Assessment of suitable land for surface irrigation using spatial information systems: Case of Bilate River Basin in the Rift Valley Lakes Basin, Ethiopia

Abstract

Identifying the limited available resource, use of improved irrigation technology and better water resources management have been suggested as mechanisms for increased production. To optimize the agricultural production, knowing the available land for irrigation is mandatory. This study aimed to assess the suitable land for surface irrigation using different spatial parameters (normalized difference vegetation index, soil, slope, proximity, rainfall deficit, and land use). Land suitability was assessed by considering the individual parameters and then by overlaying. The overlay suitability analysis was performed by using weighted overlay tool within spatial analyst tool in ArcGIS. After excluding the irrigation constraints suitable land for surface irrigation was identified. Based on the individual parameters analysis the normalized difference vegetation index gives the largest land size which is 95 % of the total land as suitable. While the slope factor gives the lowest figure which is 57 % of the total land is suitable for irrigation. The weighted overlay analysis, gives only 28.46 % of the total land in the basin was suitable for surface irrigation. More than 93 % of this suitable land is grouped in to small scale while only about 7 % is used for medium to large scale irrigation.

Introduction

With a rapid rate of population increase there will be a competition for the limited available resources (water and land), which will result in high pressure on arable land to increase food production. With continuing population growth and limited potential to increase suitable cropland, efficient irrigation becomes an increasingly important tool to ensure sufficient global supply of food in the future (Wichelns and Oster, 2006, Sauer et al., 2010). The shortage of food in Africa continent is ever rising since 2014, reach nearly one-fifth of the population. The weather extremes are one of the factors which play significant role to unsustainable production of cereals (FAO, 2021) through rain fed farming system. As Irrigation a basic strategy to alleviate poverty and hence food security, transforming the rain-fed agricultural system into the combined rain-fed and irrigation agricultural system is believed to be the most prominent way of sustainable development. According to Kadigi et al (2019), it is only six million hectare (4 %) of Sub-Saharan Africa's total cultivated area is irrigated, while this is even lower to 2.08 % of the cultivable land in Ethiopia in 2018 as to World Bank's collection of development indicators compiled from officially recognized sources (Yonas et al 2022).

In Ethiopia, there is no consistent and reliable inventory and well-studied and documented (Belay and Woldeamlak, 2013) with regards to water and irrigations related potentials in the Ethiopian context. MoA (2011) reported about 10–12 % of the total irrigable potentials are under production using traditional and modern irrigation schemes (Haile and Kasa, 2015). According to the World Bank's collection of development indicators compiled from officially recognized sources, Ethiopia's agricultural irrigated land was 2.08 % percent in 2018. Identifying the limited available resource, use of improved irrigation technology and better water resources management have been suggested as mechanisms for increased production. To optimize the agricultural production, knowing the available land for irrigation is mandatory.

The Bilate river basin is among the highly populated with erratic rainfall basins of Ethiopia, that relays on the traditional method of food production using rain fed agriculture. As a result of that, the people in some parts of the basin expect the aids from the government every year. Hence, the agricultural production has to be improved through the use of irrigation improve the food security caused by insufficient output from these rain fed systems (Worqlul et al., 2015).

The process of land suitability classification is the appraisal and grouping of specific areas of land in terms of their suitability for defined uses (FAO, 1976). This study has therefore conducted to assess the suitable land for surface irrigation using spatial parameters such as; normalized difference vegetation index (NDVI), soil type, slope, river proximity, rainfall deficit, town proximity, road proximity and land use. NDVI, use as an indicator in irrigable land suitability assessment is not common, (Gebre et al., 2021, Yonas et al., 2022) however it will give an indication to the soil fertility which is a very important parameter for crop production, in addition to the physical parameters.