The impact of climate change and plantation development on streamflow in the Denmark River catchment, Western Australia

Abstract

The Denmark River is located in the southern coast of Western Australia and is an important water source for the Albany-Denmark Region, yielding up to 20 gigalitres (GL) per year. The river has had significant salinity issues due to clearing of native vegetation. The Quickup River dam was built in 1990 as an alternative water supply source for the town of Denmark; however in recent years it has not been able to supply enough water to meet demand. A target has been set to recover the Denmark River to potable water standards by 2020. Since 1990, commercial tree plantations have been established in the upper, high salt storage low-runoff, part of the catchment. Further plantings have been promoted as a means of reducing the salinity of the river. The Land Use Change Incorporated CATchment (LUCICAT), a distributed dynamic conceptual model, was used to assess the impact on streamflow and salinity due to climate and tree planting on future water yield. Three scenarios were modelled: (i) the historical sequence representing the 1975-2007 climate, (ii) recent climate representing the 1997-2007 climate, and (iii) future climate representing a 33-year climate series derived from different GCM projections of ∼2030 climate. Results showed that there would be about a 13% reduction in streamflow by 2030 due to tree planting in the upper part of the catchment under a continuation of the historical climate. If the recent climate continues there would be no significant change in streamflow as the average rainfall is similar to the 1975-2007 period. Under the future climate projections the projected reduction in streamflow would be 34%, ranging from 17% to 55% respectively due to a projected reduction in mean annual rainfall of 6.7% (range: 2.5% to 13%). However, projected streamflow reductions were even higher in the Yate Flat Creek catchment, where plantations were established in the late 1990s covering nearly all the cleared areas. The daily flow-duration of the catchment was about 77% during the historical period, and is projected to decrease to only 20-27% in future due to climate change and plantation development.