Responses of evapotranspiration at different topographic positions and catchment water balance following a pronounced drought in a mixed species eucalypt forest, Australia
Patrick J. Mitchell, Richard G. Benyon, Patrick N.J. Lane
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引用次数: 60
Abstract
Across southern Australia, a large proportion of urban water supply is sourced from mountainous catchments forested with native eucalypts. Mixed species eucalypt forest (MSEF) is the most common forest type in this region and occurs on relatively dry, fire prone sites, yet factors controlling forest water use and stream flow in response to topography, disturbance and drought are poorly understood. This study investigated the patterns and drivers of water balance over a 4 year period in a 1.36 km2, MSEF catchment by: quantifying spatial and temporal variability in evapotranspiration (Et) and its components; evaluating the abiotic, structural and physiological factors controlling water use across the catchment; and testing the effects of antecedent soil water conditions on water fluxes after drought. This was done using a ‘bottom up’ measurement approach that included stream flow and Et (sap flow, interception troughs and evaporation dome) and a simple empirical model of Et to track catchment response to drought. Spatial variability was considerable, with 40% lower rates of Et at an up slope plot compared to mid and bottom slope plots. Tree transpiration was the dominant flux annually and was correlated to reference Et (r2 = 0.35–0.80), implying strong limitation by atmospheric demand across the catchment. Annual Et totals were relatively consistent between years (841 ± 34 mm) despite large variation in rainfall (463–1179 mm y−1). Annual stream flow represented a very small proportion of the water budget (<2% of rainfall) and showed little recovery from the drought period. The modelling showed that the change in soil water storage following drought was large (up to −330 mm) and was responsible for decreased rates of stream flow. These findings show that Et in the MSEF is sensitive to topography and demand limitation and suggests that water yield in this forest type may be particularly sensitive to future climatic change as shown by the sustained effect of drought on catchment water balance.
在澳大利亚南部,城市供水的很大一部分来自种植着当地桉树的山区集水区。混合种桉树林(MSEF)是该地区最常见的森林类型,生长在相对干燥、易发火灾的地点,但对地形、干扰和干旱对森林水利用和溪流流量的控制因素了解甚少。本研究通过量化蒸散发(Et)及其组分的时空变化,探讨了1.36 km2 MSEF流域4年水平衡的模式和驱动因素;评价控制流域用水的非生物、结构和生理因素;试验了前期土壤水分条件对干旱后水通量的影响。这是使用“自下而上”的测量方法完成的,该方法包括溪流流量和Et(液流、截流槽和蒸发穹顶),以及一个简单的Et经验模型来跟踪流域对干旱的响应。空间变异性相当大,与中坡和底坡样地相比,上坡样地的Et速率低40%。树木蒸腾是主要的年通量,并与参考Et相关(r2 = 0.35-0.80),表明整个流域受大气需求的强烈限制。年Et总量在年之间相对一致(841±34 mm),尽管降雨量变化较大(463-1179 mm y−1)。年流量在水收支中所占的比例很小(占降雨量的2%),并且在干旱期几乎没有恢复。该模型表明,干旱后土壤储水量的变化很大(高达- 330毫米),这是导致水流速率下降的原因。这些发现表明,MSEF中的Et对地形和需求限制敏感,并表明该森林类型的水量可能对未来气候变化特别敏感,如干旱对流域水平衡的持续影响所示。
期刊介绍:
The Journal of Hydrology publishes original research papers and comprehensive reviews in all the subfields of the hydrological sciences including water based management and policy issues that impact on economics and society. These comprise, but are not limited to the physical, chemical, biogeochemical, stochastic and systems aspects of surface and groundwater hydrology, hydrometeorology and hydrogeology. Relevant topics incorporating the insights and methodologies of disciplines such as climatology, water resource systems, hydraulics, agrohydrology, geomorphology, soil science, instrumentation and remote sensing, civil and environmental engineering are included. Social science perspectives on hydrological problems such as resource and ecological economics, environmental sociology, psychology and behavioural science, management and policy analysis are also invited. Multi-and interdisciplinary analyses of hydrological problems are within scope. The science published in the Journal of Hydrology is relevant to catchment scales rather than exclusively to a local scale or site.