|Year of Publication||2015|
|Series Editor||ลิ่มสกุล อัศมน, แพงแก้ว วุฒิชัย|
Rubber (Hevea brasiliensis) is Thailand’s economically important crop which its growth and phenology depend strongly on climate. Fluctuations in climate conditions can therefore impact on rubber growth and production in different dimensions. The climatedriven impact is particularly important in southern Thailand where is the country’s largest rubber cultivation area while this region has been identified as exceptionally vulnerable to changes in climate. In this study, the impacts of climate variability and change on rubber production and possible climate-rubber linkages in southern Thailand were investigated in 7 provinces (Songkhla, Patthalung, Nakhon SriThammarat, Surat Thani, PhangNga, Krabi and Trang). The major research activities undertaken in this study included 1) examining available historical data to illustrate the linkages between climate conditions in southern Thailand and regional climate phenomena as well as the relationships with rubber production, 2) assessing the impacts of climate variability on annual development and production of rubber at selected pilot rubber plantation sites and 3) analyzing household-level rubber plantation damage data due to extreme flood and tropical storm events in Patthalung province.
The results reveal that regional climate phenomena such as the El Niño-Southern Oscillation (ENSO), the Asian monsoon systems and anthropogenic-driven climate change can induce climate anomalies in southern Thailand through ‘atmospheric teleconnection’. On an annual cycle, the climate anomalies play a crucial role as one of mechanisms affecting annual variations in rubber production. However, the climate-rubber linkage apparent on this time scale appears to be a complex relationship which is often hidden its pattern under the dominant variations of other non-climate factors. By comparison, this climate-rubber relationship was characterized by opposite patterns between the Andaman Sea and the Gulf of Thailand, reflecting different responses of rubber to annual variations of climate conditions especially those associated with the Asian monsoon systems. The results also illustrated that interannual variations in rubber production in southern Thailand correlated significantly with the ENSO and some extreme rainfall indices. In summary, rubber production tended to be higher than normal in the periods where the El Niño events took place. This may be due to lower rainfall amounts, humidity and wind speed during the El Niño events in combination with the increased number of tapped days because of lower number of rainy days and rainfall intensity. In contrast, rubber production showed decreased tendency during the La Niña event due to increases in rainy days, rainfall amounts and air moisture.
An examination of the data collected at the selected pilot rubber plantation sites also showed some relationships between climate factors and rubber growth and production, consistent with the above-mentioned results. It was evidenced that the number of tapped days both the Andaman Sea and the Gulf of Thailand positively correlated with the number of dry days. This indicates that the number of tapped days and rubber production in southern Thailand generally declined in the months when there were higher than normal of the number of rainy days, often corresponding to the La Niña events or the strengthening of the Northeast and Southwest monsoons. In addition, rubber production especially in the Gulf of Thailand had positive correlation with the variations in E-P (Evaporation-Precipitation) balance. That is to say, rubber production tended to be higher in the months with positive E-P or the period when rainfall amounts were less than evaporation which corresponds to the dry phase (El Niño event) of the ENSO or the weakening of the Asian monsoon. Soil moisture data also showed increased percentages of moisture especially in the Gulf of Thailand, as a direct result of frequent heavy rainfall events and inundations. The findings from the pilot sites were consistent with the examination of secondary data showing that EP in both sites of southern Thailand exhibited decreasing trends (surplus accumulation of rainfall amounts than evaporation) since 1982. Fluctuations in climate conditions in the forms of E-P, consecutive rainy days, heavy rainfall events and unusual rainfall events in summer months also exert their indirect and accumulated influences on some characteristics related to phenology and annual development of rubber. The impacts on rubber phenology observed in the pilot sites included the abnormal leaf defoliation due to heavy rainfall events occurred during summer months and the anomalies of air moisture and evaporation causing the inflection of powdery mildew disease. This inflection led to twice defoliation, resulting in poor refoliation of rubber trees. Lower quality of latex in terms of dry rubber content (DRC) and reduced effectiveness of rubber tree photosynthesis are another phonological-related impacts observed in the pilot sites.
In addition, extreme-induced disasters from tropical storms and heavy rainfall events which are common consequences of climate change had direct damages by toppling rubber trees and inundation. Analysis of household-level rubber plantation data compiled in Patthalung province showed that just only one short-lived extreme flooding event which occurred in November 2010 caused widespread and severe damages of rubber plantations. The estimated economic damages in terms of monetary compensation to farmers were at least one thundered million baths.
This study provides some evidence, to a greater extent, showing that rubber is one of climate-sensitive crops. However, several issues remain unclear due primarily to a limitation of rubber data which series are quite short and digital forms are not readily available. The complex and non-linear connections between climate and rubber similar to other physical-biological linkages that need advanced multivariate statistics to encode such interactions are another fact to lower our better understanding. Therefore, further research to improve the current knowledge in particularly important issues including 1) area-based process study, 2) future impact projection, 3) high-quality data base compilation as well as 4) an extension of similar study to the areas which rubber cultivations have been fast growing is needed to be continued.
|Alternate Title||Climate Variability and Change in Southern Thailand Affecting Rubber Production|