Confirmation of <i>ACRU</i> model results for applications in land use and climate change studies

Abstract

The hydrological responses of a catchment are sensitive to, and strongly coupled to, land use and climate, and changes thereof. The hydrological responses to the impacts of changing land use and climate will be the result of complex interactions, where the change in one may moderate or exacerbate the effects of the other. A further difficulty in assessing these interactions will be that dominant drivers of the hydrological system may vary at different spatial and temporal scales. <br><br> To assess these interactions, a process-based hydrological model, sensitive to land use and climate, and changes thereof needs to be used. For this purpose the daily time step <i>ACRU</i> model was selected. However, to be able to use a hydrological model such as <i>ACRU</i> with confidence its representation of reality must be confirmed by comparing simulated output against observations across a range of climatic conditions. Comparison of simulated against observed streamflow was undertaken in three climatically diverse South African catchments, ranging from the semi-arid sub-tropical Luvuvhu catchment, to the winter rainfall Upper Breede catchment and the sub-humid Mgeni catchment. Not only do the climates of the catchments differ, but their primary land uses also vary. In the upper areas of the Mgeni catchment commercial plantation forestry is dominant, while in the middle reaches there are significant areas of commercial plantation sugarcane and urban areas, while the lower reaches are dominated by urban areas. The Luvuvhu catchment has a large proportion of subsistence agriculture and informal residential areas. In the Upper Breede catchment in the Western Cape, commercial orchards and vineyards are the primary land uses. <br><br> Overall the <i>ACRU</i> model was able to represent the high, low and total flows, with satisfactory Nash-Sutcliffe efficiency indexes obtained for the selected catchments. The study concluded that the <i>ACRU</i> model could be used with confidence to simulate the streamflows of the three selected catchments and was able to represent the hydrological responses from the range of climates and diversity of land uses present within the catchments

Climate change impacts and adaptation in South Africa

“…South African researchers have studied the biophysical impacts of climate change, assessing, for example, the combined impacts of climate change and other drivers on biodiversity, and applying these insights to spatial-planning processes and the optimizing of conservation responses 39,102,104,130 and water management. [66][67][68]131,132 Initiatives under the SA Global Change Programme have injected new momentum into research, training and monitoring for earth system science that should enhance South Africa's existing capacity. The LTAS sectoral assessments are helping to identifying key knowledge gaps and priorities for new research.…”

“…29,[64][65][66] The hydrological system is dynamic, and changes in climate may result in unanticipated hydrological responses, possibly beyond the ranges for which the models' ability to represent processes has been tested. 67 Preliminary projections under the wide range of scenarios generated by the MIT hybrid approach (see LTAS side bar) for runoff range from a 20% decrease to a 60% increase by as early as 2050 under an unmitigated emissions pathway, while under a constrained emissions scenario projections of runoff range from a 5% decrease to a 20% increase. It is worth noting that a 60% increase in rainfall is a low probability outcome from the modeling framework, and is also physically very implausible.…”

Assessing Impacts of Land Use Changes on the Hydrology of a Lowland Rainforest Catchment in Ghana, West Africa

“…The ACRU model has previously been applied in the catchment with a Nash-Sutcliffe efficiency (NSE) index of 0.6 and 0.5, and R 2 of 0.8 and 0.7, for calibration and validation of monthly flows, respectively [37]. This study builds on this application, as well as knowledge gained through several applications of the model in a variety of catchments [13,43,44], with a wide range of climates and land uses. …”

“…The impacts of land cover/land use changes on hydrology have been assessed over the past several decades, using (i) field-based data-driven statistical methods, based on single catchments or paired catchments [6,7] and (ii) hydrological modelling [8][9][10][11][12][13]. Hydrological modelling using physically based tools are reported to provide reasonable representation of observed hydrological processes for large areas, and also enable rapid evaluation of catchment development scenarios [14], using relatively less time and resources than field studies.…”

Multi-variable verification of hydrological processes in the upper North Saskatchewan River basin, Alberta, Canada

“…Schulze 1982, Schulze and George 1987, Smithers and Caldecott 1993, Kienzle et al 1997, Jewitt et al 1999, Kienzle and Schmidt 2008, Forbes et al 2011); (c) has undergone rigorous sensitivity analyses (Schulze 1995, Kienzle 2010; and (d) is sensitive to perturbations in the drivers of the hydrological processes (changes in temperature, precipitation, and CO 2 ) and their feedbacks on transpiration and evaporative demand (Warburton et al 2010).…”