Partitioning the effects of pine plantations and climate variability on runoff from a large catchment in southeastern Australia

Abstract

Effects of substantial increase in area of pine plantations from 1960 to 2000 on runoff in a large catchment in southeastern Australia are quantified. Reliable land use maps were prepared for 1960–1979, 1980–1989, and 1990–2000 conditions from various data sources. Land use changes in the subcatchments have occurred at varying rates (16 to 28%) with pines replacing pasture and native woody vegetation. On the basis of long‐term trends in rainfall‐runoff relationships, flow duration curves, and history of land use changes, it is shown that there is strong evidence of reduction in runoff over a wide range. Modeling methodology using a lumped catchment‐scale rainfall‐runoff model (SMAR) and landscape‐scale ecohydrological models (CLASS U3M‐1D, CLASS PGM, and 3PG+) was implemented in a catchment framework to partition the effects of land use change and climate variability during 1960–2000. Runoff reductions from land use change in the range 22–52 mm/yr are estimated for different subcatchments. Annual yield impact per 10% of the catchment forested (AYI/10%) from catchment‐scale modeling is estimated to vary between 14.3 to 19.2 mm/yr for the subcatchments. AYI/10% from landscape‐scale modeling is estimated to vary between 12.8 to 21.3 mm/yr.