Detecting changes in winter precipitation extremes and fluvial flood risk

There is a widely held perception that flood risk has increased across Europe during the last decade (EEA, 2005). Following extensive flash flooding in England, the Pitt Review (2008) concluded that: “The Summer 2007 floods cannot be attributed directly to climate change, but they do provide a clear indication of the scale and nature of the severe weather events we may experience as a result”. The review further asserted that, “timely decisions will allow organisations the flexibility to choose the most cost-effective measures, rather than being forced to act urgently and reactively. Early action will also avoid lock-in to long-lived assets such as buildings and infrastructure which are not resilient to the changing climate”..

Climate change impacts on Yangtze River discharge at the Three Gorges Dam

The Yangtze River basin is home to more than 400 million people and contributes to nearly half of China's food production. Therefore, planning for climate change impacts on water resource discharges is essential. We used a physically based distributed hydrological model, Shetran, to simulate discharge in the Yangtze River just below the Three Gorges Dam at Yichang (1007200km2), obtaining an excellent match between simulated and measured daily discharge, with Nash–Sutcliffe efficiencies of 0.95 for the calibration period (1996–2000) and 0.92 for the validation period (2001–2005). We then used a simple monthly delta change approach for 78 climate model projections (35 different general circulation models – GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to examine the effect of climate change on river discharge for 2041–2070 for Representative Concentration Pathway 8.5. Projected changes to the basin's annual precipitation varied between −3.6 and +14.8% but increases in temperature and consequently evapotranspiration (calculated using the Thornthwaite equation) were projected by all CMIP5 models, resulting in projected changes in the basin's annual discharge from −29.8 to +16.0%. These large differences were mainly due to the predicted expansion of the summer monsoon north and west into the Yangtze Basin in some CMIP5 models, e.g. CanESM2, but not in others, e.g. CSIRO-Mk3-6-0. This was despite both models being able to simulate current climate well. Until projections of the strength and location of the monsoon under a future climate improve, large uncertainties in the direction and magnitude of future change in discharge for the Yangtze will remain

Characterizing uncertainty of the hydrologic impacts of climate change

The high climate sensitivity of hydrologic systems, the importance of those systems to society, and the imprecise nature of future climate projections all motivate interest in characterizing uncertainty in the hydrologic impacts of climate change. We discuss recent research that exposes important sources of uncertainty that are commonly neglected by the water management community, especially, uncertainties associated with internal climate system variability, and hydrologic modeling. We also discuss research exposing several issues with widely used climate downscaling methods. We propose that progress can be made following parallel paths: first, by explicitly characterizing the uncertainties throughout the modeling process (rather than using an ad hoc “ensemble of opportunity”) and second, by reducing uncertainties through developing criteria for excluding poor methods/models, as well as with targeted research to improve modeling capabilities. We argue that such research to reveal, reduce, and represent uncertainties is essential to establish a defensible range of quantitative hydrologic storylines of climate change impacts

Detecting Changes in Winter Precipitation Extremes and Fluvial Flood Risk

There is a widely held perception that flood risk has increased across Europe during the last decade (EEA, 2005). Following extensive flash flooding in England, the Pitt Review (2008) concluded that: “The Summer 2007 floods cannot be attributed directly to climate change, but they do provide a clear indication of the scale and nature of the severe weather events we may experience as a result”. The review further asserted that, “timely decisions will allow organisations the flexibility to choose the most cost-effective measures, rather than being forced to act urgently and reactively. Early action will also avoid lock-in to long-lived assets such as buildings and infrastructure which are not resilient to the changing climate”..