Kashmir floods 2014, credit: EPA March 20, 2019 | Floodwater in - PowerPoint PPT Presentation

Kashmir floods 2014, credit: EPA

March 20, 2019 | Floodwater in Hamburg, Iowa, USA. (Scott Olson/Getty Images)

Lecture aims: to provide an overview of: • the different characteristics of flood events and how they are changing • the drivers of changing flood risk Somerset Levels, Matt Cardy/ Getty Images, Feb 2014

Magnitudes Frequency Seasonality Extent Water management Climate Land cover Geomorphology Populations

Magnitudes Frequency Seasonality Extent II. Why is global flood risk changing? Water management Climate Land cover Geomorphology Populations

Streamflow (ft 3 /s) Red circles: annual maxima Source: stream hydrograph of the Raccoon River, Iowa, by G. Villarini

Slater and Villarini (2016). Recent trends in US flood risk. Geophysical Research Letters , 43(24).

Do et al. (2017). A global-scale investigation of trends in annual maximum streamflow. Journal of hydrology , 552 , 28-43.

Frequency projected change in the 100-year flood (20 th C into the 21 st C), under the RCP8.5 scenario Magnitude consistency in the change in the magnitude of the estimated 100-year flood under SRES A1b emissions in 2050, for 7 climate models (% of the total number of models) [ left ] Hirabayashi et al. (2013), Nature Climate Change , 3 (9), p.816 [ right ] Arnell and Gosling (2016), Climatic Change , 134 (3), 387-401.

Flood seasonality is when floods occur throughout the year Blöschl et al. (2017). Changing climate shifts timing of European floods. Science 357, 588 – 590

Northeastern Europe Annual timing of river floods (1960-2010) North Sea Western Europe – Atlantic coast Mediterranean coast Blöschl et al. (2017). Changing climate shifts timing of European floods. Science 357, 588 – 590

Berghuijs et al. (2018). Growing Spatial Scales of Synchronous River Flooding in Europe. Geophysical Research Letters , 46 (3), 1423-1428.

Flood extent varies regionally by over an order of magnitude… … and has grown by about 50% in the last 50 years Berghuijs et al. (2018). Growing Spatial Scales of Synchronous River Flooding in Europe. Geophysical Research Letters , 46 (3), 1423-1428.

I. How are flood characteristics changing? Magnitudes Frequency Extent Seasonality Water management Climate change and variability Land cover change Geomorphic change Population change

Grill et al. (2019). Mapping the world’s free -flowing rivers. Nature , 569 (7755), 215.

Snowmelt Extreme precipitation Soil moisture excess Berghuijs et al. (2019). The relative importance of flood generating mechanisms across Europe. Water Resources Research.

Historical probability of flood hazard during El Niño in February (110 year climatology) Emerton, Cloke, et al. (2017). Complex picture for likelihood of ENSO-driven flood hazard. Nature communications , 8 , 14796.

Influence of tropical cyclones (TCs) on rainfall (Khouakhi, 2017) Lines: TC tracks Dots: rain gauges There has been an increase in the number of major storms (Emanuel, 2017) and a global slowdown of their translation speed (Kossin, 2018) Khouakhi et al. (2017). Contribution of tropical cyclones to rainfall at the global scale. Journal of Climate , 30 (1), 359-372.

Zhang et al. (2018). Urbanization exacerbated the rainfall and flooding caused by hurricane Harvey in Houston. Nature , 563 (7731), 384.

Slater, L.J., Singer, M.B., Kirchner J.W. (2015) Hydrologic versus geomorphic drivers of trends in flood hazard, Geophysical Research Letters .

• The global exposed flood area has barely increased • BUT the exposed population and exposed assets both have. Change in population distribution since 1960 (persons) Tanoue, M., Hirabayashi, Y., & Ikeuchi, H. (2016). Global-scale river flood vulnerability in the last 50 years. Scientific reports , 6, 36021.

➢ Our understanding of the different characteristics of fluvial flooding has grown rapidly in recent decades. ➢ Flood characteristics are nonstationary : their magnitude, frequency, extent and seasonality may shift. ➢ However, disentangling the different drivers of flood risk (water management, climatic drivers, land cover, geomorphology, population) is still a major global challenge.

Arnell and Gosling (2016). The impacts of climate change on river flood risk at the global scale. Climatic Change , 134 (3), 387-401. Berghuijs et al. (2018). Growing Spatial Scales of Synchronous River Flooding in Europe. Geophysical Research Letters , 46 (3), 1423-1428. Berghuijs et al. (2019). The relative importance of flood generating mechanisms across Europe. Water Resources Research. Blöschl et al. (2017). Changing climate shifts timing of European floods. Science 357, 588 – 590 Do et al. (2017). A global-scale investigation of trends in annual maximum streamflow. Journal of hydrology , 552 , 28-43. Emerton et al. (2017). Complex picture for likelihood of ENSO-driven flood hazard. Nature communications , 8 , 14796. Grill et al. (2019). Mapping the world’s free -flowing rivers. Nature , 569 (7755), 215. Khouakhi et al. (2017). Contribution of tropical cyclones to rainfall at the global scale. Journal of Climate , 30 (1), 359-372. Hirabayashi et al. (2013). Global flood risk under climate change, Nature Climate Change , 3 (9), p.816. Sharma et al. (2018). If precipitation extremes are increasing, why aren't floods? Water Resources Research , 54 (11), 8545-8551. Slater et al. (2015). Hydrologic versus geomorphic drivers of trends in flood hazard, Geophysical Research Letters , 42 (2), 370-376. Slater and Villarini (2016). Recent trends in US flood risk. Geophysical Research Letters , 43(24). Tanoue et al. (2016). Global-scale river flood vulnerability in the last 50 years. Scientific reports , 6 , 36021. Zhang et al. (2018). Urbanization exacerbated the rainfall and flooding caused by hurricane Harvey in Houston. Nature , 563 (7731), 384.