Temporal variability of climate in south‐eastern Australia: a reassessment of flood‐ and drought‐dominated regimes

Inter‐decadal periods of high and low flood activity have been considered to be the dominant factor driving river metamorphosis in catchments along the New South Wales coast. Recent work has questioned the data analysis techniques used in delineating the so‐called flood‐and drought‐dominated regimes (FDRs/DDRs). Concerns have also been raised about the validity of invoking a climatic control for river metamorphosis documented during the post‐European period, when extensive anthropogenic alteration of catchment and riparian vegetation has also occurred. This paper reviews the evolution of the FDR/DDR concept. We examine the evidence for FDRs/DDRs, and highlight problems with the original hydrological data sets, as well as with the techniques employed in the time‐series analysis. We discuss conceptual problems encountered in applying flood‐frequency analysis, and the failure of the proponents of the FDR/DDR theory to consider large‐scale climatic circulation patterns and the geographical boundaries of their influence. We conclude that the validity of the FDR/DDR notion has been seriously over‐stated, and that managing rivers on the basis that FDRs/DDRs have occurred in the past, and will continue to occur in the future, is likely to be ineffective.     

Potential Effects of Global Warming on Waterfowl Populations Breeding in the Northern Great Plains

The Prairie Pothole Region (PPR) of the Northern Great Plains is the most important breeding area for waterfowl in North America. Historically, the size of breeding duck populations in the PPR has been highly correlated with spring wetland conditions. We show that one indicator of climate conditions, the Palmer Drought Severity Index (PDSI), is strongly correlated with annual counts (from 1955 to 1996) of both May ponds (R2 = 0.72, p < 0.0001) and breeding duck populations (R2 = 0.69, p < 0.0001) in the Northcentral U.S., suggesting the utility of PDSI as an index for climatic factors important to wetlands and ducks. We then use this relationship to project future pond and duck numbers based on PDSI values generated from sensitivity analyses and two general circulation model (GCM) scenarios. We investigate the sensitivity of PDSI to fixed changes in temperature of 0°C, +1.5°C, +2.5°C, and +4.0°C in combination with fixed changes in precipitation of -10%, +0%, +7%, and +15%, changes spanning the range of typically-projected values for this region from human-induced climatic change. Most (11 of 12) increased temperature scenarios tested result in increased drought (due to greater evapotranspiration under warmer temperatures) and declining numbers of both wetlands and ducks. Assuming a doubling of CO2 by 2060, both the equilibrium and transient GCM scenarios we use suggest a major increase in drought conditions. Under these scenarios, Northcentral U.S. breeding duck populations would fluctuate around means of 2.1 or 2.7 million ducks based on the two GCMs, respectively, instead of the present long-term mean of 5.0 million. May pond numbers would fluctuate around means of 0.6 or 0.8 million ponds instead of the present mean of 1.3 million. The results suggest that the ecologically and economically important PPR could be significantly damaged by climate changes typically projected. We make several recommendations for policy and research to help mitigate potential effects.