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A linked surface water-groundwater modelling approach to more realistically simulate rainfall-runoff non-stationarity in semi-arid regions

Deb, Proloy, Kiem, Anthony S., Willgoose, Garry
Journal of hydrology 2019
climatic factors, drought, groundwater, hydrologic models, runoff, semiarid zones, surface water, watersheds, Australia
Interactions between surface water (SW) and groundwater (GW) have been identified as a major contributing factor to non–stationarity in rainfall–runoff relationships. However, because existing rainfall–runoff models do not realistically account for these SW-GW interactions, they fail to robustly simulate runoff during multi-year droughts, especially in arid and semi-arid catchments that are relatively flat. Therefore, this study introduces a linked SW-GW modelling approach and tests it under different climatic conditions (Average, Dry and Wet periods) in two heterogeneous, semi-arid catchments in southeast Australia (SEA). The linked SW-GW modelling approach includes a fully-distributed SW (i.e. rainfall-runoff) model (SWATgrid) and a three-dimensional finite–difference GW model (MODFLOW). The results show that the linked SW-GW modelling approach produces highly improved runoff simulations for the study catchments, especially during dry conditions. These findings demonstrate the importance of accounting for SW-GW interactions when conducting rainfall-runoff modelling and highlights that failing to do so will result in overestimation of runoff during droughts – this is salient given projections for hotter and drier futures in many semi-arid regions. Although the study is focused on SEA, the insights gained are highly applicable for water managers in any region that experience high hydroclimatic variability or change.