Evaluation of surface irrigation potential areas using geospatial techniques: the case of the Nashe watershed, western Ethiopia Open Access

Irrigation is the principal strategy for raising agricultural production (Heiba et al. 2024). In Ethiopia, agriculture has a well-established role in fostering both long-term food security and economic prosperity (Hassen et al. 2024). The Ethiopian economy is highly dependent on agriculture and it directly supports about 85% of the population's livelihoods and 40% of total gross domestic product (GDP) (Asresie et al. 2015). Nonetheless, it has historically relied on rain and been a subsistence system, and it is impacted by the temporal and spatial variability of rainfall in different areas of the Ethiopian country (Adamseged et al. 2019). Water scarcity and increasing population pressure pose significant challenges to agricultural production in many parts of Ethiopia.

This led to frequent crop failures and droughts, which significantly impacted agricultural output and the nation's capacity to feed its quickly expanding population (Mera 2018). Of Ethiopia's 3.7 million hectares of arable land, only 190,000 ha (5.3%) have been submerged under irrigation (Hussien et al. 2019). Because the Ethiopian agricultural industry is not as developed as it should be and irrigation systems are still in their infancy. To address these challenges, irrigation development is crucial for enhancing agricultural productivity, increasing crop yields, and ensuring food security.

To improve modeling and decision-making about investments irrigated in land suitability, spatial information regarding land suitability for irrigation is essential (Sultan 2013; Tolera et al. 2023). Modeling agricultural land suitability can serve as a foundation for future updates on irrigation land suitability. Studies on irrigation suitability vary in terms of their geographic scope, objectives, and criteria considered, as well as the availability of spatial data for the watershed. Using a variety of criteria, numerous studies on irrigation suitability have been conducted at the national, basin, sub-basin, and watershed levels.

Like other areas of the study is on subsistence-level agricultural production. Several studies have been conducted across Ethiopia, particularly in the western and southwestern regions, focusing on the spatial evaluation of surface irrigation for agriculture to enhance rural crop productivity (Kitila et al. 2014; Moisa et al. 2022; Mitiku et al. 2024). However, little attention has been directed toward modeling land suitability for surface irrigation in the Horo Guduru Wollega Zone, specifically in the Nashe watershed. Despite the availability of abundant land and water resources, the agricultural system in this area has yet to achieve its full potential due to a lack of comprehensive information on land suitability for surface irrigation. Rain-fed agriculture is the sole practical means of producing food crops in the Nashe watershed, Horo Guduru zone. As a result, the study area experiences widespread food insecurity due to the temporal and spatial instability of rainfall.

Hence, employing geospatial techniques, the suitability of land for irrigation was assessed, considering various factors such as soil properties, topography, land cover, and water availability. Therefore, the study aimed to fill the existing research gap by evaluating the potential areas suitable for surface irrigation using geospatial technology integrated with the analytical hierarchy process (AHP) method. This approach was verified by overlaying the irrigation scheme of the region, which consists mostly of suitable lands. It provided a decision-making tool for policymakers and farmers to improve water resource management and agricultural planning in the Nashe watershed, Upper Blue Nile Basin, Western Ethiopia.

Data required for irrigation land suitability modeling, such as soil properties (soil type, soil depth, soil texture, and soil drainage), slope, land use/cover, river, and road, were collected from governmental agencies and online sources. These input data were used to generate criteria layers, which were then used to create an irrigation land suitability map (Table 1).

The study identified eight important criteria that determine the suitability of irrigation land in the watershed: land use/land cover (LULC), soil type, soil depth, soil drainage, soil stoniness, slope, and proximity to roads and water sources. These were determined by using guidelines and literature on land evaluation for agriculture.

For this study, various software packages were used. For instance, ArcGIS 10.3 software was used to analyze and visualize all the factors represented by GIS thematic layers and to produce the surface irrigation suitability map. IDRISI Selva was also used to calculate pairwise comparisons and weights of the parameters in this study. ERDAS IMAGINE 2015 and Google Earth Pro were applied for LULC classification and accuracy assessments, whereas Arc SWAT was used for watershed delineation of the study area (Table 2).

