Monday, 17 September 2012
Impact of Climate Change on Agriculture in Sri Lanka and Possible Response Strategies
By B.V.R. Punyawardena
In spite of the technological advances made on improved crop management, irrigation, plant protection and fertilization; weather and climate remain the key factors of agricultural productivity in any country. Farming systems and agronomic practices in most agricultural regions of Sri Lanka have evolved in close harmony with the prevailing conditions of the respective climatic regions of the island. However, it has been made evident during recent decades that the heritage of farming experiences and accumulated weather lore of centuries are no longer useful in the process of agricultural planning at any level. The Climate of the island has undergone a change to such an extent that the expected rainfall does not come at the correct time and severely handicapping farmers during growing season. Variability of both summer and winter monsoon rains and rains of convectional origin has increased significantly during recent decades (Table 1). As a result, both extremes, i.e., water scarcity and excess water have become a recurrent problem faced by crop production in Sri Lanka. Meanwhile, increasing ambient temperature has also resulted in several direct and indirect negative impacts on crop growth. However, intensively managed livestock sector of the country is not so vulnerable to climate change compared to the food crops sector. But, the situation is obviously different for extensively managed livestock sector where it is purely dependent on the rain-fed pastoral systems. Meanwhile, additional pressure coming from ever-increasing population, poor terms of trade, weak infrastructure, lack of access to modern technology, and information and civil disturbances will restrict the options available for people to cope with the negative consequences of climate change (Punyawardena, 2002).
Irrespective of the sectoral characteristics, the impact of climate change on any sector depends on how and what intensity the rainfall regime in a given area is variable along with the increasing environmental temperature of the same area. In addition, effects of climate change will be felt in the coastal region when sea levels rise as a result of an enhanced temperature regime - thereby affecting agriculture in low lying areas. This and other impacts of increasing temperature demand our special attention as the average temperature of the country has been rising annually at a rate of 0.01-0.0360C (Fernando and Chandrapala, 1995).
Impact due to Changes on Rainfall Regime
It is a well known fact that annual rainfall in Sri Lanka has shown a neither significant increasing/decreasing trend except in a few locations. However, variability of annual and seasonal rainfall have increased during recent decades especially with respect to the Northeast Monsoon which is the life blood of the Maha Season, the major cultivation season of Sri Lanka (Table 1). It is also true for the first inter-monsoon rains, especially during April which is the major rain producing month of the season in the Dry and Inter-mediate Zones. Those two Zones are considered to be the major food producing Zones of the country
Increased occurrence of extreme rainfall events due to climate change, droughts and floods, has become a common feature of the climate of Sri Lanka during recent decades. Under such situations, crop losses due to decreased soil moisture and excess water, both in terms of quality and quantity are inevitable. Given the physical conditions of most of the great soil groups that are being used for agricultural activities in Sri Lanka, even a small negative departure of expected rainfall is likely to cause a several-fold decrease in ground water replenishment. It will be extremely detrimental to the intensive agricultural production systems that are being practiced on sandy soils (Regosol) with lift irrigation systems (i.e., Kalpitiya and Jaffna Peninsula). Moreover, increased occurrence of positive rainfall anomalies is likely to cause severe damages to existing irrigation infrastructures and thus, limiting the water availability for crop production that is under irrigation.
Fruit bearing seasons of country’s major tree fruit crops are also likely to be affected due to irregularities in rainfall pattern under a changing climate. For example, Rambutan trees in the Wet zone requires 3-4 weeks of dry spell in and around February for flower development and primordial initiation, to give the harvest in June. However, sudden occurrence of rains in February deprives that prerequisite, resulting in no flowering in March. Such situations have become a common feature in the climate of the Wet Zone during recent times.
Impact due to Increased Ambient Temperature
Being a tropical island with uniformly high temperature regime, most of the cultivated crops in Sri Lanka operate at a near maximum of the optimum temperature range of respective crops. Thus, crop injuries due to high temperatures are inevitable in Sri Lankan agriculture under a changing climate. This is of particular importance for the country’s major staple food, rice. It is a well established fact that high temperature injuries in rice are inevitable if the plant is exposed to an ambient temperature that exceeds 350 C for 60-90 minutes at anthesis stage (flowering). It used to be a rare event to experience such an environmental temperature regime in major rice growing regions of the country, however recent agro-meteorological observations have confirmed that the frequency of such temperature occurrences have increased significantly in both the Dry and Intermediate Zones, especially during Yala season - resulting in a high rate of un-filled grains due to increased spikelet sterility. The high temperature regime will also increase evapotranspiration losses leading to frequent soil moisture stress conditions in upland crops.
Decreased diurnal temperature regime at almost all locations of the country, especially due to the increasing night time minimum temperature, is likely to cause negative impacts on tube crop production in the country. This is especially true for potato cultivation as the existing environmental temperature regime is sub-optimal for the crop even in the Up country region where the crop is mainly concentrated. In addition, the quality of the harvested crops is also affected negatively due to reasons which can be attributed to climate change. Increased temperature, especially that of night time minimum temperature, tends to decrease the sugar translocations in harvestable fruits and increasing the sour taste in fruit crops. This will be true for crops like sugarcane as well, therefore decreasing its brix value. Meanwhile, fiber content of harvestable parts of crops is also likely to increase under increased temperature regime and thereby reducing their palatability.
Yield of almost all crops grown in the country would also be negatively affected due to increases in insect damages and infestation various pathogens such as bacteria, virus and fungi. Even though higher yield loss due to increased weed infestation is likely to occur with increasing temperature, recent studies have shown that no such trend has been observed under local conditions. However, it is too early to generalize that such threats would not occur in the future.
