THE ZONING AND CALCULATION OF AREAS ENDURED THE EFFECTS OF CLIMATE CHANGE IN THE LOWER MEKONG RIVER DELTA

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1 THE ZONING AND CALCULATION OF AREAS ENDURED THE EFFECTS OF CLIMATE CHANGE IN THE LOWER MEKONG RIVER DELTA Abstract The Lower Mekong River Delta (LMRD) are most affected by climate change which causes droughts, water shortages during the dry season (due to increase in air temperature, water demand in agriculture, hydropower water upstream of the Mekong River), flooding and salinity (floods, sea level rise). The determination and calculation of the area subject to these effects required for building an effective response plan. The report presents a method to evaluate effects of climate change on rice production through four factors: rice yield, flooded area, possibility of drought, and the boundaries saltwater intrusion. In the study, the Mekong Delta are classified into 6 sub-region. The calculation models of the study includes a Decision Support System for Agro-technology Transfer - DSSAT model, MIKE and ArcView software. Results of this study are rate of decrease in rice production and a zoning map of the effects of drought, flooding and salinity. I. Introduction In the Lower Mekong River Delta (LMRD), when climate change, the average sea water level will rise, especially in peak tidal water level will make the plain areas in the LMRD flooded and salinity boundary will be pushed deeper into inland. A significant portion of agricultural land in the coastal areas would be inundated by sea level rise (SLR). A consequence of drought is water shortage. In order to develop properly an eco-agriculture structure and ensure national food security, forecast information of yield of rice production for each region and each province is indispensable. It is more necessary to forecast the rice yield in the context of fluctuated weather. The aim of this study is to research impacts of climate change on rice production under the climate change scenarios 2020, 2050, and In this study, LMRD is divided into six subregions: West of Hau River, Long Xuyen Quadrangle, Between of Tien-Hau River, Dong Thap Muoi (Plain of Reeds), East Coast, Ca Mau Peninsula. II. Approach 1. Simulation of rice crop yield in the agro-ecological sub-region To simulate rice yield in the sub-region, the study have conducted investigations and surveys of rice cultivation at 10 sampling locations in the six sub-regions which represented for typical rice-growing areas. The weather elements are based on data series (from 1989 to 2009) from meteorological stations in the six sub-regions. Required data for the model comprise of the maximum air temperature, the minimum air temperature, precipitation and solar radiation a day. The data series is used to simulate yield as base value compared to rice yield in climate change scenarios

2 DSSAT Model simulates yield and seasonal comparison with actual performance. Rice yield simulation on the basis of the elements to make rice yields as cultivation techniques, irrigation regimes, fertilizer, seed, weather, season, land and soil...[3]. 2. Drought index calculation For the frequency of droughts, the study applied the Standardized Precipitation Index SPI (McKee et al. 1995) [4], and just used term frequency of occurrence which was severe drought (SPI <-1.5). Different types of drought (SPI index of > -1.5) was not focused in the report. A simple term frequency is the ratio of the month SPI <-1.5 on the total number of months in the period 1979 to In this calculation, the meteorological data for the period , SPI of Ca Mau station represent for the Ca Mau Peninsula, SPI of Rach Gia station represents for the Long Xuyen Quadrangle, West of Hau River and the SPI of Can Tho station represents for Between Tien - Hau River, Dong Thap Muoi, East Coast. 3. Zoning of inundation area For zoning of inundation areas, study used data released from the project "Building a basic database of terrain hydrological information system for flood prevention and socio-economic development of the Cuu Long implemented by the National Remote Sensing Center. The criteria of selected floodplains in the LMRD include [2]: - The areas of lower elevation terrain 0.12 meter, 0.30 meter and 0.75 meter according to the B2 scenario for 2020, 2050 and The coastal area. Figure 1: Six sub-regions, survey locations in LMRD

3 - The area is associated with the surface of rivers, lakes and canals connecting to the sea. 4. Saltwater intrusion For salinity, the study applied MIKE model to calculate salinity intrusion. - The upstream boundary are water levels at stations of Tan Chau and Chau Doc, - The estuary boundarie are water levels at 8 stations of Cua Dai, Cua Tieu, Ba Lai, Ham Luong, Co Chien, Cung Hau, Dinh An and Tran De. Data verification are the stations of My Thuan, My Hoa, Nam Can, Ca Mau, Soc Trang (5 stations). The Sea Level Rise scenarios are the B2 scenario in 2020, 2050, 2100 at 8 stations above. III. Results 1. Rice yield Figure 2: Network and cross sction of LMRD hydraulic model To simulate effect of the rice yield caused by climate change in the future, it is based on the average emission scenarios (scenario B2 as recommended by the Ministry of Natural Resources and Environment [1]). Below are the B2 scenarios of the changes in temperature and rainfall in LMRD. Table 1: The change of the mean temperature ( C) and precipitation (%) in LMRD in B2 scenario. Elements Temperature ( o C) Timeline Months XII - II III - V VI - VIII

