Change in Extreme Precipitation Over Indochina Under Climate Change From a Lagrangian Perspective of Water Vapor

The process of global warming has humidified the atmosphere and increased the occurrence of extreme-precipitation events over the Indochina Peninsula, which lies in the transition region from the South Asian monsoon to the East Asian monsoon. The annual occurrence number of days of extreme precipitation over the Indochina Peninsula exhibits a significant change in 2003, with an abnormally higher occurrence number during the period 2003–2015 than that during 1951–2002. The extreme precipitation and such decadal change are contributed by more moisture sources associated with an enhanced dipole circulation over the Indian Ocean, which could be linked to the Pacific Decadal Oscillation. The daily large-scale meteorological pattern directly associated with extreme precipitation is characterized by an enhanced dipole of the typical summer monsoon pattern, with a zonally elongated Mascarene high and a deepened monsoon trough from northern India to the South China Sea. Such an intensified dipole provides two major channels of water vapor: one along the low-level westerly jet over the Indian Ocean and the other along the gyre of monsoon trough over the South China Sea. Compared with that during the period 1951–2002, the dipole is enhanced from northern India to the Indian Ocean and weakened over the Indochina Peninsula during the period 2003–2015. Although the Lagrangian analysis shows that the trajectory of air masses is displaced southward to the Indian Ocean, the intensified low-level westerly jet increases the evaporation of water from the ocean and thus not only enhances the water channel over the Indian Ocean but also yields a parallel water channel over the Bay of Bengal. In contrast, in spite of the increased trajectory density of air masses over the South China Sea, the lingering of air mass suppresses the evaporation of water and thus provides a declined contribution to the extreme precipitation during 2003–2015.

Geographic isolation created distinct pelage characters in Finlayson’s squirrel on isolated island offshore of the Indochina Peninsula in Central Vietnam

We found distinct pelage characters in Finlayson’s squirrel (Callosciurus finlaysonii) population, which is endemic to Lao Island of the Cham Islands, located off the coast of central Vietnam. Among squirrels of the ‘C. erythraeus-finlaysonii complex’, which consists of all forms of C. erythraeus and C. finlaysonii, mitochondrial cytochrome-b sequences show that the Lao Island squirrel forms a cluster with C. finlaysonii with external characters of C. erythraeus flavimanus, defined previously as ‘C. finlaysonii morpha flavimanus’. Both squirrel forms, however, differed in pelage colour. This different colouration may have arisen from the effect of geographic isolation.

Future projection of extreme precipitation indices over the Indochina Peninsula and South China in CMIP6 models

A future projection of four extreme precipitation indices over the Indochina Peninsula and South China (INCSC) region with reference to the period 1958–2014 is conducted through the application of multimodel ensemble approach and rank-based weighting method. The weight of each model from phase 6 of the Coupled Model Intercomparison Project (CMIP6) is calculated depending on its historical simulation skill. Then, the weighted and unweighted ensembles are used for future projections. The results show that all four extreme precipitation indices are expected to increase over the INCSC region, both in the middle (2041–2060) and at the end (2081–2100) of the 21st century, under three Shared Socioeconomic Pathway (SSP) scenarios. The increases in total extreme precipitation (R95p), extreme precipitation days (R95d), and the fraction of total rainfall from events exceeding the extreme precipitation threshold (R95pT) in the Indochina Peninsula are more significant than those in South China. The occurrence of extreme rainfall events may become more frequent in the future over the INCSC region, since the probability that R95pT increases is larger than 0.7 in the whole INCSC region. A comparison between the weighted and unweighted ensemble means shows that the uncertainty over South China is almost always reduced after applying the weighted scheme to future probabilistic projection, while the reductions in uncertainty over the Indochina Peninsula may depend on SSPs. The more extreme precipitation over the INCSC region in the future may be related to the larger water vapor supply and the more unstable local atmospheric stratification.

A new subspecies of Finlayson’s squirrel from an isolated island offshore of the Indochina Peninsula in southern Vietnam

We describe a new subspecies of Finlayson’s squirrel (Callosciurus finlaysonii) from Hon Nghe Island in the Gulf of Thailand. This island is located off the coast of southern Vietnam. In addition, we discussed the phylogenetic relationships among C. finlaysonii subspecies distributed on the isolated islands in the Gulf of Thailand. The new subspecies (C. finlaysonii honnghensis), which is endemic to Hon Nghe Island, differs from other C. finlaysonii subspecies in pelage colouration. The mitochondrial cytochrome b sequences showed that this squirrel is closely related to C. finlaysonii albivexilli and C. finlaysonii frandseni, which are endemic to the Koh Kut and Koh Chang islands, respectively, suggesting that the three subspecies diverged approximately 30,000 years ago. After the last glacial maximum, many small islands were formed by the sea level rise in the Gulf of Thailand, which was a consequence of global warming. Following the continuous fragmentation of the Sunda Continent, each C. finlaysonii subspecies could have evolved in each geographically isolated island in this gulf. Thus, studying C. finlaysonii subspecies may be used to track the recent geological history of the Gulf of Thailand.

Phylogenetic relationships among Callosciurus squirrels in the Indochina Peninsula: phylogenetic position of C. pygerythrus from Myanmar

The phylogenetic relationships among seven Callosciurus species from the Indochina Peninsula, including the C. honkhoaiensis which is endemic to Hon Khoai Island, were studied using complete mitochondrial cytochrome b gene sequences (1140 bases). We primarily focused on the phylogenetic position of C. pygerythrus, which is distributed in the western part of the peninsula. We identified two main lineages: 1) C. caniceps, C. honkhoaiensis, C. inornatus, C. phayrei and C. pygerythrus, and 2) C. erythraeus and C. finlaysonii. Estimated divergence time between the two lineages was at the junction of the Zanclean and Piacenzian in the Pliocene. Within the first linage, the divergence time of sub-lineages corresponded to the Pliocene-Pleistocene boundary, although phylogenetic relationships were unclear. These two divergence times estimated in the present study correspond to episodes of global cooling, suggesting that climate may have contributed to the divergence of these Callosciurus squirrels.

A 10-Year Climatology of Mesoscale Convective Systems and Their Synoptic Circulations in the Southwest Mountain Area of China

Hourly blackbody temperature data from the warm seasons (May–September) of 2009–18 were used to detect mesoscale convective systems (MCSs) generated in the southwest mountain area (elevation ≥ 500 m) of China. A total of 3059 MCSs were grouped into four categories (C1, C2, C3, and C4) according to their generation positions using K-means clustering. Major characteristics of the four types of MCSs and their synoptic environmental conditions were investigated. The MCSs had a peak in July and a minimum in May, and usually lasted from 3 to 21 h. The C1 MCSs generated in the northeast of the Tibetan Plateau developed faster, were largest, and had a longer lifespan. The C2 and C4 MCSs had greater intensity and were initiated in the southeast of the Tibetan Plateau and the west of the Yungui Plateau, and near the Wuling and Xuefeng Mountains, respectively. The C3 MCSs initiated in the Qinling, Ta-pa, and Wushan Mountains were smallest. The C1 and C2 MCSs contributed more than 30% to total precipitation, which was more than the C3 and C4 MCSs (<25%), and the contribution rate of MCSs to short-duration heavy rainfall affected by local MCSs was over 60%. Composite synoptic circulations of the four types of MCSs showed several factors, including the locations and intensities of cyclones in the Bay of Bengal and high pressure in the Indochina Peninsula in the low-to-middle troposphere, and vortexes or southwesterly winds in the low-level troposphere, regulate the location and intensity of convection.