Apart from the direct impact of increased variability of rainfall and rise of ambient temperature, indirect effects of increased rainfall intensities are of special significance in terms of land degradation which has a significant bearing on the crop production in Sri Lanka. Increased temperatures are likely to enhance the local scale convection and thereby to form more cumulonimbus clouds giving rise to high intensive rains (>25 mm/hr). Such rains invariably wash off the fertile top soil of arable lands. It will lead to subsequent siltation and eutrophication of downstream reservoirs and any other surface water bodies. Moreover, increased temperature and frequent and negative rainfall anomalies are also likely to cause high evaporative demand of the atmosphere. This can cause stalinization of agricultural lands in semi-arid parts of the country. The same will lead to rapid drying up of tanks giving rise and an additional pressure to the water available for agriculture. This is of particular importance with country’s cascade of minor tanks found in the Dry and Intermediate Zones of Sri Lanka. These tanks posses a high surface/depth ratio and hence, are highly vulnerable for rapid drying up. This will exacerbate the impact of negative anomalies of rainfall on crop production in water limiting regions of the country.
Impacts due to Increased Sea Level
As an island, Sri Lanka is highly vulnerable to increases in sea level with varying degrees of sectoral impacts. It is highly probable that sea water intrusion to agricultural lands is inevitable as a result of the changing climate, which will lead to further reduction of land available for agriculture. Increased sea levels will also exacerbate coastal erosion, piling on additional pressure on the land available for agriculture, directly and indirectly. Also, it may reduce the quality of both drinking and irrigation water in coastal regions by disturbing the interface between fresh and brackish water. It is highly likely that sea level rise will disturb the Gyben-Herzberg lens of fresh water found underneath Regosol in coastal regions. These fresh water lenses provide the irrigation water for intensive agriculture in those regions.
Response Strategies to Minimize the Vulnerability
Being a developing country, the most appropriate response strategy for climate change is adaptation activities rather than mitigation exercises. However, that does not mean that mitigation measures should be abandoned altogether, instead, the situation calls for a combination of both of measures - as long as they do not curtail development goals. Following is an exhaustive list that may be adapted by different stakeholders within the sector to minimize their vulnerability to climate change. But, it should be kept in mind that some of these proposed strategies are not new to our farming community and that they are already in practice. However, there is a timely need for implementation in a coordinated and systematic manner. There may also be some opportunities to re-evaluate the existing methodologies and introduce new concepts applicable to agricultural enterprise to cope with the additional pressure that would arise due to climate change. However, it is the responsibility of implementing agency to make sure that revised or new adaptation responses would deliver the goods even if the climate change does not take place to the level of envisaged degree. They should also take necessary precautions to avoid costly involvements on account of climate change. Any strategy that makes substantial negative impact on the socio-economic development of the country should not be considered as a viable option to combat the negative impact of climate change.
Suggested Adaption Strategies – Technical
There are several technical adaptation strategies available to mitigate vulnerability. The promotion of micro irrigation, in the form of drips and sprinklers, for instance will put a minimal amount of water to maximum use, contemporary examples of this system are to be found in moisture sparse agricultural areas in California and the middle-east. Other water management methods include the harvesting of rain water, the repair and rehabilitation of irrigation tanks and canals, and re-use of drainage water.
Other methods include, upland annual crop cultivation in the Dry Zone to be transformed to perennial fruit crop cultivation with intensive irrigation management practices wherever possible; Crop recommendation based on the agro-ecological suitability; Promote on-farm soil and moisture conservation; use of tail water recovery pits for lift irrigation; implement a programme to improve the water use and conveyance efficiency; breeding for short age varieties and varieties that can withstand drought, high temperature, pest & diseases and salinity; use of long range weather forecasting mechanisms to aid agricultural planning; periodic revision of fertilizer recommendations and soil test based fertilizer application.
Suggested Adaption Strategies – Policy Reforms
There are policy measures that can be taken to ensure that appropriate conservation and coping mechanisms are adapted in to the mainstream agricultural development agenda. The implementation of the Soil Conservation Act of 1996 for instance, would be an excellent first step. In addition strict enforcement of the National Environmental Act and other related ordinances would make sure that resources are utilized in an appropriate manner than ensures longevity instead of short term gain. Adoption of proper national land use policy and easy credit schemes to reward conservation activities such as soil and moisture conservation; micro-irrigation; storage and processing and high quality seeds would help propagate responsible farming practices amongst the agricultural community.
In addition, large scale drainage improvement projects in the low country Wet Zone is absolutely essential to make sure that all arable lands will be put back into cultivation or any other meaningful use without wasting valuable natural resource base. The development of guidelines for rational use of ground water will create an impact in this regard as well. Most importantly however, an effective marketing strategy to get the messages of conservation and adaptation across needs to be developed to ensure the Sri Lankan agriculture sector’s response to climate change isn’t too little, too late.
Fernando, T.K. and L.Chandrapala, 1995. Climate Variability in Sri Lanka – A Study of Trends of Air Temperature, Rainfall and Thunder Activity. Proceedings of international symposium on climate and life in Asia-Pacific, April 10-13, 1995, Brunei.
Punyawardena, B.V.R., 2002, Climate Change and Food Security, Abstract of the paper presented at the seminar on “National Climate Change Public Awareness, Information and Outreach in Sri Lanka organized by the centre for Climate Change Studies, Department of Meteorology in collaboration with LIFE and TSU of IPCC working group 111. December 13-14, 2002. Hotel Galadari, Colombo, Sri Lanka.
The Author, Dr. B.V.R.Punyawardena is the Head / Climatology Division, Natural Resources Management Centre, Department of Agriculture, Sri Lanka.