Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 11 2 2007 10.5194/hess-11-965-2007 http://www.hydrol-earth-syst-sci.net/11/965/2007/ http://www.hydrol-earth-syst-sci.net/11/965/2007/hess-11-965-2007.html http://www.hydrol-earth-syst-sci.net/11/965/2007/hess-11-965-2007.pdf 965 982 2007-03-05 Sensitivity of point scale surface runoff predictions to rainfall resolution A. J. Hearman C. Hinz christoph.hinz@uwa.edu.au School of Earth and Geographical Sciences, The University of Western Australia, Crawley, Australia This paper investigates the effects of using non-linear, high resolution rainfall, compared to time averaged rainfall on the triggering of hydrologic thresholds and therefore model predictions of infiltration excess and saturation excess runoff at the point scale. The bounded random cascade model, parameterized to three locations in Western Australia, was used to scale rainfall intensities at various time resolutions ranging from 1.875 min to 2 h. A one dimensional, conceptual rainfall partitioning model was used that instantaneously partitioned water into infiltration excess, infiltration, storage, deep drainage, saturation excess and surface runoff, where the fluxes into and out of the soil store were controlled by thresholds. The results of the numerical modelling were scaled by relating soil infiltration properties to soil draining properties, and in turn, relating these to average storm intensities. For all soil types, we related maximum infiltration capacities to average storm intensities (k*) and were able to show where model predictions of infiltration excess were most sensitive to rainfall resolution (ln k*=0.4) and where using time averaged rainfall data can lead to an under prediction of infiltration excess and an over prediction of the amount of water entering the soil (ln k*>2) for all three rainfall locations tested. For soils susceptible to both infiltration excess and saturation excess, total runoff sensitivity was scaled by relating drainage coefficients to average storm intensities (g*) and parameter ranges where predicted runoff was dominated by infiltration excess or saturation excess depending on the resolution of rainfall data were determined (ln g*<2). Infiltration excess predicted from high resolution rainfall was short and intense, whereas saturation excess produced from low resolution rainfall was more constant and less intense. This has important implications for the accuracy of current hydrological models that use time averaged rainfall under these soil and rainfall conditions and predictions of larger scale phenomena such as hillslope runoff and runon. It offers insight into how rainfall resolution can affect predicted amounts of water entering the soil and thus soil water storage and drainage, possibly changing our understanding of the ecological functioning of the system or predictions of agri-chemical leaching. The application of this sensitivity analysis to different rainfall regions in Western Australia showed that locations in the tropics with higher intensity rainfalls are more likely to have differences in infiltration excess predictions with different rainfall resolutions and that a general understanding of the prevailing rainfall conditions and the soil's infiltration capacity can help in deciding whether high rainfall resolutions (below 1 h) are required for accurate surface runoff predictions. Beven, K.: Runoff generation in semi-arid areas, Chapter 3, in: Dryland Rivers, Hydrology and geomorphology of semi-arid channels, edited by: Bull, L. J. and Kirkby, M. J., John Wiley and Sons Ltd, Sussex, England, 2002. Brooks, R. H. and Corey, A. T.: Hydraulic properties of porous media, Hydrology Paper 3, Colorado State University, Fort Collins, CO, 27110, 1964. Bronstert, A. and Bardossy, A.: Uncertainty of runoff modelling at the hillslope scale due to temporal variations of rainfall intensity, Phys. Chem. Earth, 28, 283–288, 2003. Cammeraat, E. L. H.: Scale dependent thresholds in hydrological and erosion response of a semi-arid catchment in southeast Spain, Agric., Ecosyst. Environ., 104, 317–332, 2004. Farmer, D., Sivapalan, M., and Jothityangkoon, C.: Climate, soil and vegetation controls upon the variability of water balance in temperate and semiarid landscapes: Downward approach to water balance analysis, Water Resour. Res., 39(2), 1035–1055, 2003. Harris, D., Menabde, M., Seed, A., and Austin, G.: Breakdown coefficients and scaling properties of rain fields, Nonlin. Processes Geophys., 5, 93–104, 1998. Hipsey, M. R., Sivapalan, M., and Menabde, M.: A risk-based approach to the design of rural water supply