Climate change adaptation through rainwater harvesting to enhance food security in Diamaré, Cameroon

Since the 1800s, human activities have been the main driver of climate change, primarily due to the burning of fossil fuels such as coal, oil, and gas (UN 2023). In fact, according to the most recent Intergovernmental Panel on Climate Change Sixth Assessment Report (IPCC 2023), human activities, principally through emissions of greenhouse gases, are unequivocally responsible for global warming with the global surface temperature reaching 1.1 °C above pre-industrial levels.

About 15% of today's anthropogenic greenhouse gas emissions are believed to come from agricultural sources (Akinnagbe & Irohibe 2014). While being a major contributor to climate change, agriculture is the most vulnerable to climate disasters (FAO 2011). Nowhere are its impacts more evident than in the agricultural sector. Climate change results in increasing temperatures, changing rainfall patterns, and more frequent and intense extreme weather events such as droughts, cyclones, and floods, which hamper agricultural productivity in several ways (Fakava 2012). These extreme weather events have direct effects on crop growth and their need for water, groundwater recharge, and the water cycle, as well as soil fertility, water supply for irrigation, and the prevalence of pests and diseases, which causes a huge loss in agricultural production (Yadav et al. 2020).

Within the context of scarce water resources for agriculture, rainwater harvesting (RWH) constitutes a promising alternative that has been studied by different disciplines in recent years (Njoya et al. 2022). It guarantees a reasonably constant supply of water to crops by harnessing rainfall over a catchment surface and storing it for use at deficient periods. However, RWH appears to not have been widely adopted by farmers in the Far North Region of Cameroon (Cheo et al. 2014). There is limited literature on the impact of RWH on crop yields in Cameroon. This study therefore seeks to investigate the feasibility of RWH as an adaptation mechanism in the Far North Region of Cameroon. It was hypothesized that RWH has a significant impact on crop yields in the Diamaré Division, Far North Region of Cameroon. The study objectives were as follows: (i) to determine the current water sources used by farmers in Diamaré, (ii) to determine the degree of RWH adoption by farmers in Diamaré, (iii) to ascertain the various types and levels of RWH practiced by farmers in Diamaré, (iv) to identify the challenges faced by farmers in the adoption of RWH, in Diamaré, (v) to estimate the fraction of crop water requirements deficit met through RWH, in Diamaré, and (vi) to assess the impact of RWH on crop yields in order to develop a strategic framework for improving access to water in Diamaré Division, Far North Region of Cameroon.

Diamaré Division, situated in the plains of the Far North Region of Cameroon at coordinates 10°35′37″N and 14°18′52″E, spans an area of 4,665 km² with a population density of 137.7/km² (Figure 2). It comprises nine sub-divisions, namely, Bogo, Dargala, Gazawa, Maroua I, Maroua II, Maroua III, Meri, Ndoukoula, and Petté with Maroua as its capital (City Population 2017). Maroua I, II, and III are urban settings. The Diamaré plains fall within the Sudano-Sahelian ecological zone of Cameroon, characterized by a semi-arid climate (Molua & Lambi 2006). This climate exhibits a dry season extending from October to May and a brief rainy season from June to September, with an annual rainfall average of 700 mm. Temperature differentials ranging from 27 to 41 °C are significant, and the rainy season and dry season nights (December–January) generally experience cooler conditions. Relative air humidity varies with altitude (Fita Dassou et al. 2015).

The study concentrates on rural smallholder farmers in the Diamaré Division, Far North Region of Cameroon. Using a purposive sampling method, Meri, Gazawa, Bogo, and Petté sub-divisions were used for the study, given they are entirely agriculture-based. In order to determine the current water sources used by farmers, the degree of RWH adoption by farmers, the types and levels of RWH practiced by farmers, and the challenges faced by farmers in the adoption of RWH, a total of 150 farmers were surveyed. Questionnaires were administered by interviewers with the help of a research assistant to counter language barriers.

In order to assess the impact of RWH on crop yields, a farm experiment was conducted in Maroua I. A 500 m² parcel of farmland was chosen based on convenience as well as its favorable characteristics (Figure 3). The nature of the soil lithology was homogeneous vertisol for the entire plot. Vertisols are tropical soils with good agricultural and engineering potentials and cover over 1,200,000 hectares in North Cameroon (Tamfuh et al. 2018). The piece of land used for the study was covered in clay soil with a clay-loamy soil type that is ideal for garden plants.

While other water harvesting techniques such as infiltration pits or recharge aquifers exist, a rooftop collection and tank storage technique was preferred for the experiment because it allows for the measurement and control of water supply, which are crucial for the experiment. An existing building located at the edge of the farm was used to establish a rooftop RWH infrastructure with an approximate catchment area of 15 m² (Figure 4). A 6-m-long gutter was installed to collect the rainwater. Using a Poly Vinyl Chloride (PVC) pipe, the collected water was conveyed into a 1000-L plastic tank for storage.

