The role of interannual rainfall variability on runoff generation in a small dry sub-humid watershed with disperse tree cover

Susanne Schnabel, Alvaro Gómez-Gutiérrez


Recent studies in small experimental catchments under Mediterranean-type climate revealed a complex hydrological catchment response, presenting saturation excess runoff generation and, to a minor degree, infiltration excess flow. Many of these catchments, however, belong to areas with sub-humid or humid Mediterranean climate. Catchment studies were carried out since 1991 in savannah-like grazed land (dehesas), which are widespread in south-western Spain, and also elsewhere in the Mediterranean. Albeit knowledge gained by previous studies, no thorough analysis has been carried out on the temporal variation of discharge production using the complete dataset. The objectives include i) an analysis of the temporal variation of discharge and rainfall at different temporal scales, ii) exploration of the role of antecedent soil moisture conditions in runoff production, iii) empirical modeling of rainfallrunoff relationships at the event scale and iv) definition of the importance of interannual rainfall variation on discharge production. The analysis were based on rainfall and runoff which were monitored at a time resolution of 5 minutes and periodically measured soil moisture from various depth in the valley bottom. Regression analysis as well as the comparison of hydrographs illustrate on the importance of antecedent rainfall conditions. Soil moisture in the valley bottom was crucial to understand the hydrological behaviour of the catchment. A soil moisture threshold of 0.37 m3 m-3 was defined above which runoff coefficients increase sharply. This situation is reached with 170 mm of antecedent rain falling in a continuous way. The results indicate that saturation excess flow and preferential subsurface flow processes are responsible of most of the runoff generated. Hortonian type overland flow dominates under dry soil conditions and is produced by high intensity rainfall. Non-linear regression analysis with data grouped according to antecedent catchment conditions produced highly significant regression models, explaining event discharge with three variables: Maximum 60-minute rainfall intensity (I60), event rainfall minus I60 and mean antecedent daily rainfall. Variability of monthly runoff is best explained by interannual rainfall variation rather than by mean seasonal distribution. During droughts, which are a common feature in the Mediterranean, discharge was very low. Runoff is highly concentrated in time with 10% of the months accounting for 85% of total discharge.


discharge, rainfall, soil moisture, empirical modelling, drought, dehesa,

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Beven, K. 2002. Runoff generation in semi-arid areas. In Dryland Rivers: Hydrology and Geomorphology of Semi-Arid Channels, L.J. Bull, M.J. Kirkby (eds.), John Wiley and Sons, New York, pp. 57-105.

Bos, M.G., Replogle, J.A., Clemmens, A.J. 1986. Aforadores de caudal para canales abiertos. Vol. 38. International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands.

Castillo, V.M., Gómez-Plaza, A., Martínez-Mena, M. 2003. The role of antecedent soil water content in the runoff response of semiarid catchments: a simulation approach. Journal of Hydrology 284, 114-130.

Ceballos A., Schnabel, S. 1998. Hydrological behaviour of a small catchment in the Dehesa landuse system (Extremadura, SW Spain). Journal of Hydrology 210, 146-160.

Dahlgren, R.A., Tate, K.W., Lewis, D.J., Atwill, E.R., Harper, J.M., Allen-Diaz, B.H. 2001. Watershed research examines rangeland management effects on water quality. Californian Agriculture 55, 64-71.

Dirksen, C. 1999. Soil Physics Measurements. Catena Verlag, Reiskirchen, 154 pp.

Gallart, F., Llorens, P., Latron, J., Regüés, D. 2002. Hydrological processes and their seasonal controls in a small Mediterranean mountain catchment in the Pyrenees. Hydrology and Earth System Sciences 6, 527-537.

Gallart, F., Latron, J. Llorens, P. 2005. Catchment dynamics in a Mediterranean mountain environment. The Vallcebre research basins (South Eastern Pyrenees) I: Hydrology. Developments in Earth Surface Processes 7, 1-16.

Gallart, F., Amaxidis, Y., Botti, P., Canê, G., Castillo, V., Chapman, P., Froebrich, J., García- Pintado, J., Latron, J., Llorens, P., Lo Porto, A., Morais, M., Neves, R., Ninov, P., Perrin, J.L., Ribarova, I., Skoulikidis, N., Tournoud, M.G. 2008. Investigating hydrological regimes and processes in a set of catchments with temporary waters in Mediterranean Europe. Hydrological Sciences Journal 53, 618-628.

