Authors: Greaser, K; Weinig, W

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Greaser, K & Weinig, W 2022, 'The importance of climate for evapotranspiration cover design', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1139-1152,

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Mine closure typically includes covering various waste facilities to stabilise landforms, control seepage, reduce erosion, and protect the environment. Commonly, evapotranspiration covers (also referred to as alternative, store and release, or water balance covers) are preferred for many mine sites. Evapotranspiration (ET) covers rely on evaporation and transpiration to reduce seepage through mine waste, which may require management or treatment to avoid adverse environmental impacts. Given ET covers rely on the natural processes of evaporation and transpiration to reduce seepage, the surrounding climate will ultimately control the performance of the ET cover. Consequently, climate is a key factor in predicting the performance of an ET cover. Several guidance documents have been published regarding best practices for the design of ET covers, although current guidance does not include comprehensive, detailed standards or best practices to develop a climate set to be used in soil-atmosphere modelling to design ET covers. This paper presents important factors to consider when compiling a climate set for soil-atmosphere modelling to design an ET cover, beyond the generalisations in current guidance documents, so that designers can make informed decisions when developing a representative climate set. Ideally, a climate set for soil-atmosphere modelling to support ET cover design would be developed using 100year dataset, including co-located, daily measured precipitation and estimated potential evapotranspiration (PET). Using a shorter climate set presents the risk of over- or underestimating net infiltration. Accurate simulation of the variation of both precipitation and PET at several time scales is critical for ET cover design. This includes the distribution of precipitation and PET throughout the year as well as variations over the long-term. Representing the distribution of precipitation seasonally (e.g. between winter and summer or dry and wet seasons), the number of days of precipitation in a year, the intensity of precipitation, and the frequency of storm cycles are important considerations. The relationship between precipitation and PET is critical to understand and simulate appropriately. Because relationships between precipitation and temperature, relative humidity, wind speed, and solar radiation are complex, combining data measured at multiple sites may not represent climate at any one site appropriately. When compiling climate sets, significant preference should be given to scaling climate data from one location rather than combining data from multiple locations. Further, although many climate models have been developed, users should be aware of the basis of formulation for each model, the errors in the models, the quality of the data used to develop the model, and comparisons of the modelled data to measured data for the mine site to adjust the modelled data appropriately. Finally, developing a robust climate set with uncertainty limited to a practical extent will also serve to reduce uncertainty in predicting the potential influence of climate change.

Keywords: evapotranspiration cover design, water balance cover design, soil-atmosphere modelling, climate for soil-atmosphere modelling

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