Duncan, M.J.; Collins, D.B.G. Simple estimation of the effects of runoff on afforestation under different rainfall regimes
The hydrological effects of changing catchment vegetation cover are well known, and rainfall to runoff models have been used to predict those effects. However, use of these models may be constrained by data availability and expertise. There is thus a need for planners to have access to simple, science-based models that can be used confidently to indicate the degree of hydrological change caused by conversions between forest and grassland. Published relationships between rainfall parameters and flow changes accompanying afforestation of grassland or forest clearance have normally provided relationships with large uncertainties. In this study we critically examine the data from New Zealand paired catchment afforestation studies, details of the degree of forest cover, control catchment conditions, and catchment similarity. This process resulted in some studies being discarded, and allowed the adjustment of runoff from studies with partial forest cover to provide a data set for estimating runoff differences from fully forested catchments. The relationship compares well with an existing empirical model developed using a global dataset implying that this model may be more generally used across New Zealand as there are so few local studies. This suggests that both approaches may be useful for planning in New Zealand.