The ArcGIS Spatial Analyst Toolbox's Weighted Overlay tool, which is based on the multi-criteria decision analysis (MCDA) methodology, was used to model irrigation agricultural suitable areas. Land suitability was determined by developing and weighing the primary criteria (Ceballos-Silva & Lopez-Blanco 2003; Hamere & Teshome 2018).

Land suitability for irrigation refers to the assessment of the suitability of a particular piece of land for irrigation purposes. It involves evaluating various factors that affect the feasibility and effectiveness of irrigating the land (FAO 1976). This type of land suitability analysis is crucial for development because it provides important information about the many constraints and potential opportunities for land use that are being investigated based on land capabilities. Some key considered factors for the work were soil properties (soil type, soil depth, soil texture, and soil drainage), slope, land use/cover, river, and road. By considering these factors, agricultural land for irrigation suitability helps to determine the feasibility of implementing irrigation systems, the appropriate irrigation methods to use, and the potential productivity of the land for agricultural purposes.

An area suitable for agricultural and long-term irrigation is largely dependent on its soil (Abd-Elmabod et al. 2019). The updated Food and Agriculture Organization/United Nations Educational, Scientific and Cultural Organization (FAO/UNESCO) soil map of the East Africa classification system (FAO 1997a, b) was used to assess the soil's potential for irrigation. It was determined whether or not the soil was appropriate for irrigation using a variety of soil characteristics, including available water storage capacity, depth, drainage, and soil texture (Getahun et al. 2023). The depth of the soil profile from the top to the layer of obstacles for roots is vital for identifying land suitability for irrigation. Deep soils are important for anchoring plant nutrients and fostering plant growth.

MCE is a widely utilized technique for assessing potential land suitability for irrigation, integrating various geospatial datasets and criteria to identify suitable zones for surface irrigation. The approach typically involves combining thematic layers such as slope, soil types, soil depth, soil drainage, LULC, proximity to rivers, proximity to roads, and soil texture, each weighted based on its influence on potential land suitability for surface irrigation. The AHP is often employed to assign weights to these criteria through pairwise comparisons, ensuring the decision-making process is systematic and rational (Saaty 1980).

The MCE approach, utilizing the AHP, was applied to calculate the criteria weights for the assessment of land suitability for surface irrigation. This method follows the 1-to-9 scale proposed by Saaty (2002), which enables pairwise comparisons of selected parameters to evaluate their relative importance systematically. These comparisons facilitate the reclassification and weighting of criteria based on their significance and influence on potential land suitability for surface irrigation in the study area (Table 3).

The consistency and clarity of the pairwise comparisons were assessed using the consistency ratio (CR), with an acceptable CR value set at less than 10%. The CR was determined as the ratio of the consistency index (CI) to the random CI, ensuring reliability in the weight assignment process (Table 4). The relative importance of parameters such as slope, soil types, soil depth, soil drainage, LULC, proximity to rivers, proximity to roads, and soil texture was determined using IDRISI Selva 17 software, a tool widely used for spatial and MCDA. Through techniques like the AHP, pairwise comparisons were conducted to assign weights to each parameter, reflecting their influence on land suitability for wheat cultivation. Parameters like slope and soil texture impact physical conditions for crop growth, while proximity to rivers and roads addresses water availability and market access, respectively. These weights, summarized in Table 5, were integrated into a suitability model, enhancing the accuracy and reliability of the assessment by systematically combining environmental, physical, and socio-economic factors.

The pairwise comparison matrix applies the AHP following FAO (1997a, b) guidelines to quantify the relative importance of eight factors (Table 5). The results show that slope has the highest weight of 33%, making it the most critical factor in determining irrigation potential. This high weight is due to the significant impact of land steepness on water runoff, soil erosion, and overall water distribution in a landscape.

The next two factors are soil type, which has a weight of 23%, and soil depth, which has a weight of 16%. These two factors are crucial in determining the soil's ability to hold water and provide nutrients for crop growth. Soil drainage, which has a weight of 11%, plays a significant role in managing excess water and preventing waterlogging, which is essential for maintaining soil health and crop productivity.

Other factors like LULC (7%), distance to rivers (5%), and road proximity (3%) are less influential but still important for understanding water accessibility and human impact. Soil texture has the lowest weight of 2%, indicating that its variations have minimal impact on irrigation suitability in this study.

