Vulnerability of Sri Lanka tea production to global climate change

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  • VULNERABILITY OF SRI LANKA TEA PRODUCTION TO GLOBAL CL IMATE CHANGE

    M.A. WIJERATNE Tea Research Institute

    Research Advisory and Extension Centre Ratnapura, Sri Lanka

    Abstract. The tea industry is Sri Lanka's main net foreign exchange earner and source of income for the majority of laborers. Tea yield is greatly influenced by weather, and especially by droughts, which cause irreparable losses because irrigation is seldom used on tea plantations. At the other extreme, heavy rains erode top soil and wash away fertilizers and other chemicals. Inthe recently published Sri Lanka country report on climate change, it was reported that the island will experience extreme rainfall intensities and wanner temperatures as a result of climate change. The possibility of a 10% increase inthe length of dry and wet seasons per year in the main plantation area was also indicated. Thus both drought damages and soil losses intea production areas will increase inthe years to come. An analysis of the results oftield experiments with weather data shows that increases in temperature, soil moisture deficit, and saturation vapor pressure detlcit in the low elevations will adversely affect growth and yield of tea. Reports have also shown that about 30 cm of soil has already been eroded from upland tea plantations. Under these circumstances, the tea industry in Sri Lanka is clearly vulnerable to predicted climate changes, and subsequently greater economic, social, and environmental problems. This paper discusses the various aspects of the adverse effects of climate change on Sri Lanka's tea industry.

    Key words: Sri Lanka, agriculture, tea

    1. Introduction

    Although industrial exports such as textiles and garments bring in a higher percentage of foreign exchange, a~-iculture is the highest net foreign exchange earner in Sri Lanka. Of the agricultural exports, tea alone contributes about 15-25% of the total exchange earnings and, hence, plays a key role in the Sri Lankan economy. About 30% of the employees of the public sector (government and semigovernment) are manual workers on estates, and the majority of these are employed on tea plantations. Moreover, about 239,000 tea small holdings also generate a large proportion of employment opportunities in the country. Accordingly, more than 700,000 workers and their families are dependent on the tea industry. These figures show the importance of the tea industry to the social and economic stability of Sri Lanka.

    In spite of the expansion of the small holdings sector, in Sri Lanka, the total area of tea plantations has decreased since the 1930s, i.e., from about 0.44 to 0.23 x 10 s ha. The decline in the estate sector tea lands began early in the 1960s, because of low productivity brought about by soil and bush debilitation. Many of the midcountry (600-1,200 m elevation) tea plantations have now become marginal, warranting crop diversification. Adversities of weather and poor management practices have been blamed for this situation; changes in the microclimate in tea plantations after shade removal during the early 1960s have also affected the productivity of the tea bushes (Fuch, 1989). Some adverse effects of the nationalization of the plantations in the 1970s, such as the neglect of agricultural practices, contributed to the decline in the estate sector production (Fuch, 1989).

    Being a rainfed plantation crop in Sri Lanka, tea depends greatly on weather for optimal growth. Therefore, changes in weather conditions would undoubtedly affect tea production. The relationship between tea yield and weather has been discussed by many researchers (e.g., Devanathan, 1975; Kandiah and Thevadasan, 1980; Carr and Stephens, 1992). The

    Water, Air, and Soil Pollution 92" 87-94. 1996 Kluwer Academic Publishers. Printed in the Netherlands.

  • 88 M.A. WIJERATNE

    findings of this study differ from those of the Sri Lanka country report (ADB, 1994). This could be due to the different models used to predict tea yield. It is generally accepted that an increase in temperature increases tea yield, and this relationship has been used in many models. But recent findings show that at higher temperature regimes (greater than 25-26 C), the increase in temperatures reduces tea yield.

