Reconciling the dynamic relationship between climate variables and vegetation productivity into a hydrological model to improve streamflow prediction under climate change

Abstract

Anthropogenic climate change is projected to enrich the atmosphere with carbon dioxide, change vegetation dynamics and influence the availability of water at the catchment. This study combines a simple model for estimating changes in leaf area index (LAI) due to climate fluctuations with the variable infiltration capacity (VIC) land surface model to improve catchment streamflow prediction under a changing climate. The combined model was applied to thirteen gauged catchments with different land cover types (crop, pasture and tree) in the Goulburn–Broken catchment, Australia during the "Millennium Drought" (2000–2009), and two future periods (2021–2050 and 2071–2100) for two emission scenarios (RCP4.5 and RCP8.5). The future climatic and modelled streamflow results were compared with the baseline historical period of 1981–2010. This region is projected to be warmer and mostly drier in the future as predicted by 38 Coupled Model Inter-comparison Project Phase 5 (CMIP5) simulations from 15 Global Climate Models (GCMs) and for two emission scenarios. The results showed that during the Millennium Drought there was about a 30–65% reduction in mean annual runoff due to reduced rainfall and increased temperature. This climate based reduction in mean annual runoff was partially offset by a drought related decline in LAI that reduced the climate related reduction of mean annual runoff, effectively increased runoff, by 2–9%. Projected climate change may reduce mean annual runoff by between 6 and 31% in the study catchments. However, when LAI is allowed to respond to changes in climate the projected declines in runoff were reduced to between 2 and 22% in comparison to when the historical LAI was considered. Incorporating changes in LAI in VIC to respond to changing climate reduced the projected declines in streamflow and confirms the importance of including the effects of changes in vegetation productivity in future projections of streamflow.