To determine the irrigation water requirement met through harvested rainwater, data on the water requirement of each crop used was collected from secondary data sources. According to FAO (2022), the standard grass crop grown in a semi-arid climate with a mean temperature above 25 °C needs approximately 9 mm of water per day. Based on these parameters, crop water needs for the four crops concerned were estimated as follows.

As depicted in Table 2, the initial investment for RWH consists of renting farmland, the cost of acquiring a used water tank, the cost of installing a rooftop water harvesting system and acquiring a watering can. For crops grown without RWH, the initial investment consists of renting farmland only. The annual cost consists of the costs of seeds, manure, pesticides, and cost of labor, which was the same for both cultivation under RWH and no RWH conditions. The annual revenue was determined by multiplying the quantity of cucumber output from each section by the unit price (price per kg of cucumber). The discount rate adopted represents the operational interest rate in Cameroon. The water harvesting system adopted is assumed to serve for a period of 15 years.

Farming in Diamaré is practiced both during the rainy season and the dry season. In the rainy season, the results from the survey reveal that all farmers (100%) depend on rainfall for agriculture. These results are compatible with the study by Ntali et al. (2023), who pointed out that agriculture is primarily rainfed. During this season, the main crops cultivated are maize, millet, cotton, sorghum, beans, groundnuts, cowpeas, rice, and potatoes. During the dry season, the main crops cultivated are onion, sorghum, pepper, tomatoes, okra, carrots, and other vegetables. The farmers mainly used collected rainwater, boreholes, and wells to meet their crop water needs. However, this is effectively the case only in the rainy season. Dry season farming capitalizes on other water sources such as boreholes and wells, which has rarely been discussed by previous researchers. It is therefore crucial to take into consideration water sources used by farmers in the dry season, as over 41.3% of farmers in Diamaré are involved in counter-season farming.

Results from the survey show that 85.3% of farmers practice either rooftop and/or surface RWH. This drifts away from most other works that present contrary findings. Mtyelwa et al. (2022) have it that RWH adoption by smallholder farmers is very low in the rural areas of Ethiopia and South Africa. Furthermore, while most farmers (74.7%) practice rooftop RWH, just 42% of farmers practice surface runoff water harvesting. The findings also reveal that factors that greatly influence farmers' adoption of RWH are income/finance, level of technology, and complexity of RWH systems. This perfectly complements the results of Nji & Fonteh (2002) as concerns factors influencing RWH adoption in the Mandara Mountains of the Far North Region of Cameroon.

Just like in the work of Mwenge Kahinda & Taigbenu (2011), finance is the most common challenge limiting the widescale adoption of RWH for agriculture in Diamaré. A greater number (71.3%) of the farmers surveyed revealed that RWH for agriculture is an expensive investment that they cannot afford. Furthermore, a majority (56%) of the farmers point out that their water storage capacity is limiting their ability to store rainwater. A significant proportion of farmers also find it difficult to realize (55.3%) and maintain (48.7%) RWH infrastructures. Another striking challenge is that over 41.3% of the farmers do not know what RWH technique to use in their farms.

The farm experiment demonstrated that RWH effectively supplemented crop water needs for all crops except cowpeas (Table 3). This aligns with the finding of Sacolo & Mkhandi (2021) that RWH could meet 45% of crop water requirements in the Lubombo Plateau. Okra had an approximate growing period of 81 days during which its water requirement was 738 mm. Owing to insufficient rainfall, okra had an irrigation water need of 144 mm, which was met through RWH. Cucumber had an approximate growing period of 81 days, during which its water requirement was 664.2 mm. Owing to insufficient rainfall, cucumber had an irrigation water need of 70.2 mm, which was met through RWH. The lettuce was transplanted after attaining 2 weeks of growth. It therefore had an approximate growing period of 60 days on the experiment farm, during which its water requirement was 558 mm. Rainfall was however limited to 324 mm. Thus, lettuce had an irrigation water requirement of 234 mm, which was met through RWH. Cowpeas, conversely, had a lower water requirement. While it had a water requirement of 475.6 mm, rainfall during its growing period of 81 days was 594 mm. This means the crop had sufficient water with the support of RWH. Excess water has a negative impact on the crop's growth, as will be seen in the following section.

Parkash et al. (2021) reported that cucumber plants with a smaller number of leaves will have reduced yield due to reduced photosynthesis ability. Vide et al. (2023) have shown that cucumber yield is affected by irrigation. It can be deduced from Figure 8 that RWH has a positive impact on the growth and development of cucumbers. On the 24th day of growth, crops from both sections had an average of about eight leaves each. However, on the 54th day, cucumber crops that received harvested rainwater had an average of 36 leaves each, while those that did not receive rainwater had an average of 34 leaves each. The impact is, however, insignificant given the minimal difference between the means of crops that received rainwater and crops that did not, with a p-value of 0.732 at a 95% confidence level.

