Climate change and agriculture: Impacts and adaptation options in South Africa
Introduction
The impacts of climate change on agriculture are a key reason for concern. It is now widely acknowledged that adaptation would help to alleviate the worst of the potential impacts. In this paper, we take adaptation beyond the usual crop management and selection, and investigate the effects of expanded irrigation and accelerated technological progress. We focus on a single country, South Africa, and analyze whether an economy can be studied in isolation from its trading partners.
Climate change would modify agricultural productivity through five main factors changes in precipitation, temperature, carbon dioxide (CO2) fertilization, climate variability, and surface water runoff [1]. Crop production is directly influenced by changes in precipitation and temperature. Precipitation is the main source of all freshwater resources and determines the level of soil moisture, which is a critical input for crop growth. Moreover, precipitation is the main contributor of yield variability because it is much more variable than potential crop evapotranspiration, the factor that determines crop water requirements. Based on an econometric analysis of US agriculture, Reilly et al. [2] found that higher precipitation levels lead to a reduction in yield variability. Therefore, higher precipitation will reduce the yield gap between rainfed and irrigated agriculture, but it may also have a negative impact if extreme precipitation causes flooding and water logging [3].
Temperature and soil moisture determine the length of the growing season and control the crop development and water requirements. In general, higher temperatures will shorten the frost periods, promoting cultivation in cool-climate marginal croplands. However, in arid and semi arid areas, higher temperatures will shorten the crop cycle and reduce crop yields, because higher temperature leads to increased crop water requirements [4]. Higher atmospheric concentrations of carbon dioxide enhance plant growth and increase water use efficiency (CO2 fertilization), especially for the C3 crops, and so affect water availability [5], [6], [7].
Climate variability, especially changes in rainfall patterns, is particularly important for rainfed agriculture. Soil moisture limitations reduce crop productivity and increase production risk in rainfed farming systems. Although the risk of climate variability is reduced by the use of irrigation, irrigated farming systems depend on surface runoff or groundwater availability, which are subject to change under climate change. Increased climate variability and droughts will affect livestock production as well, through disrupting feedstock supply or even limited water for animal drinking.
Following the rapid expansion of manufacturing and mining industries over last several decades, agriculture׳s share in GDP in South Africa is barely 4 percent (2001–2002 period). However, despite the small share of agriculture in the overall economy, the sector accounts for almost 10 percent of total employment in the country and about one-third of total production is exported [8]. Agriculture in South Africa is often perceived as a successful sector, and most of the agricultural production is dominated by medium- to large-scale farms. However, South Africa has a dual agricultural economy, comprising well-developed commercial farms and a large number of small-scale subsistence farms. Commercial farms are mainly large-scale, capital intensive and export oriented, accounting for around 90 percent of the total agricultural production and covering about 86 percent of the country׳s cropland. Subsistence farms, in contrast, rely on traditional methods of production and are labor intensive, employing around 86 percent of the total farm labor [9].
Despite the global scale of climate change and the fact that food products are traded internationally, climate change impacts on agriculture have mostly been studied at the farm [10], the country or the regional level [11], [12], [13]. Studies of climate change impacts at the global level indicate that the inclusion of CO2 fertilization is likely to offset some of the potential welfare losses generated by climate change [14], [15], [16]. Global models have also been used to study the role of adaptation in adjusting to new climate conditions [11], [17], [18]. The results suggest that farm-level adaptations might mitigate negative impacts induced by climate change.
However, none of these studies include water as an explicit factor of production. The present approach, based on the GTAP-W model [19], avoids this limitation. By introducing irrigation water as a factor of production in irrigated agriculture, the model supports the analysis of expected physical shortage/abundance of water supply for irrigated crops (blue water). In addition, changes in rainfall (green water) patterns are modeled by changes in the productivity of rainfed and irrigated land. The distinction between rainfed and irrigated farms is crucial, because rainfed and irrigated agriculture face different climate risk levels.
The aim of this paper is to assess climate change impacts on agricultural production worldwide, with a special emphasis on South Africa and its connections to the rest of the world. Furthermore, two possible adaptation strategies to cope with climate change in South Africa are considered: expansion of irrigated areas and increase in agricultural yields. The analysis is based on the GTAP-W model, a global computable general equilibrium (CGE) model that allows for a rich set of economic feedbacks and for a complete assessment of the welfare implications of alternative development pathways. Unlike an earlier version [20], the revised GTAP-W model distinguishes between rainfed and irrigated agriculture and thus explicitly incorporates water resources.
The remainder of the paper is organized as follows: the next section briefly describes the GTAP-W model and the baseline simulations. Section 3 focuses on climate change scenarios and impacts on global agriculture in 2050. In Section 4, the efficacy of two adaptation scenarios for South Africa is discussed. Section 5 contains discussion and conclusions.
Section snippets
Modeling framework
Economic models of water use have generally been applied to look at the direct effects of water policies, such as water pricing or quantity regulations, on the allocation of water resources. In order to obtain insights from alternative water policy scenarios on the allocation of water resources, partial and general equilibrium models have been used. While partial equilibrium analysis focus on the sector affected by a policy measure assuming that the rest of the economy is not affected, general
Climate change scenarios: changes in agricultural productivity and area
In our analysis future climate change impacts on global agriculture are based on four climate change scenarios from projections of two general circulation models (CSIRO and MIROC)8 using two IPCC Special Report on Emissions Scenarios (A1B, B1).9
Adaptation scenarios
Development of irrigation and improvements in agricultural productivity have proven to be effective tools for poverty alleviation and economic growth [38], [39], [40]. Calzadilla et al. [13] evaluate the efficacy of both measures as adaptation options to cope with climate change in Sub-Saharan Africa as a whole. They found that an increase in agricultural productivity achieves better outcomes than an expansion of irrigated areas, due to the overall low initial level of irrigated areas in the
Discussion and conclusions
There is large uncertainty about the future effects that climate change may bring to nature and people. This analysis explores the potential implications of climate change on global agriculture based on four climate change scenarios from two general circulation models (CSIRO and MIROC) and two IPCC SRES emission scenarios (A1B, B1). Furthermore, two possible adaptation strategies to cope with climate change in South Africa are considered: expansion of irrigated areas and improvements in
Acknowledgments
We gratefully acknowledge the financial support of the OECD Environmental Directorate. We would also like to thank Elisa Lanzi and Nicholas Kingsmill at the OECD for comments and feedbacks.
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