Rainwater management for increased productivity among small-holder farmers in drought prone environments
Introduction
Water productivity in rainfed agriculture will have to increase dramatically over the next generation if food production is to keep pace with population growth. Almost the total population growth (95%) and the bulk of present under-nutrition occur in tropical developing countries, of which a large proportion depends on rainfed agriculture for their livelihoods. In sub-Saharan Africa, e.g., over 60% of the population depend on rain-based rural economies, generating in the range of 30–40% of country GDP (World Bank, 1997). Rainfed agriculture in sub-Saharan Africa is practised on approximately 95% of the agricultural land (the remaining is under irrigated agriculture) and will remain the dominant source of food production during the foreseeable future (Parr et al., 1990). In general yields from rainfed agriculture are low, in many parts of the water-scarce tropical world oscillating around 1 t ha−1 (Rockström, 2001). There is ample evidence to suggest that the low productivity in rainfed agriculture is more due to sub-optimal performance related to management aspects than to low physical potential (Agarwal and Narain, 1997; Benites et al., 1998; Rockström and Falkenmark, 2000; SIWI, 2001). This means that in the developing countries experiencing the most rapid population growth, dependence on rainfed agriculture operating at a sub-optimal level is high. Furthermore, it has been estimated that there is limited new land to put under agriculture (McCalla, 1994; Young, 1999), contrary to the last three decades in sub-Saharan Africa when the bulk of increased food production originated from expansion of agricultural land. There is thus a growing pressure to increase agricultural productivity through raised yields per unit soil and unit water.
This paper presents the agro-hydrological rationale to focus on water productivity in rainfed agriculture, identifies key management challenges in the attempt to upgrade rainfed agriculture, and presents some field experiences on system options for increased water productivity in small-holder farming in drought prone environments. Implications for watershed management are discussed, and the links between water productivity for food and securing of water flow to sustain ecosystem services are briefly analysed. The focus is on semi-arid and dry-sub-humid tropical agro-ecosystems where the importance of increase in water productivity is highest.
Section snippets
Rainwater management––the rationale
A broad approach to water productivity in land management that covers both irrigated and rainfed agriculture has implications on water resource management. Conventionally, focus on global, regional and national freshwater resources and withdrawals has been on the stable and accessible surface and sub-surface flow of water in rivers, lakes and groundwater, the so-called blue water branch in the hydrological cycle (UN, 1997; Cosgrove and Rijsberman, 2000). Blue water is withdrawn for direct blue
Hydroclimatic challenges
Water related problems in rainfed agriculture in water scarcity prone tropics are often related to high intensity and large spatial and temporal variability of rainfall, rather than low cumulative volumes of rainfall (Mahoo et al., 1999; Rockström et al., 1998; Sivakumar and Wallace, 1991). Rainfall is highly erratic, and rain often falls as convective storms, with high rainfall intensity and extreme spatial and temporal variability. Coefficients of variation range from 20–40%, increasing with
Supplemental irrigation
Bridging dry spells through supplemental irrigation of rainfed crops can be an interesting option to increase water productivity at production system level (Oweis et al., 1999; SIWI, 2001). Supplemental irrigation in small-holder farming systems can be achieved with water harvesting systems that collect local surface runoff (sheet, rill and gully flow) in small storage structures (100–1000 m3). Water harvesting, broadly defined as the concentration of surface runoff for productive purposes, has
System implications––balancing water for food and nature
Increasing withdrawals of water in rainfed and irrigated agriculture may have negative implications on water availability to sustain direct human withdrawals and indirect withdrawals to sustain ecosystem services. As shown by Rockström et al. (1999) almost the totality of global green water flow (88%) is already at present used to sustain biomass growth in the World’s biomes. While agriculture (rainfed and irrigated) annually accounts for an estimated 7000 Gm3 yr−1, forests and woodlands require
Conclusions and discussion
There is no doubt that the immense challenge of doubling food production over the next 25 years in order to keep pace with population growth, requires increased attention to water productivity and rainwater management, simply by making the best use of the local water balance. As shown in this paper, even in water scarcity prone tropical agro-ecosystems, there is seemingly no hydrological limitation to double staple food crop yields in rainfed small-holder agriculture. Furthermore, evidence
References (38)
- et al.
Water harvesting for supplemental irrigation of cereal crops to overcome intra-seasonal dry-spells in the Sahel
Phys. Chem. Earth, Part B Hydrol. Oceans Atmos.
(2000) - et al.
Seasonal rainfall partitioning under runon and runoff conditions on sandy soil in Niger. On-farm measurements and water balance modelling
J. Hydrol.
(1998) - et al.
Dying Wisdom. Centre for Science and Environment
(1997) - et al.
Rain water management for dryspell mitigation in semi-arid Kenya
E. Afr. Agric. Forestry J.
(1999) - Barron, J., Rockström, J., Gichuki, F., Hatibu, N., Dry spell occurrence and potential impact on maize yields: Rainfall...
- Benites, J., Chuma, E., Fowler, R., Kienzle, J., Molapong, K., Manu, J., Nyagumbo, I., Steiner, K., van Veenhuizen, R....
- et al.
World Water Vision––Making Water Everybody’s Business––Report to the World Water Council
(2000) Historical review of no-tillage cultivation of crops
- Elwell, H.A., 1993. Development and adoption of conservation tillage practices in Zimbabwe. In: FAO Soils Bulletin, vol...
- et al.
The Negev, the Challenge of a Desert
(1971)