catchments across Western Australia, Hydrol. Sci., 48(5), 709–727, 2003. Horton, R. E.: The role of infiltration in the hydrological cycle, Transact. Amer. Geophys. Union, 14, 446–460, 1933. Kirkby, M. J., Bracken, L. J., and Shannon, J.: The influence of rainfall distribution and morphological factors on runoff delivery from dryland catchments in SE Spain, Catena, 62, 136–156, 2005. Kirkby, M. J. and Cox, N. J.: A climatic index for soil erosion potential (CSEP) including seasonal and vegetation factors, Catena, 25, 333–352, 1995. Lovejoy, S. and Schertzer, D.: Multifractals, cloud radiances and rain, J. Hydrol., 322, 59–88, 2005. Menabde, M. and Sivapalan, M.: Modeling of rainfall time series and extremes using bounded random cascades and Levy-stable distributions, Water Resour. Res., 36(11), 3293–3300, 2000. Menabde, M., Harris, D., Seed, A., Austin, G., and Stow, D.: Multiscaling properties of rainfall and bounded random cascades, Water Resour. Res., 33(12), 2823–2830, 1997. Mertens, J., Raes, D., and Feyen, J.: Incorporating rainfall intensity into daily rainfall records for simulating runoff and infiltration into soil profiles, Hydrol. Processes, 16, 731–739, 2002. Milly, P. C. D.: Climate, interseasonal storage of soil water and the annual water balance, Adv. Water Resour., 17, 19–24, 1994. Over, T. M. and Gupta, V. K.: A space-time theory of mesoscale rainfall using random cascades, J. Geophys. Res., 101, 26 319–26 331, 1996. Potter, N. J., Zhang, L., Milly, P. C. D., McMahon, T. A., and Jakeman, A. J.: Effects of rainfall seasonality on soil moisture capacity on mean annual water balance for Australian catchments, Water Resour. Res., 41, W06007, doi:10.1029/2004WR003697, 2005. Puigdefabregas, J., Sole, A., Barrio, G., and Boer, M.: Scales and processes of water and sediment redistribution in drylands: Results from the Rambla Honda field site in Southeast Spain, Earth Sci. Rev., 48, 39–70, 1999. Rawls, W. J., Ahuga, L. R., and Brakensiek, D. L.: Estimating soil hydraulic properties from soils data, in: Indirect Methods for Estimating the Hydraulic Properties of Unsaturated Soils, edited by: van Genuchten, M. T., Leij, F. J., and Lund, L. J., University of California, Riverside, California, pp 329–340, 1992. Reaney, S. M., Bracken, L. J., and Kirkby, M. J.: Use of the conncectivity of runoff model (CRUM) to investigate the influence of storm characteristics on runoff generation and connectivity in semi-arid areas, Hydrol. Processes, [online] doi:10.1002/hyp.6281, 2007. Singh, V. P.: Effect of spatial and temporal variability in rainfall and watershed characteristics on stream flow hydrographs, Hydrol. Processes, 11, 1649–1669, 1997. Stomph, T. J., de Ridder, N., Steenhuis, T. S., and van de Giesen, N. C.: Scale effects of Hortonian overland flow and rainfall-runoff dynamics: Laboratory validation of a process-based model, Earth Surface Processes and Landforms, 27, 847–855, 2002. Struthers, I., Sivapalan, M., and Hinz, C.: A multiple wetting front gravitational infiltration and redistribution model for water balance applications, Water Resour. Res., 42(6), W06406, doi:10.1029/2005WR004645, 2006. Struthers, I., Sivapalan, M., and Hinz, C.: Conceptual examination of climate-soil controls upon rainfall partitioning in an open-fractured soil I: Single storm response, Adv. Water Resour., 30, 505–517, 2007a. Struthers, I., Hinz, C., and Sivapalan, M.: Conceptual examination of climate-soil controls upon rainfall partitioning in an open-fractured soil II: Response to a population of storms, Adv. Water Resour., 30, 518–527, 2007b. Wainwright, J. and Parsons, A. J.: The effect of temporal variations in rainfall on scale dependency in runoff coefficients, Water Resour. Res., 38(12), 1271–1281, 2002. Wolfram Research Inc.: Mathematica, Version 5.2, Champaign, Illinois, 2005. Woods, R.: The relative roles of climate, soil, vegetation and topography in determining seasonal and long-term catchment dynamics, Adv. Water Resour., 26, 295–309, 2003. Woolhiser, D. A. and Goodrich, D. C.: Effect of storm rainfall intensity patterns on surface runoff, J. Hydrol., 102, 335–354, 1988. Veneziano, D., Bras, R. L., and Nuiemann, J. D.: Nonlinearity and self-similarity of rainfall in time and a stochastic model, J. Geophys. Res., 101, 26 371–26 392, 1996. Yu, B.: A comparison of the Green-Ampt and a spatially variable infiltration model for natural storm events, Transact. ASAE, 42(2), 89–97, 1999. Yu, B., Rose, C. W., Coughlan, K. J., and Fentie, B.: Plot-scale rainfall-runoff characteristics and modelling at six sites in Australia and southeast Asia, Transact. ASAE, 40(5), 1295–1303, 1997.