Soil hydraulic information for river basin studies in semi-arid regions

Abstract Water retention and hydraulic conductivity characteristics of the soil are indispensable for hydrological catchment modelling and for quantifying water limited agricultural production. However, these characteristics are often not available for regions and data scarcity for tropical zones is even bigger than for temperate zones. Use of pedotransfer functions which translate soil survey data into soil hydraulic characteristics is an interesting alternative in such cases. In this study, existing pedotransfer functions are identified and their performance is tested for the Limpopo river basin in Africa where distribution of limited water resources is a major challenge. The well performing pedotransfer function developed by Hodnett and Tomasella (2002) was used to translate the map units of the soil and terrain (SOTER) database for southern Africa into hydrological response units. Ten functional soil characteristics were calculated and clustering resulted in a reduction of the 713 SOTER map units for the Limpopo river basin to 14 hydrological response units. The resulting hydrological response unit map provides the required spatial information on soil physical input data, both water retention and hydraulic conductivity, for hydrological modelling of the river basin as well as for assessment of agricultural production. The developed procedure is an attractive approach for other, similar data scarce environments.