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

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.