4 Precipitation (%) IX - XI XII-II III-V VI-VIII IX-XI (Source: MONRE. 2009) 0.0 % Mức giàm năng suất lúa mô phỏng theo kịch bản B2 giai đoạn 2020, 2050 và 2100 tại đồng bằng sông Cửu Long Hè Thu Đông Xuân Thu Đông Figure 3: The reduction in rice yield simulation of LMRD under climate change scenarios The rice yield in LMRD is simulated by DSSAT model in the timeline of 2020, 2050 and Details of the yield reduction for the 6 sub-regions are shown in the table below: Table 2: Decrease of rice yield (in kg/ha and %) in the sub-regions according to B2 scenarios 1) West of Hau River 2) Long Xuyen Quadrangle Timeline Average yield (kg/ha) Decreased level (%) ) Between Tien _ Hau River 4) Dong Thap Muoi (Plain of Reeds) Average Productio n (kg/ha)

5 Decreased level (%) ) East Coast 6) Ca Mau Peninsula Average Productio n (kg/ha) Decreased level (%) To 2020: rice yield reduces not much with average rate: 2-3% and the highest of 6.6%. Especially, in Ca Mau Peninsula sub-region, yield tends to increase 5-6%. To 2050: rice yield decreases on average 6-9% and the highest 15% compared to the base time. To 2100: the most decrease year for rice yield with the average 16-21% and the highest 30% compared to the base time. 2. Inundation areas For LMRD, the average sea level rises highly, especially in peak tidal water level, will cause flooding of lowland areas and deliver saltwater from sea to inland. Saltwater boundaries will enter further to inland. A significant portion of agricultural land in the coastal lowlands would be flooded by sea level rise. Table 3: Inundated rice area and percentage (%) by sea level rise Rice Inundated area Sub-region area cm cm cm (km 2 ) km 2 % km 2 % km 2 % Ca Mau Peninsula 6, % % % Between Tien-Hau River 2, % % % West of Hau River 3, % % % Long Xuyen Quadrangle 3, % % % East Coast 3, % % % Dong Thap Muoi (Plain of reeds) 3, % % % LMRD 22, % % %

6 Figure 4: Inundated area of LMRD in 2050 and 2100 Rice area is quite large with the proportion up to 60% areas of LMRD. It is supposed that rice area is permanently flooded. If, sea levels is 12 cm, 30cm, 75cm, the flooded rice area is 1.4%, 6% and 38%, respectively. 3. Saltwater intrusion Saline rice area is simulated by climate change impacts in the timeline as follows: 38% by 2020, 52.5% by 2050 and 83.2% by The saline area of whole LRMD are presented in Figure 5. Table 4: Rice area and area percentage of 4 salinity in the dry season Rice Saline area Sub-region area (km 2 ) cm cm cm km 2 % km 2 % km 2 % Ca Mau Peninsula % % % Between Tien-Hau River % % % West of Hau River % % % Long Xuyen Quadrangle % % % East Coast % % % Dong Thap Muoi (Plain of reeds) % % % LMRD area % % %

7 Figure 5: Salinity area of LMRD in 2020, 2050 If the salinity boundaries is 4, rice area in LMRD decreases as follows: - By 2020, rice area remains only 62-64% compared to today. - By 2050, rice area remains only 48-53% compared to today. - By 2100, rice area remains only 17-20% compared to today. 4. Drought index The drought also leads to decline of rice yields due to water shortage during rice growth period.in Ca Mau Peninsula, possibility of severe drought is 6.16%. Between the Tien - Hau River, Dong Thap Muoi, East Coast have possibility of severe drought of 6.46%. Regions such as the Long Xuyen Quadrangle, West of Hau River with possibility of severe drought is 4.49% 5. The combination of factors In 2020, in LMRD, there are 12 kinds of area endured from 1 to 3 effects of inundation, salinity and drought of 3 different frequencies. The area endured the effect of 6.46%- frequency drought is the largest with km 2 (near 34% of LMRD area). The second large area endured the effects of both the 6.16%-frequency drought and salinity intrusion with 9660 km 2 (over 25% of LMRD area). The areas endured 3 effects of inundation, salinity and drought of 3 different frequencies 4.49%, 6.16% and 6.46% respectively are 29 km 2, 180 km 2 and 229 km 2 (total occupied 1.15% of LMRD area).

