Modelling the effect of land management interventions and climate change on sediment loads in the Manawatū-Whanganui region

SedNetNZ is used to model the effect of erosion control undertaken under the Sustainable Land Use Initiative (SLUI) and predict the effect of climate change on sediment load in the Manawatū-Whanganui region. Sediment load in 2004 is estimated at 13.4 Mt yr −1 ; by 2018, ≈5000 km 2 of land had farm plans implemented and annual sediment load reduced by 6.2% of the 2004 load. If SLUI stops at the 2018 level of implementation, by 2038 it is predicted to achieve a 15.7% reduction in annual sediment load. If SLUI continues to implement farm plans, 7949 km 2 of land will be treated by 2043 and annual sediment load could be reduced by a further 14.7%. Climate change is predicted to substantially increase sediment loads. By 2043 annual sediment load for the region is predicted to increase, compared to 2004, by between 8.3 and 23.7%. However, this can largely be offset by SLUI works. By 2090 an annual sediment load increase of between 53 and 224% due to climate change is predicted. The results suggest climate warming may dominate changes in sediment load in the future.