Updated Basis Knowledge of Climate Change Summarized from the First part of Thailand’s Second Assessment Report on Climate Change

Recent evidence and key issues on climate change in Thailand have been presented in the first part of Thailand’s Second Assessment Report on Climate Change (2nd TRAC). The report highlights key findings including 1) a significant country-wide warming of 1.30 oC over the past 48 years (1970-2017); b) significant changes in rainfall patterns at smaller spatial and finer temporal scales; c) significant changes in temperature and rainfall extreme events over the last four-five decades; d) a significant decrease in frequency of tropical cyclones entering Thailand; e) significant rise in sea level in the seas around Thailand at higher rates than the global average; and f) significant projected increases in temperature and rainfall in Thailand by 2100. The first part of the 2nd TARC provides a comprehensive and updated analysis of climate change impacts in Thailand that can be used as an authoritative reference for building understanding and awareness, as well as for designing adaptation and mitigation strategies. Moreover, it can serve as a repository for scientific information to support further research related to impact, adaptation and vulnerability to climate change. Regular assessment of national climate change impacts is essential to informing national policy and to allow policymakers to assess priorities and set meaningful targets in line with the country’s international obligations under the Climate Change Agreement

ADELIE - Antarctic Drifter Experiment: Links to Isobaths and Ecosystems

The goal of the ADELIE research project is to map, for the first time, the near surface currents around the tip of the Antarctic Peninsula and to determine the role of these currents in the retention or dispersion of krill. Specifically, we will test the hypothesis that pathways to the west near the continent link current systems on the western and eastern sides of the the Peninsula. The influence of bathymetry controlling the splitting and steering of these frontal jets will also be studied. Data for the ADELIE project was collected during cruise JR158. We seek to resolve two important features of the current system around the margin of Antarctica, the Antarctic Slope Front and the Antarctic Coastal Current (see schematic in Figure 1). These currents both flow westward around the continent and are important for the transport of krill, for preconditioning the shelf waters, for the formation of Antarctic Bottom Water, and for supplying waters beneath ice shelves thus melting the underside of the ice shelf. The Antarctic Slope Front defines the boundary between cold, fresh waters filling the Antarctic continental shelf, and the warmer, more saline waters further offshore and is identified by a strong horizontal gradient in temperature and salinity. The Antarctic Coastal Current is a fast, shallow flow over the continental shelf often associated with the front of the ice shelf. The Coastal Current and the Slope Front may merge where the shelf is narrow, but over broad regions of the continental shelf the flows split into two distinct systems. The study area for JR158 is from the tip of the Antarctic Peninsula across the continental shelf and slope to the east and into the deep Weddell Sea (Figure 2). A CTD and Lowered ADCP section were conducted along this transect moving from east to west. This transect was selected to complement the western end of the WOCE SR4 time series, repeated annually by Eberhard Fahrbach and colleagues at the Alfred Wegener Institut (AWI) during the 1990’s. Due to the complexity of the topography in this region, Eulerian measurements at one site are not necessarily representative of the current system a short distance away. Therefore we also deployed surface drifters and Lagrangian floats as a means of tracking the currents. While surface drifters have been successfully released near the Antarctic continent during previous cruises, these drifters provide the first Lagrangian measurements of the current system on the eastern side of the Antarctic Peninsula. New instruments were also tested during JR158 including a microstructure profiler and a dissolved gas mass spectrometer. The microstructure profiler, which is used to resolve smallscale diapycnal mixing, will be used extensively during a mixing study near Kerguelen Island in 2008. The mass spectrometer measures dissolved oxygen/argon ratios that allow estimates of net community production over larger spatial scale with high temporal resolution

ADELIE - Antarctic Drifter Experiment: Links to Isobaths and Ecosystems

The goal of the ADELIE research project is to map, for the first time, the near surface currents around the tip of the Antarctic Peninsula and to determine the role of these currents in the retention or dispersion of krill. Specifically, we will test the hypothesis that pathways to the west near the continent link current systems on the western and eastern sides of the the Peninsula. The influence of bathymetry controlling the splitting and steering of these frontal jets will also be studied. Data for the ADELIE project was collected during cruise JR158. We seek to resolve two important features of the current system around the margin of Antarctica, the Antarctic Slope Front and the Antarctic Coastal Current (see schematic in Figure 1). These currents both flow westward around the continent and are important for the transport of krill, for preconditioning the shelf waters, for the formation of Antarctic Bottom Water, and for supplying waters beneath ice shelves thus melting the underside of the ice shelf. The Antarctic Slope Front defines the boundary between cold, fresh waters filling the Antarctic continental shelf, and the warmer, more saline waters further offshore and is identified by a strong horizontal gradient in temperature and salinity. The Antarctic Coastal Current is a fast, shallow flow over the continental shelf often associated with the front of the ice shelf. The Coastal Current and the Slope Front may merge where the shelf is narrow, but over broad regions of the continental shelf the flows split into two distinct systems. The study area for JR158 is from the tip of the Antarctic Peninsula across the continental shelf and slope to the east and into the deep Weddell Sea (Figure 2). A CTD and Lowered ADCP section were conducted along this transect moving from east to west. This transect was selected to complement the western end of the WOCE SR4 time series, repeated annually by Eberhard Fahrbach and colleagues at the Alfred Wegener Institut (AWI) during the 1990’s. Due to the complexity of the topography in this region, Eulerian measurements at one site are not necessarily representative of the current system a short distance away. Therefore we also deployed surface drifters and Lagrangian floats as a means of tracking the currents. While surface drifters have been successfully released near the Antarctic continent during previous cruises, these drifters provide the first Lagrangian measurements of the current system on the eastern side of the Antarctic Peninsula. New instruments were also tested during JR158 including a microstructure profiler and a dissolved gas mass spectrometer. The microstructure profiler, which is used to resolve smallscale diapycnal mixing, will be used extensively during a mixing study near Kerguelen Island in 2008. The mass spectrometer measures dissolved oxygen/argon ratios that allow estimates of net community production over larger spatial scale with high temporal resolution