8 Figure 6: Rice areas and the impact of flooding. salinity. drought in 2020 scenarios In 2050, the area endured only the effect of 6.46%- frequency drought still is the largest with km 2 (near 27% of LMRD area). The second large area endured the effects of both the 6.16%-frequency drought and salinity intrusion with 9507 km 2 (25% of LMRD area). The areas endured 3 effects of inundation, salinity and drought of 3 different frequencies 4.49%, 6.16% and 6.46% respectively are 426 km 2, 898 km 2 and 579 km 2 (total occupied 5.04% of LMRD area). In 2100, the area endured the effects of both 6.46%-frequency drought and salinity intrusion is the largest with km 2 (near 27% of LMRD area). The second large area endured 3 effects of inundation, salinity and 6.16%-frequency drought is 5573 km 2 (near 15% of LMRD area). The areas endured 3 effects of inundation, salinity and drought of 3 different frequencies 4.49%, 6.16% and 6.46% respectively are 3644 km 2, 5573 km 2 and 2848 km 2 (total occupied 31.92% of LMRD area). Table 6: The effects of drought, inundation and salinity intrusion in LMRD in 2100 Effects Area (km 2 ) Percentage to LMRD area (%) Drought of 4.49% frequency Drought of 4.49% frequency and innundation Drought of 4.49% frequency and salinity 4 1, Drought of 4.49% frequency,salinity 4, innundation 1, Drought of 6.16% frequency Drought of 6.16% frequency and innundation Drought of 6.16% frequency and salinity 4 2, Drought of 6.16% frequency,salinity 4, innundation 1, Drought of 6.46% frequency 1, Drought of 6.46% frequency and innundation

9 Drought of 6.46% frequency and salinity 4 3, Drought of 6.46% frequency,salinity 4, innundation 1, Drought of 4.49% frequency in rice area Drought of 4.49% frequency and inundation in rice area Drought of 4.49% frequency and salinity 4 in rice area 2, Drought of 4.49% frequency,salinity 4, inundation in rice area 2, Drought of 6.16% frequency in rice area Drought of 6.16% frequency and inundation in rice area Drought of 6.16% frequency and salinity 4 in rice area 2, Drought of 6.16% frequency,salinity 4, inundation in rice area 3, Drought of 6.46% frequency in rice area 1, Drought of 6.46% frequency and inundation in rice area Drought of 6.46% frequency and salinity 4 in rice area 6, Drought of 6.46% frequency,salinity 4, inundation in rice area 1, IV. Conclusion LMRD 37, Results of the study show that the effects of climate change on rice yield from weather, salinity, sea level rise and drought factors are to reduce rice production and the risk of narrowing the area of rice cultivation in the LMRD. Rice yield is decreased significantly by climate change impacts in different periods. Rice yield can decrease 6% by2020, 15% by 2050 and even 30% by The area of agricultural land, especially rice cultivated land is decreasing by sea level rise, salinity intrusion besides the reasons of urbanization and industrialization. In summary, results provided a scientific basis for agricultural development strategies in general and rice production in particular so that ensure national food security and give direction for adaptation measures in the context of climate change. Acknowledgement All information of this report is quoted from the comprehensive report of our research at ministerial level named Assessment of climate change impacts on rice production in Mekong River Delta. Reference 1. MONRE. Climate change. sea level rise scenarios for Vietnam Ha Noi. June. 6/2009

10 2. Bao Thanh. Bui Chi Nam. Assess damage caused by rising sea levels in coastal Lower Mekong River Delta. Journal of Hydrometeorology. No National centrre for Hydrometeorology forecasting (In Vietnamese) 3. ICASA. DSSAT V4 volume 1-4. University of Hawaii McKee. T.B.; N.J. Doesken; and J. Kleist The relationship of drought frequency and duration to time scales. Eighth Conference on Applied Climatology. January Anaheim. California. pp Paper Reference No.: PN-53 Title of the paper : THE ZONING AND CALCULATION OF AREAS ENDURED THE EFFECTS OF CLIMATE CHANGE IN THE LOWER MEKONG RIVER DELTA Name of the Presenter : Bao Thanh

11 Author (s) Affiliation : Nguyen Thi Phuong, Bui Chi Nam, Tran Tuan Hoang Mailing Address : 19 Nguyen Thi Minh Khai street, District 1, Ho Chi Minh city, Vietnam Address : bao_thanh1956@yahoo.com Telephone number (s): Fax number (s) : Brief Biography: Thanh BAO graduated from the University of Ho Chi Minh City, Vietnam in 1978 with B.S. degrees in oceanographic physics. He has his PhD s in geohydrodynamics at the Institute of Meteorology and Hydrology (IMHEN) in Hanoi, Vietnam. He worked in governmental institutions of Vietnam HydroMeteorological Services (HMS) and Ministry of Natural Resources and Environment (MONRE) for 34 years. During this period he participated in and headed many national, ministerial and provincial research projects and also many international cooperation projects including Intergovernmental Oceanographic Commission (IOC), IOC-WESTPAC, the Korean International Cooperation Agency (KOICA), JICA, SIDA, START, Germany Cottbus University of Technology, Finland Geology Surveys, etc. At present, he is the Vice Director of Institute of Meteorology, Hydrology and Environment (IMHEN) and the Director of Sub-Institute of HydroMeteorology and Environment of South Vietnam in Ho Chi Minh City.