For instance, the results suggest that decision-makers should focus on slope, soil type, and soil depth when identifying potential irrigation areas. This focused approach enhances the weighted overlay analysis, making it more precise and supporting better agricultural planning and water resource management.

The Nashe watershed features four distinct soil types: Vertisols, Nitosols, Phaeozems, and Haplic Phaeozems, as documented by Mamo & Wedajo (2023). The majority of the area is dominated by Haplic Phaeozems, a soil type known for its fertility and suitability for agricultural purposes when properly managed. The spatial distribution of these soil types significantly influences the land's irrigation potential.

The western and northwestern parts of the watershed are identified as highly suitable for surface irrigation, likely due to favorable soil characteristics and topographic conditions. Conversely, the northern and northeastern regions show moderate to marginal suitability, reflecting less optimal but still manageable conditions for irrigation.

Soil analysis shows that Nitosols at 16.3% (12,104 ha) are very suitable with a score of 4 and are highly suitable for irrigation. They have good water storage capacity and nutrient supply and can be utilized in intensive irrigation use and therefore are agriculturally suitable for development.

Vertisols at 13.7% (10,134 ha) with a suitability of 3 are irrigable to a moderate extent. They have some disadvantages like seasonal variation and compaction, but overall their nature can be tolerable for irrigation schemes that can successfully manage these disadvantages. Otherwise, Leptosols at 12.5% (9,273 ha) with a suitability of 2 are not very suitable for irrigation. Their susceptibility to erosion and shallow depth can limit water availability and demand careful management and possible soil improvement work. Their susceptibility to erosion and shallow depth can limit water availability and demand careful management and possible soil improvement work. Haplic phaeozems dominate the area at 57.5% (42,719 ha) but are not suitable for irrigation with a score of 1 (Table 6). Hence, massive irrigation development needs to be planned for Nitosol and Vertisol areas, and alternative sources may be needed for haplic phaeozems areas. This distribution highlights the uneven potential for surface irrigation across the watershed, with more than half of the area facing significant limitations.

The findings align with previous research by Rabia et al. (2013), which similarly emphasized the variability of soil suitability for irrigation within different landscapes. The consistency of these results reinforces the validity of the methodology and highlights the importance of considering soil properties in irrigation planning.

Soil texture refers to the relative proportions of different-sized mineral particles (such as sand, silt, and clay) present in a soil sample (Hunduma & Kebede 2020). These mineral particles are the primary solid components of soil and are derived from the weathering and decomposition of rocks and minerals. The soil texture of the Nashe watershed consists of clay and silt clay, with the watershed being predominantly covered by clay (Table 7).

A surface's slope, which is often stated as a percentage, is its inclination or gradient. Slope affects runoff, drainage, erosion, and crop selection, making it crucial for the creation and management of soil. The duration of the irrigation flow, crop adaptability, erosion management techniques, and irrigation method are all significantly impacted by the land's slope gradient. When it comes to surface irrigation, the following negative impacts escalate with gradient: crop selection gets more constrained, water control becomes more challenging, erosion risk escalates, and irrigation runs become more feasible. According to FAO (1997a, b), slopes less than 15% are suitable for irrigation, according to FAO standard recommendations for evaluating slope gradient. However, slopes higher than 73% are generally not advised for surface irrigation (Table 8). The digital elevation model data of 30.5 m resolution from the Shuttle Radar Topography Mission (SRTM) was used to construct the slope and was made accessible on the Google Earth Engine repository (Moore & Hansen 2011). Table 8 defines the agricultural suitability of the different slope classes for the research areas based on the FAO guideline (FAO 1997a, b).

An additional consideration in determining whether a piece of land is suitable for irrigation is land use and land cover. For this study, six land use and land cover types were classified. According to FAO (1976), cultivated land and settlements were classified as highly suitable and moderately suitable. Additionally, grassland/shrubland and dense forest were marginally suitable and not suitable for irrigation purposes (Table 9).

The high suitability of the southwestern and northeastern regions is due to favorable soil types, slope, and water availability, which support efficient irrigation. In contrast, the central and northern regions face challenges such as poor soil conditions, drainage issues, or unfavorable topography, making surface irrigation less feasible.

