Rainfall–interception–evaporation–runoff relationships in a semi-arid catchment, northern Limpopo basin, Zimbabwe

Abstract

Characterizing the response of a catchment to rainfall, in terms of the production of runoff vs the interception, transpiration and evaporation of water, is the first important step in understanding water resource availability in a catchment. This is particularly important in small semi-arid catchments, where a few intense rainfall events may generate much of the season's runoff. The ephemeral Zhulube catchment (30 km 2 ) in the northern Limpopo basin was instrumented and modelled in order to elucidate the dominant hydrological processes. Discharge events were disconnected, with short recession curves, probably caused by the shallow soils in the Tshazi sub-catchment, which dry out rapidly, and the presence of a dambo in the Gobalidanke sub-catchment. Two different flow event types were observed, with the larger floods showing longer recessions being associated with higher (antecedent) precipitation. The differences could be related to: (a) intensity of rainfall, or (b) different soil conditions. Interception is an important process in the water balance of the catchment, accounting for an estimated 32% of rainfall in the 2007/08 season, but as much as 56% in the drier 2006/07 season. An extended version of the HBV model was developed (designated HBVx), introducing an interception storage and with all routines run in semi-distributed mode. After extensive manual calibration, the HBVx simulation satisfactorily showed the disconnected nature of the flows. The generally low Nash-Sutcliffe coefficients can be explained by the model failing to simulate the two different observed flow types differently. The importance of incorporating interception into rainfall-runoff is demonstrated by the substantial improvement in objective function values obtained. This exceeds the gains made by changing from lumped to semi-distributed mode, supported by 1 000 000 Monte Carlo simulations. There was also an important improvement in the daily volume error. The best simulation, supported by field observations in the Gobalidanke sub-catchment, suggested that discharge was driven mainly by flow from saturation overland flow. Hortonian overland flow, as interpreted from field observations in the Tshazi subcatchment, was not simulated so well. A limitation of the model is its inability to address temporal variability in soil characteristics and more complex runoff generation processes. The model suggests episodic groundwater recharge with annual recharge of 100 mm year -1 , which is similar to that reported by other studies in Zimbabwe.Key words HBV; interception; Limpopo basin; semi-arid hydrologyRelations précipitation-interception-évaporation-écoulement dans un bassin versant semi-aride (nord du Limpopo, Zimbabwe) Résumé La caractérisation de la réponse d'un bassin versant aux précipitations, en termes de production d'écoulement par rapport à l'interception, la transpiration et l'évaporation, est un premier pas important pour la compréhension de la disponibilité des ressources en eau dans un bassin. Ceci est particulièrement im...

Temporal and spatial changes of rainfall and streamflow in the Upper Tekezē–Atbara river basin, Ethiopia

“…This Pettitt technique has been widely used to detect time change points in the hydro-climatic data (e.g. Ma et al, 2008;Love et al, 2010;Gao et al, 2011;Zhang et al, 2011;Gebremicael et al, 2013;Tekleab et al, 2013).…”

“…The length of the records vary from station to station, whilst all gauging stations with at least 30 years of continuous and relatively good quality of observed data were taken into account. A 30-year record is a reasonable minimum for applying statistical trend analyses of rainfall (Love et al, 2010;Longobardi and Villani, 2009). …”

“…The impact of climate change on hydrology varies from place to place. For example, Ma et al (2008) for the arid region of north-west China, Zhang et al (2011) for China, Zhao et al (2015) for the Wei River basin of China, Love et al (2010) for the Limpopo River of southern Africa and Abeysingha et al (2015) for the Gomti River basin in northern India found that a decreasing trend of rainfall resulted in a significant reduction in streamflow. In contrast, Masih et al (2011) in the Zagros mountains of Iran, Wilk and Hughes (2002) in southern India and Abdul Aziz and Burn (2006) in the Mackenzie River basin of Canada reported that a trend of increasing rainfall has significantly increased river flows.…”

On the value of combined event runoff and tracer analysis to improve understanding of catchment functioning in a data-scarce semi-arid area

“…However, experimental hydrology and processrelevant studies in the predominantly data scarce semi-arid regions of SSA or Central Asia are, due to mostly logistical and financial constraints, less widespread (e.g. Sandström, 1996;McCartney et al, 1998;Kongo et al, 2007;Wenninger et al, 2008;Mul et al, 2009, Love et al, 2010Makurira et al, 2010), thus limiting our understanding of catchment scale hydrological functioning and, maybe more importantly, thereby inhibiting sustainable water resources strategies and policies in such data scarce areas.…”

An experiment to gauge an ungauged catchment: rapid data assessment and eco-hydrological modelling in a data-scarce rural catchment

“…Thus the approach is one possible alternative to, for example, Monte Carlo simulations with HBV-type models under similar conditions (Love et al 2010).…”