Physically-based modeling of topographic effects on spatial evapotranspiration and soil moisture patterns through radiation and wind

Abstract

<jats:p>Abstract. In this paper, simulations with the Soil Water Atmosphere Plant (SWAP) model are performed to quantify the spatial variability of both potential and actual evapotranspiration (ET), and soil moisture content (SMC) caused by topography-induced spatial wind and radiation differences. To obtain the spatially distributed ET/SMC patterns, the field scale SWAP model is applied in a distributed way for both pointwise and catchment wide simulations. An adapted radiation model from r.sun and the physically-based meso-scale wind model METRAS PC are applied to obtain the spatial radiation and wind patterns respectively, which show significant spatial variation and correlation with aspect and elevation respectively. Such topographic dependences and spatial variations further propagate to ET/SMC. A strong spatial, seasonal-dependent, scale-relevant intra-catchment variability in daily/annual ET and less variability in SMC can be observed from the numerical experiments. The study concludes that topography has a significant effect on ET/SMC in the humid region where ET is a energy limited rather than water availability limited process. It affects the spatial runoff generation through spatial radiation and wind, therefore should be applied to inform hydrological model development. In addition, the methodology used in the study can serve as a general method for physically-based ET estimation for data sparse regions.</jats:p>

Using expert knowledge to increase realism in environmental system models can dramatically reduce the need for calibration

“…In absence of significant topographic gradients and due to the potentially increased unsaturated storage capacity, it can be hypothesized that the primary functions of plateaus are sub-surface storage and groundwater recharge (Savenije, 2010). Although plateaus may experience infiltration excess overland flow in specific locations, the topographical gradients may not be sufficient to generate surface runoff connected to the stream network (Liu et al, 2012). In the FLEX-TOPO approach the proportions of the hydrologically distinct landscape units, i.e., HRUs, in a given catchment need to be determined on the basis of topographical and land cover information.…”

“…These strategies included the attempt to incorporate different data sources in the parameter estimation process, such as ground-and soil water dynamics (e.g., Seibert and McDonnell, 2002;Freer et al, 2004;Fenicia et al, 2008a;Matgen et al, 2012;Sutanudjaja et al, 2013), remotely sensed evaporation (e.g., Winsemius et al, 2008), snow dynamics (e.g., Parajka and Blöschl, 2008) or tracer data (e.g., Vaché and McDonnell, 2006;Dunn et al, 2008;Son and Sivapalan, 2007;Birkel et al, 2011;Capell et al, 2012;Hrachowitz et al, 2013a). Alternatively, one may seek to extract more information from available data, for example through the development of signatures representing different aspects of the data (e.g., Gupta et al, 1998Gupta et al, , 2008Boyle et al, 2000Boyle et al, , 2001Madsen, 2000;Fenicia et al, 2006;Rouhani et al, 2007;Khu et al, 2008;Winsemius et al, 2009;Bulygina and Gupta, 2010;McMillan et al, 2011;Clark et al, 2011;Euser et al, 2013;He et al, 2014;Hrachowitz et al, 2014).…”

Simulation of Actual Evapotranspiration and Evaluation of Three Complementary Relationships in the Upper Regions of the Mekong River and the Salween River

“…Precipitation affects ET a through soil moisture constraints, especially in arid regions. For example, with high precipitation, ET a is less limited to soil moisture, and the ET a might be the same as the potential evapotranspiration (Liu et al 2012). However, in arid environments with limited precipitation, the soil water content is insufficient, and ET a tends to be largely dependent on available soil water.…”

Gravitational and capillary soil moisture dynamics for distributed hydrologic models

“…The state dynamics are affected by hydrometeorological forcing of precipitation, radiation, and atmospheric evaporative demand. Furthermore, topography, land use, and soil properties across the landscape, affect soil moisture temporal evolution (Western and Grayson, 2000;Lawrence and Hornberger, 2007;Vereecken et al, 2007;Ivanov et al, 2010;Liu et al, 2012;Beven and Germann, 2013).…”