11Wetlands are conservation priorities worldwide, due to their high biodiversity and productivity, but are 12 under threat from agricultural and climate change stresses. To improve the water management practices 13 and resource allocation in these complex systems, a modelling approach has been developed to estimate 14 potential recharge for data poor catchments using rainfall data and basic assumptions regarding soil and 15 aquifer properties. The Verlorenvlei estuarine lake (RAMSAR #525) on the west coast of South Africa 16 is a data poor catchment where rainfall records have been supplemented with farmer's rainfall records. 17The catchment has multiple competing users. To determine the ecological reserve for the wetlands, the 18 spatial and temporal distribution of recharge had to be well constrained using the J2000 rainfall/runoff 19 model. The majority of rainfall occurs in the mountains (±650 mm/yr) and considerably less in the 20 valley (±280 mm/yr). Percolation was modelled as ~3.6% of rainfall in the driest parts of the catchment, 21 ~10% of rainfall in the moderately wet parts of the catchment and ~8.4% but up to 28.9% of rainfall in 22 the wettest parts of the catchment. The model results are representative of rainfall and water level 23 measurements in the catchment, and compare well with water table fluctuation technique, although 24 30 31 4 groundwater level. This approach can also be called actual recharge, as it determines the amount of 59 water that reaches the groundwater table (Rushton, 1997), but in doing so it neglects any processes that 60 occur in the unsaturated zone, thereby reducing its spatial and temporal extent. However, for numerical 61 modelling of recharge, it is not possible to neglect what is happening in the unsaturated zone, as most 62 models require information on the physical and chemical pathways of recharge. Therefore, this type of 63 approach is rather defined as potential recharge, which is constrained by the amount of water that has 64 percolated through the unsaturated zone, contributing to the saturated zone (Rushton, 1997), and hence 65 requires knowledge of the percolation rate. 66Within numerical modelling, the percolation rate (Scanlon et al., 2002) can be modelled either by 67 looking at variably saturated flow or rainfall/runoff partitioning. Both these methods use a water-68 balance to determine the percolation volume using input data, such as climate (rainfall, temperature), 69 vegetation (interception) and biosphere (soil texture) to partition water into runoff, infiltration, 70 evaporation and recharge. These two methods differ in their ability to simulate soil moisture. Variably 71 saturated flow models can simulate vertical distributions of soil moisture and estimate recharge by 72 routing water through the soil column using soil hydraulic conductivities. Many rainfall/runoff models 73 partition infiltrated water into storages based on soil type parameters (J2000: Krause, 2001; and ACRU: 74 Schulze, 1995) . This makes variably saturated flow more favoura...

Abstract. River systems that support high biodiversity profiles are conservation priorities worldwide. Understanding river ecosystem thresholds to low-flow conditions is important for the conservation of these systems. While climatic variations are likely to impact the streamflow variability of many river courses into the future, understanding specific river flow dynamics with regard to streamflow variability and aquifer baseflow contributions is central to the implementation of protection strategies. While streamflow is a measurable quantity, baseflow has to be estimated or calculated through the incorporation of hydrogeological variables. In this study, the groundwater components within the J2000 rainfall–runoff model were distributed to provide daily baseflow and streamflow estimates needed for reserve determination. The modelling approach was applied to the RAMSAR-listed Verlorenvlei estuarine lake system on the west coast of South Africa, which is under threat due to agricultural expansion and climatic fluctuations. The sub-catchment consists of four main tributaries, Krom Antonies, Hol, Bergvallei and Kruismans. Of these, Krom Antonies was initially presumed the largest baseflow contributor, but was shown to have significant streamflow variability attributed to the highly conductive nature of the Table Mountain Group sandstones and Quaternary sediments. Instead, Bergvallei was identified as the major contributor of baseflow. Hol was the least susceptible to streamflow fluctuations due to the higher baseflow proportion (56 %) as well as the dominance of less conductive Malmesbury shales that underlie it. The estimated flow exceedance probabilities indicated that during the 2008–2017 wet cycle average lake inflows exceeded the average evaporation demand, although yearly rainfall is twice as variable in comparison to the first wet cycle between 1987 and 1996. During the 1997–2007 dry cycle, average lake inflows are exceeded 85 % of the time by the evaporation demand. The exceedance probabilities estimated here suggest that inflows from the four main tributaries are not enough to support Verlorenvlei, with the evaporation demand of the entire lake being met only 35 % of the time. This highlights the importance of low-occurrence events for filling up Verlorenvlei, allowing for regeneration of lake-supported ecosystems. As climate change drives increased temperatures and rainfall variability, the length of dry cycles is likely to increase into the future and result in the lake drying up more frequently. For this reason, it is important to ensure that water resources are not over-allocated during wet cycles, hindering ecosystem regeneration and prolonging the length of these dry cycle conditions.

Semi-arid catchments under change: Adapted hydrological models to simulate the influence of climate change and human activities on rainfall-runoff processes in southern Africa. In: Climate change and adaptive land management in southern Africa -assessments, changes, challenges, and solutions (ed. by Water resources 114C A Abstract: A comprehensive river basin assessment is key to integrated land and water resources management (ILWRM), which is based on an integrated system analysis to identify interacting hydrological processes that are driven by landscape features and socioeconomic development. Software toolsets like RBIS (River Basin Information System), GRASS-HRU, and the hydrological modelling system JAMS/J2000 were used and further developed for basin assessments and modelling of hydrological process dynamics and other environmental processes in selected catchments in southern Africa. These are the Gaborone Dam catchment (Botswana, South Africa), the Verlorenvlei catchment (South Africa), and the Luanginga catchment (Angola, Zambia). All of these catchments respond very sensitively to changes in climate and land management, revealing additional issues like a strong decline of infl ow (Gaborone Dam) or a decline of usable groundwater resources (Verlorenvlei). Further, extensive wetland areas in the Upper Zambezi (Luanginga) respond strongly to changes in hydroclimatic conditions and land management. In this study, newly developed and improved simulation components for representing processes with a strong local impact on the hydrological conditions such as fl oodplain inundation, irrigation, small farm dams, and contour bank farming were used to more precisely simulate the hydrology of the respective basins. After successful model validation and an improved understanding of catchment dynamics, the models were used as a platform for diff erent land or climate change analysis. Taking the RCP 8.5 scenario based on EC-Earth and ECHAM, downscaled by REMO, into account, the Luanginga catchment showed a strong decrease in runoff generation, inundation extent, and groundwater recharge. For the Kruismannsrivier, a sub-catchment of the Verlorenvlei, the relation between contour farming and related eff ects on surface/subsurface runoff processes and related parameters were revealed through modelling. These fi ndings could also be projected to the Gaborone Dam catchment, in which the infl uence of small farm dams spread over the catchment could be shown by modelling.Resumo: Uma avaliação abrangente da bacia hidrográfi ca é essencial para a gestão integrada dos recursos terrestres e hí-dricos (ILWRM), a qual é baseada numa análise integrada do sistema para identifi car processos hidrológicos em interacção que são impulsionados pelas características da paisagem e o desenvolvimento socioeconómico. Ferramentas de software, tais como RBIS (River Basin Information System), GRASS-HRU e o sistema de modelação hidrológica JAMS/J2000,foram utilizadas e desenvolvidas para avaliações de bacias e modelação de dinâmicas de processo...

Climate change and adaptive land management in southern Africa -assessments, changes, challenges, and solutions. Biodiversity & Ecology, 6, Klaus Hess Publishers, Göttingen & Windhoek.

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