Rainfall‐discharge relationships for a monsoonal climate in the Ethiopian highlands

Abstract

This study presents a simple rainfall-discharge analysis for the Andit Tid, Anjeni, and Maybar watersheds of northern Ethiopia. The Soil Conservation Research Programme (SCRP) established monitoring stations in each of these sites during the 1980s, with climate and stream flow measurements being recorded up to the present. To show how these data could be used to provide insight into catchmentlevel runoff mechanisms, simple linear relationships between effective precipitation and runoff are developed for each watershed, with the conclusion that all three watersheds exhibit consistent hydrologic behaviour after approximately 500 mm of cumulative effective seasonal rainfall has fallen since the beginning of season. After the 500 mm rainfall threshold is reached, approximately 50% of any further precipitation on these watersheds will directly contribute to catchment runoff.

Improving efficacy of landscape interventions in the (sub) humid Ethiopian highlands by improved understanding of runoff processes

“…Precipitation, discharge and storm event sediment yields are available from 1988-1994, 1996-2004, and 2008 (Table 1). 16901984-1993-2013Liu et al, 2008Guzman et al, 2013;Tilahun et al, 2013a,b;Elkamil, 2014;Tebebu et al, 2014;Bayabil et al, 2015 Maybar 113 Phaeozems and Phaeozems associated to Lithosols 12101988-19941996-2004Liu et al, 2008Bayabil, 2009;Bayabil et al, 2010;Guzman et al, 2013 Andit Tid 481 Andosols and Regosols 15001986-19921994-2001Liu et al, 2008Engda, 2009;Guzman et al, 2013;Tilahun et al, 2013b Debre Mewi 95 Nitosols and Vertisols 1240-2014Abiy, 2009Tebebu, 2009;Tebebu et al, 2010;Zegeye et al, 2010;Tilahun, 2012;Langendoen et al, 2013;Dagnew et al, 2014;Tebebu et al, 2014;Zegeye et al, 2014;Dagnew et al, 2015;Tilahun et al, 2015 The Andit Tid watershed, situated 180 km northeast of Addis Ababa at 39 • 43 ′ E and 9 • 48 ′ N, covers 481 ha ( …”

“…The hydrological similarity over 14 day periods in watersheds can be seen by comparing the long-term discharge and sediment concentrations of the three SCRP watersheds (Figures 2, 3, 4), namely Andit Tid, Anjeni, and Maybar, located hundreds of kilometers apart. Liu et al (2008) showed that for cumulative seasonal effective rainfall of 500 mm or more the proportion of rainfall that becomes runoff is remarkably the same. Figure 2 which is redrawn from Liu et al (2008) shows that for all three watersheds, the discharge over a 14 day period as a function of the effective rainfall (defined as precipitation minus potential evaporation).…”

“…Liu et al (2008) showed that for cumulative seasonal effective rainfall of 500 mm or more the proportion of rainfall that becomes runoff is remarkably the same. Figure 2 which is redrawn from Liu et al (2008) shows that for all three watersheds, the discharge over a 14 day period as a function of the effective rainfall (defined as precipitation minus potential evaporation). The trend lines for each of the three exhibit a linear relationship of effective precipitation and amount of watershed outflow.…”

“…Although the explanation of this linear relationship varies (e.g., Chandler and Walter, 1998), it seems that since rainfall intensity does not affect the relationship, direct runoff from a fixed source area with a shallow ground water table (either perched or regional) is the most likely explanation (Steenhuis FIGURE 2 | Relationship between 14-day discharge and effective precipitation (precipitation minus potential evaporation) after 500 mm. of cumulative effective precipitation occurring since the beginning of the rainy phase for three watersheds in the Ethiopian highlands (Liu et al, 2008). The dotted lines are the regression lines for each of the watersheds with the same colors as the symbols.…”

Analyzing runoff processes through conceptual hydrological modeling in the Upper Blue Nile Basin, Ethiopia

“…The SWAT model is based on the Soil Conservation Service (SCS) runoff curve number approach, where the parameter values are obtained empirically from plot data in the United States with a temperate climate. Liu et al (2008) studied the rainfall-runoff relationships for the three Soil Conservation Research Project (SCRP) watersheds (Hurni, 1984) in the Ethiopian highlands and showed the limitations of using such models, developed in temperate climates, in monsoonal Ethiopia. Adjusted runoff curve numbers for steep slopes with natural vegetation in northern Ethiopia were reported by Descheemaeker et al (2008).…”