PROJECTIONS FOR VIETNAM

Transcription

1 HIGH-RESOLUTION CLIMATE PROJECTIONS FOR VIETNAM REGIONAL SOUTH CENTRAL

2 KEY FINDINGS CURRENT TRENDS PROJECTED TRENDS THROUGHOUT THE 21 ST Annual temperature observations showed a significant trend of about.8 to.16 C increase per decade, while annual rainfall observations also showed some increases. Annual temperature is projected to increase by about 1.3 to 4.3 C by end-of-century. Little change in annual rainfall amounts is projected, although seasonal changes are apparent. Heatwaves are projected to become more frequent and longer. The number of hot days is projected to increase. Droughts are projected to be less frequent, but last longer. Less intense extreme rainfall is projected. The length and intensity of the southwest monsoon are projected to decrease significantly. Projections indicate that the number of tropical cyclones may decrease. Other studies have also suggested some increases in intensity. Sea levels are projected rise by about 1 to 4mm by mid-century, with further increase by end-of-century and beyond. ABOUT THIS PUBLICATION This Regional Summary has been developed as part of the High-resolution Climate Projections for Vietnam project funded by Australia s Agency for International Development (AusAID) in order to provide information and data for updating the official climate change and sea-level rise scenarios for Vietnam in 215. This brochure provides a summary of the key findings from this research for the South Central region. For a summary of findings for all of Vietnam see the Project Summary Report and for more detailed information on the scientific approach and results see the Technical Report (available in 214). All publications and climate projection information can be accessed on the project website:

3 CURRENT CLIMATE CLIMATE FEATURES 1 Annual average temperature: 25 to 27 C Maximum temperature: 4 to 42 C Minimum temperature: 8 to 13 C Annual average rainfall: 12 to 2mm Daily maximum rainfall: 3 to 5mm Rainfall season: Aug to Dec FIGURE 1. MAP OF VIETNAM WITH SOUTH CENTRAL REGION HIGHLIGHTED. The station trend analyses (below) are based upon all available data within the last 5 years ( ). ANNUAL TEMPERATURE HAS INCREASED Temperature in this region has significantly 2 increased by approximately.8 to.16 C per decade (Figure 2). Note that only the trend at the Phan Rang station is not significant. HOANG SA ISLANDS MINIMUM TEMPERATURE HAS INCREASED MORE THAN MAXIMUM TEMPERATURE While minimum daily temperature has increased significantly by up to approximately.36 C per decade, the change in maximum daily temperature is small and not significant for most parts of this region. MORE HOT DAYS AND NO CHANGES IN COLD NIGHTS The number of hot days 3 has increased significantly by up to 4 days per decade at two stations. The number of cold nights 4 at the northern stations remains unchanged. PHU QUOC ISLAND TRUONG SA ISLANDS ANNUAL RAINFALL HAS INCREASED Station observations for annual rainfall have shown mostly increases for this region of up to approximately 13% at the Phan Rang station in the south (Figure 3). Note that trends at Nha Trang (south) and Tra My (north) stations are not significant. CON DAO ISLAND EXTREME RAINFALL AMOUNTS HAVE INCREASED Annual maxima of 1-day and 5-day rainfall amounts and the number of very wet days have increased throughout this region. But only the increase in the number of very wet days, of up to 3 days per decade, is significant for all stations. 1 Nguyễn Đức Ngữ, Nguyễn Trọng Hiệu (24). Khí hậu và tài nguyên khí hậu, NXB Nông nghiệp. Hà Nội. 2 Statistical significance has been calculated using the Mann-Kendall test. 3 Hot days with temperatures above 35 C. 4 Cold nights with temperatures below 15 C. SOUTH CENTRAL 1

