated peak streamflow trends to anthropogenic climate change over the past several decades. Projected increases in the frequency and intensity of heavy rainfall, based on climate models, should contribute to increases in precipitation-generated local flooding (e.g. flash flooding and urban flooding). This article assesses the literature included in the IPCC SREX report and new literature published since, and includes an assessment of changes in flood risk in seven of the regions considered in the recent IPCC SREX report—Africa, Asia, Central and South America, Europe, North America, Oceania and Polar regions. Also considering newer publications, this article is consistent with the recent IPCC SREX assessment finding that the impacts of climate change on flood characteristics are highly sensitive to the detailed nature of those changes and that presently we have only low confidence1 in numerical projections of changes in flood magnitude or frequency resulting from climate change. Editor D. Koutsoyiannis Citation Kundzewicz, Z.W., et al., 2013. Flood risk and climate change: global and regional perspectives. Hydrological Sciences Journal, 59 (1), 1–28.

Are climate models ready for prime time in water resources management applications, or is more research needed?

Citation Kundzewicz, Z. W. & Stakhiv, E. Z. (2010) Are climate models “ready for prime time” in water resources management applications, or is more research needed? Editorial. Hydrol. Sci. J. 55(7), 1085–1089.

Historical hydrology for studying flood risk in Europe

Abstract Historical hydrology can be defined as a research field occupying the interface between hydrology and history, with the objectives: to reconstruct temporal and spatial patterns of river flow and, in particular, extreme events (floods, ice phenomena, hydrological droughts) mainly for the period prior to the creation of national hydrological networks; and to investigate the vulnerability of past societies and economies to extreme hydrological events. It is a significant tool for the study of flood risk. Basic sources of documentary data on floods and methods of data collection and analysis are discussed. Research progress achieved in Europe in reconstructing past runoff conditions, hydrological and hydraulic analyses of historical floods, their meteorological causes, impacts and relation to climate change, as well as use of combined series of palaeofloods, instrumental and historical floods for reconstructing long-term flood records, is reviewed. Finally, the future research needs of historical hydrology are discussed.

Trend detection in river flow series: 1. Annual maximum flow / Détection de tendance dans des séries de débit fluvial: 1. Débit maximum annuel

Abstract Results of a study on change detection in hydrological time series of annual maximum river flow are presented. Out of more than a thousand long time series made available by the Global Runoff Data Centre (GRDC) in Koblenz, Germany, a worldwide data set consisting of 195 long series of daily mean flow records was selected, based on such criteria as length of series, currency, lack of gaps and missing values, adequate geographical distribution, and priority to smaller catchments. The analysis of annual maximum flows does not support the hypothesis of ubiquitous growth of high flows. Although 27 cases of strong, statistically significant increase were identified by the Mann-Kendall test, there are 31 decreases as well, and most (137) time series do not show any significant changes (at the 10% level). Caution is advised in interpreting these results as flooding is a complex phenomenon, caused by a number of factors that can be associated with local, regional, and hemispheric climatic processes. Moreover, river flow has strong natural variability and exhibits long-term persistence which can confound the results of trend and significance tests.

Will groundwater ease freshwater stress under climate change

Abstract Today, groundwater is the source of about one third of global water withdrawals and provides drinking water for a large portion of the global population. In many regions it is subject to stress with respect to both quantity and quality. Hence, it is of utmost importance to improve our knowledge about the impacts of climate change on groundwater. Climate change will affect groundwater recharge, i.e. long-term average renewable groundwater resources, via increases in mean temperature, precipitation variability and sea level, as well as via changes in mean precipitation (increasing in some areas and decreasing in others). Over many areas groundwater recharge is projected to increase in the warming world (though less than river runoff), but many semi-arid areas that suffer from water stress already may face decreased groundwater recharge. The sea level rise that is likely to occur during the 21st century might leave many flat coral islands without a reliable groundwater source. However, in coastal areas with a land surface elevation of a few metres or more, groundwater availability is more strongly impacted by changes in groundwater recharge than sea-level rise. Under climate change, reliable surface water supply is likely to decrease due to increased temporal variations of river flow that are caused by increased precipitation variability and decreased snow/ice storage. Under these circumstances, it might be beneficial to take advantage of the storage capacity of groundwater and increase groundwater withdrawals. However, this option is only sustainable where groundwater withdrawals remain well below groundwater recharge. Groundwater is not likely to ease freshwater stress in those areas where climate change is projected to decrease groundwater recharge (e.g. Northeast Brazil and the Mediterranean basin).

Flood protection and management: quo vadimus?

In the last decade, there have been many destructive floods in various parts of the world. Despite the extensive investment in flood control works, neither flood occurrences nor damages are decreasing. A possible consequence of climate change is an increased frequency of extreme meteorological events that may cause floods. Discussion is offered of some recent large floods in the world and of the experiences in combating floods in Japan. Floods change over time as societies change. There is no single universal remedy against floods and site-specific local efforts are necessary. It is essential to undertake damage mitigation measures together with physical control measures for flood management in an integrated approach, using a mixture of structural and non-structural means. A more disaster conscious society needs to be built with better preparedness and safe-fail (safe in failure) rather than, unrealistic, fail-safe (safe from failure) design of flood defences.

Large floods in Europe, 1985–2009

Abstract The paper looks at two metrics of flood events: flood severity (related to flood frequency) and flood magnitude (related to flood severity, as above, but also to flood duration and affected area). A time series of flood information, over 25 years, collected by the Dartmouth Flood Observatory, is used to describe the spatio-temporal variability of large floods in Europe. Direct factors responsible for changes in flood severity and magnitude over time may be related to both climate and ground surface changes. Indirect links between flood severity/magnitude and socio-economic indices occur via flood risk reduction activities, land-use change and land-cover change. The present analysis shows an increasing trend during the 25-year period in the number of reported floods exceeding severity and magnitude thresholds. Editor D. Koutsoyiannis Citation Kundzewicz, Z.W., Pińskwar, I., and Brakenridge, G.R., 2013. Large floods in Europe, 1985–2009. Hydrological Sciences Journal, 58 (1), 1–7.