The influence of multiyear drought on the annual rainfall-runoff relationship: An Australian perspective

• Published in: Water resources research Vol. 51; no. 4; pp. 2444 - 2463
• Main Authors: Saft, Margarita, Western, Andrew W., Zhang, Lu, Peel, Murray C., Potter, Nick J.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-04-2015; John Wiley & Sons, Inc
• Subjects: Adaptation; Annual; Annual rainfall; Annual runoff; Anomalies; Atmospheric precipitations; Australia; Catchment area; Catchment scale; Catchments; Climate; Climate change; Climate variability; Climatic conditions; decadal climate variability; Drought; Dry periods; Genetic transformation; hydrologic nonstationarity; Hydrologic processes; Hydrology; Length; Linkages; millennium drought; Precipitation; Precipitation anomalies; Properties; Rain; Rainfall; rainfall-runoff relationship; Rainfall-runoff relationships; Runoff; Statistical analysis; Stream discharge; Stream flow; streamflow; Variability; Australia
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2014WR015348

Most current long‐term (decadal and longer) hydrological predictions implicitly assume that hydrological processes are stationary even under changing climate. However, in practice, we suspect that changing climatic conditions may affect runoff generation processes and cause changes in the rainfall‐runoff relationship. In this article, we investigate whether temporary but prolonged (i.e., of the order of a decade) shifts in rainfall result in changes in rainfall‐runoff relationships at the catchment scale. Annual rainfall and runoff records from south‐eastern Australia are used to examine whether interdecadal climate variability induces changes in hydrological behavior. We test statistically whether annual rainfall‐runoff relationships are significantly different during extended dry periods, compared with the historical norm. The results demonstrate that protracted drought led to a significant shift in the rainfall‐runoff relationship in ∼46% of the catchment‐dry periods studied. The shift led to less annual runoff for a given annual rainfall, compared with the historical relationship. We explore linkages between cases where statistically significant changes occurred and potential explanatory factors, including catchment properties and characteristics of the dry period (e.g., length, precipitation anomalies). We find that long‐term drought is more likely to affect transformation of rainfall to runoff in drier, flatter, and less forested catchments. Understanding changes in the rainfall‐runoff relationship is important for accurate streamflow projections and to help develop adaptation strategies to deal with multiyear droughts.
Key Points:
Multiyear droughts can change catchment hydrological behavior
Long dry periods can result in higher runoff reductions than single year droughts
Drier, flatter, and less forested catchments are more susceptible to change