García-Ruiz, J.M., Arnáez, J., Beguería, S., Seeger, M., Martí, C., Regüés, D., Lana-Renault, N., White, S. 2005. Flood generation in an intensively disturbed, abandoned farmland catchment, Central Spanish Pyrenees. Catena 59, 79-92.

García-Ruiz, J.M., Regüés, D., Alvera, B., Lana-Renault, N., Serrano-Muela, P., Nadal-Romero, E., Navas, A., Latron, J., Martí-Bono, C. 2008. Flood generation and sediment transport in experimental catchments along a plant cover gradient in the Central Pyrenees. Journal of Hydrology 356, 245-260.

Gómez Amelia, D. 1985. La penillanura cacereña. Estudio geomorfológico. Universidad de Extremadura, Cáceres.

Lana-Renault, N., Latron, J., Regüés, D. 2007. Streamflow response and water-table dynamics in a sub-Mediterranean research catchment (Central Pyrenees). Journal of Hydrology 347, 497-507.

Latron, J., Gallart, F. 2008. Runoff generation processes in a small Mediterranean research catchment (Vallcebre, Eastern Pyrenees). Journal of Hydrology 358, 206-220.

Latron, J., Soler, M., Llorens, P., Gallart. F. 2008. Spatial and temporal variability of the hydrological response in a small Mediterranean research catchment (Vallcebre, Eastern Pyrenees). Hydrological Processes 22, 775-787.

Lewis, D., Singer, M.J., Dahlgren R.A., Tate, K.W. 2000. Hydrology in a California oak woodland watershed: A 17-year study. Journal of Hydrology 240, 106-117.

Maneta, M. 2006. Modeling of the hydrologic processes in a small semiarid catchment. Unpublished PhD Thesis, Universidad de Extremadura, Cáceres, 310 pp.

Maneta M.P., Schnabel, S., Jetten V.G. 2007. Continuous spatially distributed simulation of surface and subsurface hydrological processes in a small semi-arid catchment. Hydrological Processes 21, 2196-2214.

Maneta, M., Pasternack, G.B., Wallender, W.W., Jetten, V.D., Schnabel, S. 2007. Temporal instability of parameters in an event-based distributed hydrologic model applied to a small semi-arid catchment. Journal of Hydrology 341, 207-221.

Maneta, M., Schnabel, S., Wallender, W., Panday, S., Jetten, V. 2008. Calibration of an evapotranspiration model to simulate soil water dynamics in a semiarid rangeland. Hydrological Processes 22, 4655-4669.

Moré, J.J. 1977. The Levenberg-Marquardt Algorithm: Implementation and Theory. In Lecture Notes in Mathematics, G.A. Watson (ed.), Springer, Berlin, pp. 106-116.

Schnabel, S. 1997. Soil erosion and runoff production in a small watershed under silvo-pastoral landuse (Dehesas) in Extremadura, Spain. Geoforma Ediciones, Logroño.

Schnabel, S., Dahlgren, R.A., Moreno, G. In press. Soil and water dynamics. In Mediterranean Oak Woodland Working Landscapes. Dehesas of Spain and Rangelands of California, P. Campos, L. Huntsinger, J.L. Oviedo, P.F. Starrs, M. Díaz, R. Standiford, G. Montero (eds.), Springer, New York.

Shaw, E.M. 1988. Hydrology in practice. Van Nostrand Reinhold, London.

Swarowsky, A., Dahlgren, R.A., Tate, K.W., Hopmans, J., O’Geen, A.T. 2011. Catchment-scale soil water dynamics in a Mediterranean oak woodland. Vadose Zone Journal 10, 800-815.

Van Schaik, N.L.M.B., Schnabel, S., Jetten, V.G. 2008. The influence of preferential flow on hillslope hydrology in a semi-arid watershed (in the Spanish Dehesas). Hydrological Processes 22, 3844-3855.

Van Schaik, N.L.M.B. 2009. Spatial variability of infiltration patterns related to site characteristics in a semi-arid watershed. Catena 78, 36-47.

World Meteorological Organization 1986. ReglamentoTécnico. OMM nº 49, Geneva.


Copyright (c) 2013 Susanne Schnabel, Alvaro Gómez-Gutiérrez

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