These findings emphasize the importance of considering biophysical factors in land suitability assessments. Strategic planning should focus on the highly suitable areas, while alternative methods may be needed for less suitable regions to optimize agricultural productivity and water management.

These findings emphasize the importance of considering biophysical factors in land suitability assessments. Strategic planning should focus on the highly suitable areas, while alternative methods may be needed for less suitable regions to optimize agricultural productivity and water management.

Water accessibility is a key determinant in irrigation feasibility, as supported by previous studies (FAO 1997a, b; Alemu 2022). Research conducted by Avargani et al. (2022) indicates that areas within 2 km of a water source are ideal for surface irrigation due to minimal water conveyance losses and reduced operational costs. Similarly, a study by Gebremedhin & Assefa (2021) highlights that agricultural productivity significantly declines in regions where irrigation water must be transported over long distances, as farmers struggle with high pumping and distribution costs.

Moreover, the findings of this study are consistent with previous land suitability assessments conducted in Ethiopian watersheds, where proximity to rivers has been identified as a major determinant of irrigation feasibility (Kassie et al. 2022). The high suitability of areas near streams in this study further supports the argument that water availability is a primary factor influencing irrigation potential, as also noted by Teklu & Hassan (2019).

The result that areas within 0–3 km of a road are classified as highly suitable for irrigation is consistent with findings from previous studies (Worqlul et al. 2017) which highlight that reduced transportation costs and easy access to markets can significantly enhance agricultural productivity. Farmers in these areas can more efficiently transport inputs such as seeds, fertilizers, and water, as well as transport crops to markets. This accessibility supports the economic sustainability of irrigation projects and encourages greater investment in farming systems.

The moderately suitable category (3–6 km) indicates that while agricultural activities can still be supported, there are emerging challenges in terms of transportation costs and time. As distance from roads increases, logistical difficulties become more pronounced, particularly in regions where road networks are underdeveloped or poorly maintained. Studies by Teferi et al. (2024) suggest that farmers in such areas often face increased transportation costs, which can lead to a reduction in their ability to access necessary agricultural resources and markets. This can limit their ability to profit from irrigation systems, even if the land itself remains suitable for agriculture.

Areas in the marginally suitable category (6–9 km) present more significant barriers to accessibility. The findings here are consistent with Teshome & Reta (2020), who found that increased distances from roads can dramatically reduce access to inputs and markets, especially in rural regions. Logistical challenges in these areas are more severe, with delays in transportation potentially leading to crop losses and increased irrigation costs. Moreover, the added transportation costs could outweigh the benefits of irrigation, making it less economically feasible in these regions.

Finally, areas considered unsuitable (9–12 km) due to their distance from roads highlight the crucial role that accessibility plays in supporting agricultural and irrigation practices. As distances to roads increase, market accessibility declines significantly, making it difficult for farmers to transport produce and acquire necessary resources. This limits their ability to participate effectively in irrigation agriculture, leading to a lack of economic incentive to invest in irrigation systems. This result mirrors the findings of several studies (Gellie & Uzoegwu 2021), which argue that remote locations with poor road access are often the least conducive to the successful implementation of irrigation projects.

In conclusion, the analysis of road proximity emphasizes the importance of transportation infrastructure in determining irrigation feasibility. Policymakers and development agencies should prioritize improving road networks, especially in areas where agricultural potential is high but access to markets remains limited. Enhancing transportation infrastructure would reduce the costs and logistical challenges faced by farmers, fostering greater adoption of irrigation systems and promoting sustainable agricultural development. Future studies could also explore the role of road quality and maintenance in affecting transportation efficiency and its subsequent impact on irrigation practices.

This classification approach is justified by the direct relationship between road accessibility and the economic efficiency of agricultural systems. Proximity to roads plays a pivotal role in reducing the costs of transporting both inputs and outputs, as well as in ensuring timely delivery to markets. As a result, areas in the southern and some eastern parts of the Nashe watershed, which are closest to roads, were identified as highly suitable for irrigation. Conversely, the northern part of the watershed, being farther from road access, was deemed unsuitable for irrigation due to the limited market connectivity and increased transportation challenges. These classifications are consistent with established principles of market access and transportation economics, which emphasize the importance of infrastructure proximity in supporting sustainable agricultural practices.