4 FIGURE 2. ANNUAL TEMPERATURE TRENDS BASED ON STATION OBSERVATIONS. TEMPERATURE CHANGES ARE INDICATED FOR EACH STATION IN C PER DECADE. RED CIRCLES REPRESENT AN INCREASING TREND AND BLUE CIRCLES, DECREASING. CIRCLES ARE FILLED WHERE THERE ARE STATISTICALLY SIGNIFICANT TRENDS 2. ELEVATION IS INDICATED BY THE COLOUR BAR TO THE RIGHT AND LIGHT BLUE LINES REPRESENT MAJOR RIVERS. FIGURE 3. ANNUAL RAINFALL TRENDS BASED ON STATION OBSERVATIONS. RAINFALL CHANGES ARE INDICATED FOR EACH STATION IN PERCENT CHANGE PER DECADE. RED CIRCLES REPRESENT A DECREASING TREND AND BLUE CIRCLES, INCREASING. CIRCLES ARE FILLED WHERE THERE ARE STATISTICALLY SIGNIFICANT TRENDS 2. ELEVATION IS INDICATED BY THE COLOUR BAR TO THE RIGHT AND LIGHT BLUE LINES REPRESENT MAJOR RIVERS. 16N.15 DANANG m N 9.94 DANANG m N.12 TRAMY.16 QUANGNGAI.1 BATO N 5.49 TRAMY 1.1 QUANGNGAI BATO N QUYNHON.12 14N QUYNHON N TUYHOA.12 13N N NHATRANG 12N NHATRANG.11 PHANRANG 13.3 PHANRANG 11N.12 PHANTHIET.8 11N PHANTHIET PHUQUY PHUQUY 1N 1N 9N 9N TRUONGSA TRUONGSA 8N 17E 18E 19E 11E 111E 112E 113E 8N 17E 18E 19E 11E 111E 112E 113E 2 HIGH-RESOLUTION CLIMATE PROJECTIONS FOR VIETNAM

5 FUTURE CLIMATE Regional and global models 5 are used to project changes in rainfall and temperature by mid-century ( ) and end-of-century (28 299) relative to the baseline period (198 2). TEMPERATURE INCREASES Projections from regional models for average temperature changes by mid-century and end-of-century are presented in Table 1. The warming is very clear, with an increase in annual temperature of about 1.2 to 2.5 C by mid-century and 2.4 to 4.3 C by end-ofcentury under the higher (RCP8.5) greenhouse gas scenario. Greatest warming is projected in the SWMS 6 (Jun Sep). Less warming is evident in the lower () greenhouse gas scenario. TABLE 1. OF TEMPERATURE CHANGES (IN C) ANNUALLY AND BY SEASON 6 FROM REGIONAL MODELS FOR THE LOWER () AND HIGHER (RCP8.5) GREENHOUSE GAS SCENARIOS BY MID- ( ) AND END-OF- (28 299). THE AMOUNT AND AGREEMENT OF CHANGE AMONGST MODELS ARE INDICATED BY SHADING. LOWER GREENHOUSE GAS SCENARIO () HIGHER GREENHOUSE GAS SCENARIO (RCP8.5) LOWER GREENHOUSE GAS SCENARIO () HIGHER GREENHOUSE GAS SCENARIO (RCP8.5) ANNUAL CHANGES NEMS DEC MAR SEASONAL CHANGES FIMS APR MAY SWMS JUN SEP SIMS OCT NOV +1. to to to to to to to to to to to to to to to to to to to to +4.3 Small increase Half or more projections show increases of less than 2 C Medium increase More than half of projections show increases of 2 to 4 C High increase Half or more projections show increases of greater than 4 C 5 These are global climate models from the Coupled Model Intercomparison Project Phase 5 that will be used in the Intergovernmental Panel on Climate Change s Fifth Assessment Report. 6 Given the influence of monsoons on Vietnam s climate, monsoon-based seasons have been used in these analyses: North East Monsoon Season (NEMS), First Inter-Monsoon Season (FIMS), South West Monsoon Season (SWMS) and Second Inter-Monsoon Season (SIMS). SOUTH CENTRAL 3

