It was hypothesized that RWH could reduce the susceptibility of rainfed cropping systems to the high inter-seasonal variability in the start of the rainy season. Overall, this analysis
shows little potential for RWH to increase the flexibility of cropping calendars. Rather, the future selection of better sowing dates based on long-term climate data observations and projections, as well as in-season rainfall monitoring and forecasts would be more beneficial in reducing risk. While RWH does significantly reduce water stress on crops and improve soil moisture, it cannot fully address the issue of low rainfall totals throughout the growing season, as well as more frequent dry spells of long duration. Current planting dates around June 15th or later seem already optimized to take advantage of an early rainy season onset, while mitigating the impacts of a later season onset.
Greater availability of relevant meteorological information, through forecasts and real time rainfall measurements for example, could lead to improved management decisions at the field level. Chapter 5 already discussed the implications for an innovative farmer of access to daily rainfall measurements in his decision-making process. This analysis re- iterates the need for wider access to long-term rainfall time series, as well as daily in-season rainfall data, to help farmers optimize cropping calendars under a changing climate, amongst other things. The simple methodology to determine agronomical rainy season onset presented in Chapter 5 (Ibrahim et al., 2012) could be adapted for use at the farm level un- der a changing climate.
6.4.4 Shifting sowing dates to adapt to climate change
The 2050s represent an interesting period for climate change analyses, as it is projected to be the first time where climate will depart from its recent natural variability (Mora et al., 2013). Indeed, it was shown in Chapter 4 that GCMs project robust increases in the frequen- cy of dry spells lasting longer than 15 days over the Sahel, as well as changes in the growing season distribution of maximum duration dry spell events. Changing cropping calendars to address the latter changes was suggested earlier as a possible adaptation strategy. However, in the case of sorghum in West Africa, the changes in the distribution of maximum duration dry spells were not found to be statistically significant, and therefore a shift in sowing dates was not found to be particularly beneficial, nor was it detrimental, in the case of Ziga. Oth- erwise, in some instances, growing varieties with a shorter growth cycle could be beneficial.
6.5 Conclusions
In this Chapter, the different roles in situ RWH can play in current and future agricultural systems of Northern Burkina Faso were investigated using integrated hydrological and crop modelling. Overall, while the identification of the causes of the changes in water availability by farmers was erroneous, it was linked to real changes in soil moisture and crop water stress.
Importantly, it has been shown that while zaï pits have been termed RWH strategies, they are in fact integrated soil and water management strategies. Farmers indeed use zaï pits in combination with manure, but also with a range of other management strategies such as stone lines which also reduce overland flow velocity. These form complex, integrated, and optimized natural resources management systems which cannot fully be modelled in SWAT. Hence, benefits such as the protection of seeds from being flushed away in early season runoff events, the relative ease of removal of the soil surface crusts through digging small pits rather than ploughing when faced with a lack of agricultural implements or animals, or the fact that fertilizers are being concentrated for direct uptake by the plants, can easily be overlooked.
It is likely that in situ RWH will be a key strategy to adapt to climate change due to its ability to maintain (or increase, in the case of zaï with manure) soil water holding capaci- ty in the longer term. RWH was found to continue to improve yields in the 2050s, with sor- ghum yield increases of 10% on average across GCMs. However, an overall significant de- crease in yields associated with a changing climate renders the benefits from increased wa- ter availability through RWH marginal. An overall increase in high intensity rainfall events, leading to greater surface runoff totals and equivalently higher soil water erosion is of con- cern for the sustainability of agricultural production in the region.
No one solution will be able to address all climate change impacts on crop produc- tion in Northern Burkina Faso, and a range of adaptation strategies will be required to ad- dress the different changes in the climate. Unlike what is often thought, adaptation will not need to occur in a distant future. In fact, as the widespread adoption of improved soil and water management practices has taken several decades and serious institutional investments (c.f. Chapter 5), planning ahead and current investments will be required. This will involve the continued spread of in situ rainwater harvesting to mitigate the long-term impacts of soil water erosion, but also the development of strong meteorological networks to allow farmers to implement adequate short-term coping strategies such as optimized planting dates in the future.
Chapter 7
From impacts to transformation: A critical review of climate
change adaptation literature in the field of agriculture and the
framing of this thesis
7.1 IntroductionThroughout this thesis, an attempt has been made to assess the potential of rainwater har- vesting strategies as an adaptation strategy to climate change. In Chapter 7, I undertake a meta-analysis of the agricultural adaptation literature, with a view of putting analyses in previous Chapters into the broader context of climate change adaptation research. The bibli- ometric analysis points to some significant changes occurring in the use of the term adapta- tion in the climate change literature. The approach used here provides further insight into why these changes might be taking place, and why it is important to acknowledge them to avoid omitting important implications for food security and to reduce the risk of maladapta- tion. Hence, I also investigate how global food security is being addressed within the agri- cultural adaptation literature, and what are the implications.
First, the methodology developed to analyse the very large body of adaptation lit- erature is described, along with its limitations. Key findings are then highlighted with re- spect to their relationship with topics addressed throughout this thesis (e.g. uncertainties and perceptions). Subsequently, the first part of the discussion addresses the implications of the bibliometric analysis findings for global food security. This opens up a critical assessment of the methodological approach selected for this thesis, and whether or not it has fully reached its stated objectives. Finally, suggestions for innovative methodological approaches based on this integrated learning process are made.