Soil depth suitability for irrigation is an important factor to consider when assessing the feasibility and effectiveness of irrigation systems. The depth of the soil profile influences root development, water-holding capacity, and the ability of plants to extract water and nutrients. Based on the soil depth requirement of most common crops, the soil depth of the study area was divided into suitability classes to select surface irrigation potential. Rating factor was given for the value of soil depth and weighting them to evaluate the suitability of surface (gravity) irrigation potential of the study area. A rating factor values of 0–55 cm are highly suitable, 55–122 cm is moderately suitable, 122–146 cm is marginally suitable, and 146–176 cm is unsuitable (Table 10), which was adopted from FAO guidelines (Nachtergaele et al. 2000).

The potential land suitability for surface irrigation in the Nashe watershed, as assessed from eight parameters, shows that 18.9% of the study area (14,077 ha) is highly suitable, 68.8% (51,075 ha) is moderately suitable, and 12.2% (9,078 ha) is unsuitable for surface irrigation (Table 11).

The highly suitable areas, located in the western and some northeastern parts, are characterized by favorable soil types, topography, and water availability, making them ideal for efficient irrigation. These regions provide the best potential for implementing surface irrigation, as they offer optimal conditions for water distribution and crop growth.

The moderately suitable areas, which dominate the central parts of the watershed, present manageable conditions for irrigation but may require additional infrastructure or land management strategies to overcome challenges such as less ideal soil conditions or drainage issues. These areas could benefit from further development and irrigation interventions, although efficiency may be lower than in the highly suitable regions.

The unsuitable areas (12.2% of the total area), mostly located in regions with poor soil, unfavorable slopes, or limited water access, are not conducive to surface irrigation. These areas may require alternative irrigation methods or land use changes to improve their productivity or might be better suited for other agricultural practices.

These findings underscore the importance of targeted land use planning. Policymakers and agricultural planners should focus on the highly suitable areas for irrigation development while also considering alternative methods or infrastructure improvements for the moderately suitable regions. The unsuitability of certain areas should guide future agricultural and water resource management strategies to optimize the use of available resources.

This study evaluated agricultural land suitability for irrigation within the study area. The assessment was conducted by evaluating eight key parameters using the AHP approach combined with an ArcGIS environment. Based on the pairwise comparison matrix and normalized weights, the most crucial parameters for identifying irrigation suitability were: slope (33% weight), soil type (23% weight), soil depth (16% weight), and soil drainage (11% weight). These biophysical factors were found to be the most important in determining the suitability of land for surface irrigation. In contrast, other factors such as LULC (7% weight), distance to rivers (5% weight), distance to roads (3% weight), and soil texture (2% weight) were assigned lower weights in the suitability modeling. Based on the computed parameter weights, the final suitability map classified the study area into three classes: highly suitable, moderately suitable, and unsuitable for irrigation. The results showed that 18.9% of the study area was highly suitable, 68.8% was moderately suitable, and 12.2% was unsuitable for irrigation. This work provides the spatial distribution of irrigation-suitable lands but does not assess the appropriateness of these lands for specific crop suitability. Surface irrigation and sustainable agricultural development were deemed appropriate for gently sloping, predominantly cropped areas near rivers and roads, as well as dystric nitisols, well-drained soils, and clay soil areas. It is recommended that the concerned authorities further evaluate the highly and moderately suitable areas at the zonal or district level to inform the targeted implementation of agricultural irrigation.

The authors acknowledge the Ethiopian Institute of Agricultural Research and the Department of Earth Science College of Natural and Computational Science Wollega University Nekemte Campus for the existing facilities to conduct this research.

The authors agreed to publish the manuscript on Water Supply.

No funding was received for this research.

M.D. and M.B.M. participated in research design, document analysis, and manuscript writing. T.A. participated in data collection, methodology, data analysis, and interpretation. M.B.M. participated in research design, literature review, data analysis, and final draft edition. All authors read and approved the final manuscript for publication.

All relevant data are available in the manuscript.

The authors declare there is no conflict.