6 TEMPERATURE INCREASES Projections of changes over time by global models, and the range of changes by end-of-century for both global and regional models, are presented for temperature in Figure 4. Both global and regional models agree on large increases in temperature by end-of-century, with less warming in the lower () greenhouse gas scenario. However, projections by the regional models show slightly less warming in all seasons except for the SWMS (Jun-Sep). The varying amounts of temperature increase signify the need to consider both mid-range and extreme changes. FIGURE 4. REGIONALLY AVERAGED SEASONAL TEMPERATURE CHANGES: SERIES GRAPH OF PROJECTIONS BY GLOBAL CLIMATE MODELS () SHOWN ON THE LEFT, FOR HIGHER (RCP8.5) GREENHOUSE GAS SCENARIO. END-OF- OF PROJECTIONS BY GLOBAL CLIMATE MODELS () AND REGIONAL CLIMATE MODELS () SHOWN AS BARS, ON THE RIGHT, FOR BOTH LOWER () AND HIGHER (RCP8.5) SCENARIOS. FIRST INTER-MONSOON SEASON (APR MAY) TEMPERATURE ( C) (LOWER) RCP CHANGE IN TEMPERATURE ( C) COMPARED TO HISTORIC BASELINE PERIOD (198 2) SOUTH WEST MONSOON SEASON (JUN SEP) TEMPERATURE ( C) (LOWER) RCP CHANGE IN TEMPERATURE ( C) COMPARED TO HISTORIC BASELINE PERIOD (198 2) HIGH-RESOLUTION CLIMATE PROJECTIONS FOR VIETNAM

7 LEGEND: Middle (bold) line is is the the mid-point value (median) of of or or simulations from from multiple models over a a 2-year average Shaded area is is between the the upper and and lower ranges ranges (9th (9th and and 1th 1th percentiles) of of or or simulations from from multiple multiple models models over over a 2-year a 2-year average. average. This This represents the the potential potential range range of of projections in any in any given given 2-year 2-year period. period. SECOND INTER-MONSOON SEASON (OCT NOV) TEMPERATURE ( C) (LOWER) RCP CHANGE IN TEMPERATURE ( C) COMPARED TO HISTORIC BASELINE PERIOD (198 2) NORTH EAST MONSOON SEASON (DEC MAR) TEMPERATURE ( C) (LOWER) RCP CHANGE IN TEMPERATURE ( C) COMPARED TO HISTORIC BASELINE PERIOD (198 2) SOUTH CENTRAL 5

8 SOME SEASONAL CHANGES IN RAINFALL Similar to temperature, projections of seasonal rainfall changes over time by global models, and the range of changes by end-of-century for both global and regional models, are presented in Figure 5. The only season with slightly more consistent changes amongst all models is the NEMS (Dec Mar), which mostly shows increases by both global and regional models. These projections for rainfall show larger variations in the direction of change than were projected for temperature. This reinforces the need to consider both mid-range and extreme changes. FIGURE 5. REGIONALLY AVERAGED SEASONAL RAINFALL CHANGES: SERIES GRAPH OF PROJECTIONS BY GLOBAL CLIMATE MODELS () SHOWN ON THE LEFT, FOR HIGHER (RCP8.5) GREENHOUSE GAS SCENARIO. END-OF- OF PROJECTIONS BY GLOBAL CLIMATE MODELS () AND REGIONAL CLIMATE MODELS () SHOWN AS BARS, ON THE RIGHT, FOR BOTH LOWER () AND HIGHER (RCP8.5) SCENARIOS. FIRST INTER-MONSOON SEASON (APR MAY) RAINFALL (MM/MONTH) (LOWER) % CHANGE IN RAINFALL COMPARED TO HISTORIC BASELINE PERIOD (198 2) 6 RCP SOUTH WEST MONSOON SEASON (JUN SEP) RAINFALL (MM/MONTH) % CHANGE IN RAINFALL COMPARED TO HISTORIC BASELINE PERIOD (198 2) 15 (LOWER) RCP HIGH-RESOLUTION CLIMATE PROJECTIONS FOR VIETNAM

9 LEGEND: 1. Middle (bold) line is the mid-point value (median) of or simulations from multiple models over a 2-year average. 2. Shaded area is between the upper and lower ranges (9th and 1th percentiles) of or simulations from multiple models over a 2-year average. This represents the potential range of projections in any given 2-year period. SECOND-INTER MONSOON SEASON (OCT NOV) RAINFALL (MM/MONTH) (LOWER) RCP % CHANGE IN RAINFALL COMPARED TO HISTORIC BASELINE PERIOD (198 2) NORTH EAST MONSOON SEASON (DEC MAR) RAINFALL (MM/MONTH) (LOWER) RCP % CHANGE IN RAINFALL COMPARED TO HISTORIC BASELINE PERIOD (198 2) SOUTH CENTRAL 7

