Abstract
Abstract. With a growing world population and a trend towards more resource-intensive diets, pressure on land and water resources for food production will continue to increase in the coming decades. Large parts of the world rely on rainfed agriculture for their food security. In Africa, 90% of the food production is from rainfed agriculture, generally with low yields and a high risk of crop failure. One of the main reasons for crop failure is the occurrence of dry spells during the growing season. Key indicators are the critical dry spell duration and the probability of dry spell occurrence. In this paper a new Markov-based framework is presented to spatially map the length of dry spells for fixed probabilities of non-exceedance. The framework makes use of spatially varying Markov coefficients that are correlated to readily available spatial information such as elevation and distance to the sea. The dry spell map thus obtained is compared to the spatially variable critical dry spell duration, based on soil properties and crop water requirements, to assess the probability of crop failure in different locations. The results show that in the Makanya catchment the length of dry spell occurrence is highly variable in space, even over relatively short distances. In certain areas the probability of crop failure reaches levels that make rainfed agricultural unsustainable, even close to areas where currently rainfed agriculture is successfully being practised. This method can be used to identify regions that are vulnerable to dry spells and, subsequently, to develop strategies for supplementary irrigation or rainwater harvesting.
Highlights
Increasing population causes increasing pressure on the available water resources, which represents a major challenge in water management (Falkenmark, 1997)
The results show that in the Makanya catchment the length of dry spell occurrence is highly variable in space, even over relatively short distances
This study shows the spatial structure of dry spells of Tanzania: long wet spells in the north-eastern highlands and long dry spells in the centre part of the country (Tilya and Mhita, 2007)
Summary
Increasing population causes increasing pressure on the available water resources, which represents a major challenge in water management (Falkenmark, 1997). In the case of sub-Saharan Africa, population is growing rapidly and a shift to a more land and water resource-intensive diet is expected (Savenije, 1998, 2000; WWAP, 2009), requiring more use of the resources. These resources vary both spatially and temporally, alternating wet and dry years, with large variations between different locations (e.g. Mul et al, 2009). Average food production per capita is declining (Love et al, 2006). Demographic pressure and the limited availability of arable land force people to move from areas where conditions are favourable to areas and ecosystems where conditions are less favourable or marginal (Enfors and Gordon, 2007)
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