Introduction
Rainfed agriculture occupies 80% of the global cultivated area and produces 60% of global crop output. With growing concern over water scarcity limiting the scope to achieve future food security through increasing production from irrigated land, attention has shifted to the wide gap between actual and potential yield which exists in rainfed systems in many developing countries (particularly in sub-Saharan Africa). In the past decade there has been growing recognition of the scope to close this yield gap by improving 'green water' productivity thereby improving food security and rural livelihoods. Rainwater harvesting (RWH) is seen as an effective technical green water management intervention that is widely claimed to increase yields by 100% to 200% compared to conventional rainfed agriculture. Despite these claims, adoption by farmers themselves remains slow and hence impacts on crop production and rural livelihoods marginal. This paper argues that this gap between expectation and reality is due to an over-simplified view of rainfed agriculture and the potential impact of green water management. Current hypotheses regarding the crop gains possible through improved green water management do not give adequate recognition to the wider environmental and livelihood context within which rainfed agriculture sits, or factors (such as vulnerability/risk context) that influence the behaviour of farmers.
Methods
In Burkina Faso government and NGOs have been promoting the use of a range of soil and water conservation technologies, including RWH, since the 1970s. We present mixed methods research examining the experience in Burkina Faso over the past few decades to investigate the potential of RWH to close the yield gap in small-scale rainfed agriculture and improve livelihoods. Quantitative modelling of crop water productivity allows simulations of the long-term effects on sorghum yields in several case study locations to investigate variability and risk. This is coupled with the analysis of primary qualitative data collected during two extended periods of fieldwork in Burkina Faso in 2012 and 2013. Farmers from three case study sites were purposefully selected to participate in a range of data collection activities to gain insight on the factors that support or constrain their ability to adopt and benefit from RWH technologies.
Results and Discussion
Findings indicate that unpredictable and highly variable rainfall poses a high risk to rainfed crop production for small-scale farmers in the case study sites, but water is not the only factor that can limit crop yield. Availability of and access to a range of assets required for production can also lead to reductions in crop yields (and water productivity). At community level, increases in production were limited by high population pressure that has already led to the exploitation of all available land for cultivation. At farm level, limited or no access to basic agricultural inputs, such as compost/fertiliser, improved seeds and labour during key growing stages, limit the crop gains farmers achieve via RWH. Observations suggest that the distribution and availability of increases in crop production, food and income due to RWH are highly unequal between farmers. RWH provides substantial increases in food security and income only for the wealthier farmers in the case study villages, who are able to invest in the technologies on a larger scale and have a larger asset base. Although agriculture continues to be the primary activity for households, it is just one of a portfolio of diverse activities used by men and women to achieve livelihood outcomes. A range of on and off-farm activities (both locally and outside of the villages) are conducted to gain additional income for a variety of household needs, particularly in the dry season. Such livelihood portfolios are highly dynamic and changes to the type and extent of activities may be made in response to both endogenous and exogenous factors such as household composition, climate, markets and credit availability. This variety in and change to the portfolio of activities farmers engage in impacts their ability to adopt RWH and the contribution the technology provides to livelihoods over time. This research helps to understand both the opportunities for contributions to crop production and household livelihoods from RWH, as well as the limitations. The range of factors identified that have the potential to reduce benefits farmers achieve via RWH are likely to reduce motivation of others to adopt the technology, particularly poorer farmers who often experience multiple agricultural and livelihood constraints. Consideration of the role of RWH within farmers' wider environmental and livelihood context demonstrates that the technologies operate within a highly complex system. The potential impact of RWH on crop production and livelihoods cannot be assessed using studies that examine green water productivity in isolation from the rest of the farming or livelihood system.
Conclusion
Although RWH techniques may help to alleviate the negative influence of unpredictable and highly variable rainfall on rainfed crop production, their use does not result in the achievement of reliable yield increases at the widely claimed 100-200 percent level. This research has identified that various factors lead to crop losses for small-scale rainfed farmers, particularly for those in relatively poorer households. The design of future agricultural interventions which aim to increase green water productivity needs to include consideration of the whole farming system and provide increased availability of and access to the whole package of agricultural inputs necessary to minimise crop losses. Such a holistic approach allows for a deeper understanding of the potential impact of how farmers integrate the technologies into their farming and livelihood systems. This research highlights that farmers' behaviour and choices are not necessarily in line with assumptions made by advocates of RWH and this behaviour needs to be more accurately represented in assessments of the potential impact of RWH and other green water management projects. Future research on RWH and other green management water strategies also requires more analysis on their benefits over the long-term. A more in-depth examination of the relationship between risk and yield increments is needed to more reliably determine the contribution that green water management strategies can realistically make to increasing crop production and improving livelihoods.