Ocean temperature and salinity components of the Madden-Julian oscillation observed by Argo floats

New diagnostics of the Madden-Julian Oscillation (MJO) cycle in ocean temperature and, for the first time, salinity are presented. The MJO composites are based on 4 years of gridded Argo float data from 2003 to 2006, and extend from the surface to 1,400 m depth in the tropical Indian and Pacific Oceans. The MJO surface salinity anomalies are consistent with precipitation minus evaporation fluxes in the Indian Ocean, and with anomalous zonal advection in the Pacific. The Argo sea surface temperature and thermocline depth anomalies are consistent with previous studies using other data sets. The near-surface density changes due to salinity are comparable to, and partially offset, those due to temperature, emphasising the importance of including salinity as well as temperature changes in mixed-layer modelling of tropical intraseasonal processes. The MJO-forced equatorial Kelvin wave that propagates along the thermocline in the Pacific extends down into the deep ocean, to at least 1,400 m. Coherent, statistically significant, MJO temperature and salinity anomalies are also present in the deep Indian Ocean

Future changes in annual precipitation extremes over Southeast Asia under global warming of 2°C

THIS ARTICLE PROVIDES detailed information on projected changes in annual precipitation extremes over Southeast Asia under global warming of 2°C based on the multi-model simulations of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment Southeast Asia (SEACLID/CORDEX-SEA). Four indices of extreme precipitation are considered: annual total precipitation (PRCPTOT), consecutive dry days (CDD), frequency of rainfall exceeding 50 mm/day (R50mm), and intensity of extreme precipitation (RX1day). The ensemble mean of 10 simulations showed reasonable performance in simulating observed characteristics of extreme precipitation during the historical period of 1986–2005. The year 2041 was taken as the year when global mean temperature reaches 2°C above pre-industrial levels under unmitigated climate change scenario based on Karmalkar and Bradley (2017). Results indicate that the most prominent changes during the period of 2031–2051 were largely significant. Robust increases in CDD imply impending drier conditions over Indonesia, while increases in RX1day suggest more intense rainfall events over most of Indochina under 2°C global warming scenario. Furthermore, northern Myanmar is projected to experience increases in CDD, R50mm and RX1day, suggesting that the area may face more serious repercussions than other areas in Southeast Asia

Climatology and Spatio-Temporal Variability of Wintertime Total and Extreme Rainfall in Thailand during 1970-2012

This study aims at examining wintertime (December-January-February; DJF) climatology and spatio-temporal variability of Thailand’s total and extreme rainfall during 1970-2012. Analysis showed that the area along the Gulf of Thailand’s eastern coast not only received much amount of rainfall but also underwent great extremes and variances during the northeast monsoon (NEM) winters. Empirical Orthogonal Function (EOF) analysis similarly revealed that the leading mode of each DJF total or extreme rainfall index was marked by maximum loadings concentrated at the stations located at the exposed area of the NEM flow. Correlation analysis indicated that the leading EOF mode of DJF total and extreme indices in Thailand tended to be higher (lower) than normal during strong (weak) East Asian Winter Monsoon (EAWM). On longer timescales, the recent decadal change observed in the leading EOF mode of all rainfall indices has been coincident with re-amplification of the EAWM taken place since the early/mid 2000. The leading EOF mode of DJF total and extreme rainfall indices in Thailand also exhibited strong correlations with the tropical-subtropical Pacific Ocean surface temperatures. It was characterized as the Pacific Decadal Oscillation (PDO)/El Niño Southern Oscillation (ENSO)-related boomerang-shaped spatial patterns, resembling the typical mature phases of the La Niña event and the PDO cool epoch. Based on our analysis, it is reasonable to believe that the anomalies of the NEM and other key EAWM-related circulations are likely to be the possible causes of DJF total and extreme rainfall variations in Thailand. In addition, the ENSO and PDO as the primary global atmospheric external forcing are likely to exert their influence on wintertime Thailand’s climate via modulating the EAWM/NEM-related circulations anomalies

