Research

Planning of system innovations in watersheds

Spatial mapping of environmental and hydrological determinants in Pangani and upper Ewaso Ng'iro north river basins, Africa

PhD thesis (4.51 MB)

In the Sub-Saharan Africa (SSA) region, about 95% of agriculture is mainly rain-fed, which means that majority of the population here depend on rainfall and agricultural productivity for their survival. Moreover, about 41% of the agricultural land is located in the dry areas of this region, out of which a mere 2% is irrigated. This implies that for a foreseeable future, it is rain-fed agriculture that will be the dominant source of food for the rapidly increasing population in SSA.

The growth of the agricultural sector in many countries of SSA has been reported to be low in the last decade despite the fact that this sector is recognized as a priority in poverty reduction. This is because of low availability of soil moisture for crops resulting from poor management and ineffective utilization of rainwater. It is estimated that in many farming systems, more than 70% of the rain falling directly on a crop-fields is lost as non-productive evaporation or flows into sinks before it can be used by plants. Therefore, efforts should be made to promote optimal utilization of available rainwater by adopting appropriate water system innovations (WSIs) in order to alleviate water scarcity and improve rural livelihoods in these areas.

It is well documented that food security in most water scarce areas of SSA is not only threatened by increased water shortages particularly for crop production purposes but also by climate change which is likely to become even worse with increases in rainfall variability being predicted. In SSA, water-related problems particularly in rain-fed agriculture are often related to high intensity short duration of rainfall with large spatial and temporal variability, rather than to low cumulative amount of rainfall. Such rainfall patterns result in high risk for meteorological droughts and intra-seasonal dry spells that lead to low crop yields and sometimes total crop failures. Although the situation appears to be desperate, adaptation of water systems innovations such as rainwater harvesting (RWH) could serve as a remedy since they have proven to be a promising potential technology for upgrading rain-fed agriculture by improving water availability for crop production.

The main challenge that needs to be aggressively confronted in these regions is how to reduce the impacts of such climatic disparities and cushion farmers against their effects on rain-fed agriculture. This could be achieved by increasing water productivity through promoting and implementing suitable and innovative water use systems that can improve soil moisture content and thus enhance crop yields.

Improved water productivity (crop-per-drop) in SSA can be secured in different ways in both rainfed and irrigated agriculture by improving infiltration potential through adoption of WSIs with soil and water conservation measures. This would also reduce the destructive overland flows that tend to cause severe erosion damage in large parts of these areas. However, research done on the performance of the already existing rainwater harvesting and management systems, in SSA shows that most of RWH storage systems such as farm ponds have poor performance due to high water losses. The poor performance of has led to low adoption rates and to a larger extent, abandonment of these systems by the farmers. It is in this regard that this project is being conducted to address some of these concerns of sustainable land and water productivity through development of a mapping methodology for WSIs with regard to sustainable water resource planning and management. The methodological framework will facilitate the identification of suitable areas for appropriate and suitable WSIs for up-scaling purposes, geared towards upgrading rain-fed agriculture in SSA.

The methodology will employ integrated technologies of quantitative remote sensing and GIS tools for spatial data capture and analysis. Trade off analysis will also be carried out to assess the impacts of up-scaling of the identified suitable WSIs to the basin scale on the area hydrology and also the sharing of the water resources between the upstream and downstream users within the basin. The information generated from this study could be used to raise awareness and guide policy decisions on the contribution of WSIs towards meeting the Millennium Development Goals (MDGs) in SSA.

The research context

This project is being conducted in two pilot Basins (Ewaso Ng’iro North in Kenya and Pangani in Tanzania) at watershed and Basin scales. A suitable Spatial Decision Support System (SDSS) will be identified and modified to facilitate the identification of potential areas for various WSIs at the lowest scale using a Multi-Criteria Evaluation (MCE) approach in which biophysical, hydrological and socio-economic characteristics of the area under investigation will be explored within a GIS environment. The procedure will then be applied to watershed and Basin scales in which spatial distribution of these different WSIs will be obtained.

Project goal

This research envisages in contributing to the knowledge base required in formulating sustainable water and land resources management strategies for water scarce river basins aimed at enhancing water productivity and improve food security particularly in the semiarid lands of SSA and therefore, consequently contribute to the on-going global dialogue on water for food and environment to meet the already stipulated MDGs.

Research overall objective

The main objective of this study is to provide a rapid GIS-based analytical technique for assessing the suitability of various water systems innovations (WSIs) within the dry areas of SSA.

Specific objectives

In order to realise the above set goal, the following specific research objectives are envisaged:

• Determine/identify both bio-physical and socio-economic factors that influence the suitability of potential WSIs.
• Develop and evaluate a suitable DSS for selecting suitable sites for WSIs.
• Determine and rank potential and suitable sites for WSIs at watershed scale.
• Evaluate the spatio-temporal productive water use (Evapotranspiration) in relation to the existing WSIs at watershed scale using quantitative remote sensing.
• Identify a suitable approach for equal water allocation among different users in the basin under different water resources development options.
• Evaluate the impacts of land use change emanating from the upscaling the suitable WSIs on the basin Hydrology.

The study basins in Tanzania.

The study basins in Kenya.

Promoting Rainwater Harvesting (RWH) initiatives by CETRAD for reafforestation efforts in the Ewaso Ng’iro Basin geared towards enhancing its environmental integrity.

Data acquisition equipments in the study area.

Different water systems innovations (WSIs) found in the study areas.