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5: Climate Outlook

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5

Climate Outlook

The earth’s climate is changing. Farmers, especially those working on rainfed projects in the drier parts of the world, have likely already felt the effects of global climate change, in the form of shifted rainy seasons, heavier storms, or extended dry periods during the growing season. In fact, smallholder farmers and laborers working on rainfed farms in the developing world are among those most directly affected by global climate change. At the same time, the ingenuity and traditional environmental knowledge that small farmers possess will be a key tool for adaptation to new climate realities.

Changes in water availability – in the form of rainfall patterns, green water storage, surface water flows, and water quality – are some of the most visible effects of climate change. Because the unpredictability of these resources is only expected to increase in as time goes by, it is important to learn to anticipate and adapt to new conditions before their effects become too pronounced.

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8: Crop-focused Strategies: Using Available Water Wisely

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8

Crop-focused Strategies: Using

Available Water Wisely

The plant also has a role to play in water productivity. Crop management techniques can enhance the plant’s ability to use soil water efficiently, further reinforcing the benefit of the soil and water management practices described in

Chapters 6 and 7. Cropping systems can also be designed to encourage drought resistance and mitigate the harmful effects of dry periods. Drought resistance ultimately improves water productivity because it increases the potential for producing crop yields in seasons disrupted by dry spells.

Cropping patterns have a considerable impact on water productivity. Crop layouts and plant combinations can be calibrated to produce a maximum amount of product (or income) from within available water supplies. Often, this involves rotating between different plant varieties with complementary water and nutrient requirements.

Drought resistance can also be enhanced by selecting drought-resistant cultivars, and by training the physiological adaptation mechanisms of existing crops to access scarce soil water or improve the efficiency of the conversion process that transforms it into product.

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2: Goals of Agricultural Water Management

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2

Goals of Agricultural Water

Management

Water is a vital component of every agricultural project. In addition to supporting plant growth, water is critical to maintaining soil health and promoting the overall ecological well-being of the land, which are essential in ensuring the long-term viability of the farm. In this book, the term soil and water management practices is used to designate the range of farming practices that influence the way in which water flows through the farm environment and is transformed into crop yields. This category includes methods of water application, but also cropping systems, soil management practices, and land use patterns. The purpose of this publication is to define and explain sound practices for managing water in the cultivation of field crops. While the management of soil and water resources is equally important in other agricultural categories such as livestock rearing, aquaculture and forestry, these remain outside of the scope of this book.

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7: Rainwater Harvesting

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7

Rainwater Harvesting

Unfortunately, it is not feasible for a farmer to decide to ‘turn on the rain’ to water his fields at the time of his choosing and in the amount needed. To maximize his water supply, he will need to effectively capture all of the rain that falls on the field, and if possible intercept and collect excess rainwater falling on the surrounding area. In purely rainfed farming where no blue water sources are exploited, these are the only available water inputs. Even when surface or groundwater is accessible for use as supplemental irrigation, it is most efficient to first optimize the effectiveness of rainwater before moving water from other sources.

Rain that drains from the field instead of infiltrating becomes runoff. Left unchecked, runoff leads to significant water loss, wasting up to 40% of rainwater inputs.1 Rain runoff is also the principal cause of soil erosion. Rather than allowing runoff to leave the field, landforms such as basins, bunds, and gullies can be used to intercept and direct it toward the base of crop plants where it is needed. The use of land-­shaping to capture, direct, and concentrate rainwater is commonly known as rainwater harvesting (RWH). Because they discourage the rapid outflow of runoff, rainwater harvesting techniques are also erosion prevention measures.

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Preamble to Part 2

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Preamble to Part 2

Although agricultural literature devotes much of its attention to irrigation methods and equipment, the vast majority of farms across the world, and especially across the tropics, are exclusively rainfed. Globally, rainfed agriculture represents 80% of all cultivated farmland, on which 60% of the world’s food crops are grown.1 In sub-Saharan Africa over 95% of all farmland is purely rainfed, and a full 90% of all crops are produced in this way. Rainfed farming also dominates in Latin America (90% of farmed land), South Asia (60%), East Asia

(65%) and the Middle East and North Africa (MENA) countries (75%).2 Most of the world’s grain crops are purely rainfed.3

These statistics, however, reflect a misconception that there is a clear dividing line between ‘rainfed’ and ‘irrigated’ agriculture projects. In fact, the distinction is rarely so cut and dry. As introduced in Chapter 1, farming includes a continuum of water management practices spanning from purely rainfed to purely irrigated agriculture, and most projects lie somewhere between these two extremes. Just as many rainfed projects incorporate some degree of irrigation in order to mitigate dry spells, irrigated agriculture projects should also strive to make the best use of available rainfall in order to minimize blue water withdrawals.

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