Deep ocean impact of a Madden-Julian oscillation observed by Argo floats

Using the new Argo array of profiling floats that gives unprecedented space-time coverage of the upper 2000 meters of the global ocean, we present definitive evidence of a deep tropical ocean component of the Madden-Julian Oscillation (MJO). The surface wind stress anomalies associated with the MJO force eastward-propagating oceanic equatorial Kelvin waves that extend downward to 1500 meters. The amplitude of the deep ocean anomalies is up to 6 times the amplitude of the observed annual cycle. This deep ocean sink of energy input from the wind is potentially important for understanding phenomena such as El Nino-Southern Oscillation and for interpreting deep ocean measurements made from ships

Climatological Characterization of Tropical Cyclones Detected in the Regional Climate Simulations Over the CORDEX-SEA Domain

In this study, a subset of the downscaled simulations of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment—Southeast Asia (SEACLID/CORDEX-SEA) was analysed to examine the representation of tropical cyclone (TC) climatology over Southeast Asia, in terms of pattern, intensity, frequency, and lifetime. A modified vortex tracking algorithm is used to detect TCs over the SEACLID/CORDEX-SEA domain in the historical simulations from 1986 to 2005. Sensitivity tests for the detection method criteria, including vorticity, outer core wind strength, sea level pressure anomaly, and temperature anomaly at 300, 500, 700, and 850 hPa, were conducted to determine the optimum threshold configuration for each SEACLID/CORDEX-SEA simulation used in the study. Comparison with the best track data of the Joint Typhoon Warning Center showed that model simulations underestimated the total number of TCs east of the Philippines for the 1986–2005 period but captured the annual cycle of the total number of TCs. This underestimation of TCs is possibly due to the domain used, which does not extend further east to cover most of the TC genesis area in the Western North Pacific. The structure of a typical TC from the regional climate model simulation is comparable to observed TC structure. However, results indicate that the resolution of the simulations is still not sufficient to capture the fine details of the observed TC structure, which could explain in part the lower intensification rate of TCs in the model output

Sensitivity of Southeast Asia rainfall simulations to cumulus and air-sea flux parameterizations in RegCM4

We investigated the performance of RegCM4 in simulating rainfall over Southeast Asia with different combinations of deep-convection and air-sea flux parameterization schemes. Four different gridded rainfall datasets were used for the model assessment. In general, the simulations produced dry biases over the equatorial region and slightly wet biases over mainland Indo-China, except those experiments with the MIT Emanuel cumulus schemes, in which large positive rainfall biases were simulated. However, simulations with the MIT schemes were generally better at reproducing annual rainfall variations. The simulations were not sensitive to the treatment of air-sea fluxes. While the simulations generally produced the rainfall climatology well, all simulations showed stronger inter-annual variability compared to observations. Nevertheless, the time evolution of the inter-annual variations was well reproduced, particularly over the eastern Maritime Continent. Over mainland Southeast Asia, all simulations produced unrealistic rainfall anomaly responses to surface temperature. The lack of summer air-sea interactions in the model resulted in enhanced oceanic forcing over the regions, leading to positive rainfall anomalies during years with warm ocean temperature anomalies. This shortcoming in turn caused much stronger atmospheric forcing on the land surface processes compared to that of the observation. A robust score-ranking system was designed to rank the simulations according to their performance in reproducing different aspects of rainfall characteristics. The results suggest that the simulation with the MIT Emanuel convective scheme and the BATS1e air-sea flux scheme performs better overall compared to the rest of the simulations

Potential Influence of Sea Surface Temperature Representation in Climate Model Simulations Over CORDEX-SEA Domain

Regional climate simulations from the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment – Southeast Asia (SEA) indicated model biases in temperature and rainfall over SEA. Given the influence of sea surface temperature (SST) variability on SEA climate, this study examines SST representation in climate models to investigate its potential contribution to the resulting model biases over the Philippines. Observed SST over SEA is first characterized by its spatial patterns and temporal variability. An analysis of the SST representation over SEA and its potential influence on modelled climate over the Philippines in Coupled Model Intercomparison Project Phase 5 (CMIP5) global climate models (GCMs) is then conducted, followed by an assessment of the potential influence of SST representation in CMIP5 GCMs on downscaled regional climate output. Our results show that GCMs with well represented SSTs (i.e., low bias, well captured variability, and pattern) can produce climate simulations well over the Philippines. Whether or not the GCMs with poor SST representation can perform well is inconclusive. During boreal winter (summer), climate variables with high (low) spatial correlation with model SST get poor (better) spatial correlation with observed climate. Over west of the Philippines, where model SST seasonal variability is captured well, models also adequately simulate climate variables. Results suggest that the negative temperature biases, and positive precipitation and wind speed biases, in both GCMs and downscaled simulations, are associated with negative model SST biases. These findings give a better understanding on how SST potentially influences modelled climatology over the Philippines