Increasing risk of great floods in a changing climate

Abstract

Radiative effects of anthropogenic changes in atmospheric composition are expected to cause climate changes, in particular an intensification of the global water cycle with a consequent increase in flood risk. But the detection of anthropogenically forced changes in flooding is difficult because of the substantial natural variability; the dependence of streamflow trends on flow regime further complicates the issue. Here we investigate the changes in risk of great floods--that is, floods with discharges exceeding 100-year levels from basins larger than 200,000 km(2)--using both streamflow measurements and numerical simulations of the anthropogenic climate change associated with greenhouse gases and direct radiative effects of sulphate aerosols. We find that the frequency of great floods increased substantially during the twentieth century. The recent emergence of a statistically significant positive trend in risk of great floods is consistent with results from the climate model, and the model suggests that the trend will continue.

A safe operating space for humanity

“…Observations of a climate transition include a rapid retreat of summer sea ice in the Arctic Ocean (Johannessen 2008), retreat of mountain glaciers around the world (IPCC 2007a), loss of mass from the Greenland and West Antarctic ice sheets (Cazenave 2006), an increased rate of sea-level rise in the last 10-15 years (Church and White 2006), a four-degree latitude pole-ward shift of subtropical regions (Seidel and Randel 2006), increased bleaching and mortality in coral reefs (Bellwood et al 2004;Stone 2007), a rise in the number of large floods (Milly et al 2002;MEA 2005a), and the activation of slow feedback processes like the weakening of the oceanic carbon sink (Le ).…”

Climate change: a ‘glocal’ problem requiring ‘glocal’ action

“…Changing precipitation patterns can affect agricultural potential and thus food and water security. In addition, changing weather patterns and increased extreme event frequency could cause more large scale flooding (Milly et al 2002) and possibly droughts and storms (Emanuel 2005) with national consequences. Rising sea levels threaten low-lying coastal zones, which are the most densely inhabited and developed areas.…”

Global projections of changing risks of floods and droughts in a changing climate

“…flood and drought, estimated using the daily modelled discharge by the MIROC. The global warming simulation with relatively high spatial resolution of the MIROC will provide a detailed picture of future extremes in river discharge, even over small basins that have not been distinguished by Milly et al (2002). It is essential to show projections of changes in extreme discharge under global warming using daily discharge data, since previous studies discussed future projections on water-related disasters mainly in terms of changes in monthly means of precipitation or in discharge.…”

“…This is primarily because of the limitation of spatial resolution in general circulation models (GCMs). Milly et al (2002) investigated changes in flood extremes using monthly river discharge data for both gauge observations and GCM simulations. They found that the risk of great floods increased during the 20th century, mainly over the northern high latitudes, and that this increase may continue.…”