This document summarizes a study modeling soil and water dynamics in northern Ghana. Researchers measured rainfall and estimated runoff at three sites to develop regression relationships between rainfall and runoff. They also used a soil water balance model to estimate changes in soil water storage based on rainfall, runoff, drainage, and actual evapotranspiration. The results showed strong correlations between rainfall and runoff. Soil moisture storage increased more in wet and normal years compared to dry years. More detailed validation work is still needed using spatially available weather, soil, and climate data from the study sites.

1. MODELING SOIL AND WATER DYNAMICS IN NORTHERN GHANA
Davie M. Kadyampakeni1, Tim Ellis2, Yoro Sidibe3
1International Water Management Institute, Accra, Ghana
2Environment South Land, New Zealand
3International Water Management Institute, Accra, Ghana (Currently with the World Bank, Washington DC, USA)
Corresponding author email: d.kadyampakeni@cgiar.org
Introduction
Soil water management is critical for sustainable crop production,
particularly in drought-prone environments. A range of strategies can be
used to address spatial and temporal soil water availability for crop
water uptake and improved yield productivity. This paper presents the
results from field and simulation studies of rainfall and run-off
monitoring in rainfed maize-based cropping systems in northern Ghana.
Materials and Methods
Study site: The study was done in:
• Sazie (long.: 2°21'0.20"W, lat.: 10°16'6.24"N, alt.: 280 m)
• Kalphohin (long. 0°49'30.84"W, lat.: 9°25'1.23"N alt.: 172 m)
• Duko (long.: -0.85o; lat.: 9.55o; alt.: 181 m)
Rainfall and runoff estimation: Rainfall was measured using rain gauges
and runoff was estimated using run-off pits in selected fields.
The soil water balance model and empirical modeling:
• Long-term weather data was sourced from Wa weather station and
Tamale Airport.
• Soil water balance components through change in soil water storage,
∆S, is given as:
∆S = IR + R – RO – D – AET
where:
- ∆S is the change in soil moisture storage (m3),
- AET is actual evapotranspiration (m3),
- R is rainfall (m3),
- RO is surface runoff (m3),
- D is drainage (m3).
Figure 2. Soil water balance model components (runoff, actual
evapotranspiration (AET) and soil moisture storage) for northern Ghana.
• The field studies in the three regions of northern Ghana resulted in
the development of regression rainfall-runoff relationships for
understanding soil water dynamics in situ.
• Estimation of size of water conservation/storage structures could be
designed based on long-term rainfall-runoff relations to increase
timely crop water availability and reduce spatial losses of water
through surface runoff.
Conclusions
The Africa Research In Sustainable Intensification for the Next Generation (Africa RISING) program comprises three research-for-
development projects supported by the United States Agency for International Development as part of the U.S. government’s Feed the
Future initiative.
Through action research and development partnerships, Africa RISING will create opportunities for smallholder farm households to move out
of hunger and poverty through sustainably intensified farming systems that improve food, nutrition, and income security, particularly for
women and children, and conserve or enhance the natural resource base.
The three projects are led by the International Institute of Tropical Agriculture (in West Africa and East and Southern Africa) and the
International Livestock Research Institute (in the Ethiopian Highlands). The International Food Policy Research Institute leads an
associated project on monitoring, evaluation and impact assessment.
www.africa-rising.net
Results
• There were strong correlations between runoff and rainfall (R2=0.75-
0.97), for both Leptosols and Plinthosols under 750 mm rainfall
season.
• Deep and medium depth soil showed increments in soil moisture
storage by ranges of 175 to 200%, 117 to 167% and 28 to 31% during
dry, normal and wet years, respectively.
• On average, soil moisture storage was 30% and 22% in normal and wet
years over dry year.
More detailed work will be required to validate these observations
using a process-oriented and spatially available weather, soil and
climatic data for the sites involved in the study.
Recommendation
Figure 1. Rainfall-runoff relationships for the sites in Northern (left) and Upper
West (right) regions of Ghana.