Furthermore, for lettuce crops, there was no significant difference between the number of leaves for crops that received harvested rainwater and those that did not receive harvested rainwater at a 95% confidence level (p = 0.937).

Cowpeas, conversely, have a very low water requirement, hence their suitability for the Diamaré region. As a result, they received just a little harvested rainwater during the first days of growth after which they were left to grow under normal conditions. Figure 8 shows that on the 24th day of growth, the crops that received harvested rainwater had an average of 9 leaves, while those that did not had an average of 8 leaves. By the 44th day of growth, neither of the crops was receiving harvested rainwater but there was still a difference in the number of leaves. Crops that did not receive rainwater had more leaves than those that did. This suggests that more water than required was supplied. The impact was however insignificant given the minimal difference between the means of crops that received rainwater and crops that did not. The insignificance is justified by the p-value (0.709), which is greater than 0.05 at a 5% level of significance.

From Figure 9, it can be seen that cucumber crops that received harvested rainwater had an average stem size of 13.01 cm, while those that did not had an average stem size of 10.98 cm. Therefore, crops that received additional harvested rainwater had comparatively larger stems than those that did not. The difference was significant given the p-value (0.008), which is less than 0.05 at a 5% level of significance. The results presented in Table 4 show that cucumber crops that received harvested rainwater produced fruits with an average length of 21 cm and diameter of 76.7 cm, while cucumber crops that did not receive harvested rainwater produced fruits that had an average length of 19.5 cm and diameter of 72 cm. This means that RWH has a positive impact on the size of the fruit produced as well. Despite the obvious positive effect of RWH on cucumber, the impact was not significant (0.218) at a 95% confidence level.

Table 3

Crop water requirement, rainfall, and irrigation water need

View Large

Unlike the other plants, the effect of supplemental water supply on lettuce plants through RWH was measured using leaf size. From Figure 9, it can be seen that on the 10th day of crop growth, lettuce crops that received harvested rainwater had an average leaf area of 30.38 cm² each, while those that did not receive harvested rainwater had an average leaf area of 28.83 cm². This was the case until the 40th day of the crop growth. Lettuce plants that received harvested rainwater had an average leaf area of 110.32 cm², while those that did not had an average leaf area of 106.71 cm². RWH, therefore, had an impact on the yield of lettuce plants. However, further analysis using ANOVA revealed that the difference in the sizes of lettuce leaves was not statistically significant at the 95% confidence level (p = 0.751).

For cowpeas, Figure 9 shows that crops that received harvested rainwater on the 34th day of growth had an average stem diameter of 8.23 cm, while those that did not, had an average of 9.16 cm. By the 44th day of growth, neither of the crops was receiving harvested rainwater but there was still a difference in the stem diameter. Cowpea crops that did not receive rainwater had larger stems (10.29 cm) than those that did (9.95 cm). This impact was, however, insignificant given the minimal difference between the means of crops that received rainwater and crops that did not. The insignificance is justified by the p-value (0.557), which is greater than 0.05 at a 5% level of significance. These results complement the works of Wanjira & Peris (2016), which revealed that RWH is more suitable for dry season farming through irrigation of the land. Thus, the decline in rainfall amounts in the study area is not significant enough to result in impaired growth of cowpea.

From Table 5, it can be seen that adopting rooftop RWH for the cultivation of cucumber in the rainy season is worthwhile given it has a higher net present value of $1,147.43, unlike cultivation under no RWH conditions. Thus, adopting rooftop RWH for cucumber cultivation in the rainy season by smallholder farmers is economically viable in the long run.

This study aimed to assess the impact of RWH on crop yields toward food security in Diamaré, Far North Region of Cameroon. Experimental results show that the crops grown under RWH conditions have better and faster growth and development rates while producing larger outputs, except for cowpea which revealed contrasting results. Cowpea is a drought-resistant crop that is suitable for cultivation in semi-arid regions. It has a low water requirement and will not produce well if given much water. Therefore, the crop water requirement is a crucial determining factor for the adoption of RWH for agriculture. Farmers should only consider RWH when their crop water needs cannot be met by direct rainfall. Based on a cost–benefit analysis performed for cucumber cultivation, the study found rooftop water collection and storage in tanks for irrigation to be economically viable in the long run for smallholder farmers. Therefore, rooftop RWH by farmers to supplement crop water needs in the rainy season during dry spells is recommended. Moreover, smallholder farmers can also adopt other cost-effective RWH technologies such as half-moon, contour bunds, terracing, and infiltration pits.

The authors wish to acknowledge support from the African Union and the Pan African University of Water and Energy Sciences, Including Climate Change (PAUWES) for awarding study scholarship to the primary author. The authors express profound gratitude to the Global Water Partnership–Central Africa (GWP-CAf) Regional Secretariat for their continuous support during the research project. Acknowledgment is also extended to Alliance Citoyenne pour le Développement et l'Éducation à l'Environnement (ACEEN), for facilitating access to rural farmers and aiding in data collection in the Far North Region.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.