10 SOME SEASONAL CHANGES IN RAINFALL Projections from regional models for annual rainfall (Table 2) show large variations in both direction and amount of change. However, there is strong agreement on increases projected for the NEMS (Dec Mar) and the FIMS (Apr May) by mid-century and end-of-century. In addition, there is some agreement on projected decrease for the SWMS 6 (Jun Sep) by mid-century and end-ofcentury. TABLE 2. OF RAINFALL CHANGES (IN %) ANNUALLY AND BY SEASON 6 FROM REGIONAL MODELS FOR THE LOWER () AND HIGHER (RCP8.5) GREENHOUSE GAS SCENARIOS BY MID- ( ) AND END-OF- (28 299). THE LEVEL OF AGREEMENT IN CHANGE IS INDICATED BY SHADING. LOWER GREENHOUSE GAS SCENARIO () HIGHER GREENHOUSE GAS SCENARIO (RCP8.5) LOWER GREENHOUSE GAS SCENARIO () HIGHER GREENHOUSE GAS SCENARIO (RCP8.5) ANNUAL CHANGES NEMS DEC MAR SEASONAL CHANGES FIMS APR MAY SWMS JUN SEP SIMS OCT NOV -8 to to to to to to to to to to to to to to to to to to to to +79 High agreement on decrease All projections show decrease Medium agreement on decrease More than half of the projections show decrease less than -1% Low agreement on change Projections do not agree or show little change Medium agreement on increase More than half of the projections show increase greater than +1% High agreement on increase All projections show increase 8 HIGH-RESOLUTION CLIMATE PROJECTIONS FOR VIETNAM

11 CLIMATE EXTREMES Projected changes throughout the 21 st century for a number of key climate extremes that affect this region are summarised below: MORE AND LONGER HEATWAVES The number and length of heatwaves (consecutive periods with hot conditions) are projected to increase by end-of-century. INCREASE IN THE NUMBER OF HOT DAYS The number of hot days (days with maximum temperatures above 35 C) is projected to increase by end-of-century. LESS INTENSE EXTREME RAINFALL Due to their rarity, changes in extreme rainfall events (annual maxima of 1-day and 5-day rainfall amounts) are not easy to project and are often associated with a large degree of uncertainty. Nevertheless, some regional projections show a tendency towards less intense extreme rainfall. FEWER DROUGHTS, BUT LONGER Some projections by regional models show that droughts (consecutive periods with a rainfall deficit) are expected to occur less often but may last longer. SOUTHWEST MONSOON WEAKENS Both the length and intensity of the southwest monsoon are expected to decrease significantly, based on some projections by regional models. By mid-century, the season length is projected to be reduced by about two weeks and rainfall is reduced by -4%. This trend continues until end-of-century. FEWER BUT POSSIBLY MORE INTENSE TROPICAL CYCLONES (TYPHOONS) Preliminary analysis of projections by regional models in this study suggests that the number of tropical cyclones may decrease in the East Vietnam Sea by mid-century. Other studies support this decreasing trend and suggest increases in intensity by end-of-century. SEA LEVELS WILL CONTINUE TO RISE The new projections indicate that the rate of sea-level rise during this century will be larger than the last. Sea levels rise approximately 1 to 4mm by mid-century with further increase by end-of-century and beyond. In addition, ground subsidence can occur in regions where there is ground water extraction or possible loss of sediment supply as rivers become more managed (i.e. more dams). These effects may be contributing to the substantially larger rates of relative sea-level rise at some locations.

12 CONTACT VIETNAM INSTITUTE OF METEOROLOGY, HYDROLOGY AND ENVIRONMENT WEB Assoc. Prof. Dr. Nguyen Van Thang PHONE For more information, please visit the project website: