Evaluating in situ water and soil conservation practices with a fully-coupled surface-subsurface hydrological model in Tigray, Ethiopia

Water scarcity is a serious problem in many rainfed agricultural systems, particularly in the semi-arid to dry subhumid tropics. In situ water and soil conservation (WSC) practices are known to improve rainwater partitioning, especially if developed to suit a given climate, soil type as well as crops. This study evaluates the potential of using a fully coupled surface-subsurface process based model (HydroGeoSphere) to simulate in detail rainwater partitioning as affected by in situ WSC practices currently under study on Vertisols in Tigray, Ethiopia and to evaluate the treatments in terms of rainwater partitioning. In the terwah+ (TER+) practice, contour furrows of about 0.2 m wide and 0.1 m deep are created at 1.5 m intervals between permanent broad beds to collect excess water while in derdero+ (DER+), permanent raised beds of 0.6 m width with furrows of about 0.2 m wide and 0.1 m deep are created to prevent water logging and collect excess water that would otherwise runoff. The plus sign (+) in both practices represents retaining at least 30% of crop residue after a cropping season, minimum tillage of the beds and crop rotations to comply with the principles of conservation agriculture. Comparison was done with the conventional tillage practice (CT) in which no contour furrows are made and at least three tillage practices are carried out with complete removal of crop residue. Field plots were permanently kept since 2005 although this study utilized measured surface runoff and moisture content for 2010 for model parameterization, and 2011 data for model verification. The model accurately reproduced measured surface runoff (e.g. in DER+: Nash-Sutcliff model efficiency E = 0.79) and soil moisture content (DER+: E = 0.83). Runoff depth was always lowest under DER+ followed by TER+ and significantly higher in CT . Simulated rootzone water storage was highest under DER+ practice, followed by TER+ and least under CT. Simulated transpiration, evaporation and drainage out of the rootzone were all higher under DER+ and TER+ compared to CT. The study concludes that DER+ and TER+ have positive effects on runoff reduction but recommends improvement of these practices, as was demonstrated with the calibrated model. The model proved to be a promising and versatile tool to assess the impact of WSC practices on rainwater partitioning at the field scale.

Publication year:2013