    Droughts inflict irreparable losses to the tea industry and hence to the economy of Sri Lanka. The consequences of the droughts in 1983 and 1992 are good examples (Central Bank, 1983; 1992). The decline in production due to drought in early 1983 was about 4% over the previous year, and the drought in 1992 reduced tea production by about 26% compared to that of 1991. It also increased the costs of production by 19%, depriving the country of about 3 billion rupees (US$70 million) of foreign exchange. Total production in 1991 and 1992 was 240.7 and 178.9 10 ~ kg, respectively, and the latter was the lowest production recorded since the end of the 1950s (Figure 1). These figures show the magnitude of the loss that could be incurred by adversities of weather.

    Heavy rainfall also causes considerable damage to tea plantations through soil erosion, poor growth due to lack of sun, and increases in disease incidence. Poorly covered old seedling tea fields, pruned tea fields, and young tea fields during the first two years are more vulnerable to soil erosion due to inadequate ground cover. It has been estimated that more than 30 cm of top soil has already been lost from Sri Lanka's tea plantations, especially in the uplands (Krishnaraj ah, 1985). Landslides also adversely affect plantations and endanger the lives of workers on the hilly slopes.

    2. Climate Change and Methods

    According to climate change scenarios, the increases in global atmospheric CO 2 concentrations and temperatures by 2100 could be in the range of 600-700 ppm and 1.0-3.5 C, respectively,

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    Fig. 1. Total tea production and average yield in Sri Lanka.

  • VULNERABILITY OF SRI LANKA TEA PRODUCTION 89

    compared to 1990, depending on different scenarios of variations in greenhouse gas emissions (CO2, CH4, N20 ) and oceanic changes (Houghton et al., 1996).

    The consequences of climate change will differ from one country to another. In the recently published Sri Lanka country report (ADB, 1994), it was shown that Sri Lanka will experience frequent droughts, wanner spells, and extreme rainfall events as a result of the climate change. Scenarios &temperature changes for Sri Lanka show an increase in temperature of 0.4-3.0C by 2070 (ADB, 1994). Moreover, climate change scenarios presented for Sri Lanka have shown that the frequency and severity of such extreme weather conditions may increase, and thus affect the agriculture sector. It is also indicated that there will be a 10% increase in the length of dry and wet seasons per year in the main tea plantation area. Although an increase in rainfall is predicted, any significantly favorable impact on tea plantation agriculture is unlikely because of increased evaporation losses brought about by high temperatures and the possibility of the distribution of rainfall being erratic or uneven (ADB, 1994).

    In many other countries, vulnerability assessments on different economically and socially important areas are being conducted to inform policy makers about suitable adaptation measures that could be implemented. Hence, it has become a current need to address the possible impacts of global climate change on the tea industry in Sri Lanka.

    In this study, the effects of environmental factors on growth and yield of tea were studied using data on annual variation of climatic factors and yield parameters of tea. The relationship between the climatic factors and tea yield was analyzed using linear regression analysis.

    3. Results and Discussion

    As described previously, since there is no irrigation, tea yield is greatly influenced by weatherl Tea grows well under air temperatures in the range of 18-25 C (Carl 1972; Watson, 1986). A well-distributed rainfall of about 1,300-1,400 mm per year is generally considered adequate for the growth of tea in Sri Lanka. It is also reported that an annual rainfall of about 2,500-3,000 mm is optimum for tea cultivation (Fuch, 1989; Watson, 1986). There is a wide variation in temperature and rainfall in the different tea growing regions in Sri Lanka.

    Although the relationship between weather and tea yield has shown that increases in rainfall and temperature increase tea yield (Devanathan, 1975; Squire, 1990), recent observations have shown that at higher temperature regimes (>25-26 C), the yield components of tea (shoot population density, shoot weight, and shoot extension rate) tend to decrease with increasing temperatures:

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    where SW, SER, and T are the shoot dry weight (g/shoot), shoot extension rate (mm/week), and temperature (C), respectively. Low R 2 values were obtained because this experiment was conducted under field conditions where none of the environmental factors were controlled.

  • 90 M.A . WI JERATNE

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