Reconstructing fluvial dynamics is a fundamental requirement for understating the interaction between past environmental changes and human adaptation. This study focuses on the central part of the floodplain of the Nan River in northern Thailand that likely played a role in the catastrophic flood of 1818 CE, which damaged the ancient of Nan city and forced its relocation. We investigated nine sediment cores from the floodplain and from the eastern tributaries of the Nan River, to identify the potential source of floods in the past. By combining the analyses of sedimentary characteristics and provenance, the study reveals that the eastern tributaries were the dominant sediment source for most areas, with the Nan River only influencing areas close to its channel. According to optically stimulated luminescence dating, the highest sediment accumulation occurred during the eleventh to thirteenth centuries CE, coinciding with agricultural expansion and deforestation, suggesting increased erosion in the catchment of the tributaries. These findings challenge the assumption that the main Nan River has been the primary contributor to flooding catastrophes in the region and highlights the potential crucial role of smaller tributaries in similar settings in other parts of the globe.

Aerosols in Southeast Asia (SEA) are entangled with complex land-sea-atmosphere-human interactions, and it is difficult for scientists to understand their dynamic behaviors. This study aims to provide an insightful understanding of aerosols across SEA with respect to their radiative properties using several lines of evidence obtained from remote sensing instruments, including those from onboard Earth observation satellites (MODIS/Terra and MODIS/Aqua, CALIOP/CALIPSO) and from ground-based observation (AERONET). The findings, obtained from cluster analysis of aerosol optical properties, showed seven aerosol types which were dominant across the country, exhibiting diverse radiative forcing potentials. The light-absorbing (prone to warm the atmosphere) aerosols were likely found in mainland SEA, both for background and high-aerosol events. The light-scattering aerosols were associated with aging processes and hygroscopic growth. The neutral potential, which comprised a mixture of oceanic and local anthropogenic aerosols, was predominant in background aerosols in insular SEA. Further studies should focus on carbonaceous aerosols (organic carbons, black carbon, and brown carbon), the aging processes, and the hygroscopic growth of these aerosols, since they play significant roles in the regional aerosol optical properties.

Chiang Mai suffers from adverse haze associated with heavy biomass burning (BB) during almost every dry season (February to April). As an important source of light-absorbing carbonaceous aerosols (black carbon and brown carbon), BB can have strong radiative effects on local and regional climate. However, studies on characterizing the impacts of BB aerosols on climate in Chiang Mai are quite limited. In this study, we use a global chemical transport model (GEOS-Chem) coupled with the rapid radiative transfer model for GCMs (RRTMG) to estimate the radiative forcing (RF) of BB aerosols in Chiang Mai. Brown carbon (BrC) is included as an absorber and treated as an individual tracer in the model. To our best knowledge, this is the first study to estimate the BrC RF in Chiang Mai. As evaluated, our simulations that were assigned with medium- and high-absorbing kBrC (BrC imaginary refractive index) well reproduces the absorption coefficient of ambient BrC in Chiang Mai. Based on our estimations, 33-40% of total carbonaceous aerosol absorption at 440 nm is attributed to BrC and 60-67% to BC during dry season. As estimated, BrC contributes 14 +/- 3% to the instantaneous RF of total carbonaceous aerosol (IRFCAs) at the top of atmosphere (TOA) and 16 +/- 3% to IRFCAs at surface. Moreover, including BrC in model strengthens (reduces) the surface (TOA) cooling effect of total organic carbon by 9 +/- 5% (9 +/- 3%), indicating the warming effect of BrC in the atmosphere in Chiang Mai.

The effects of black carbon (BC) aerosol radiative forcing on spring rainfall in Southeast Asia are studied using numerical simulations with the NASA finite-volume General Circulation Model (fvGCM) forced with monthly varying three-dimensional aerosol distributions from the Goddard Ozone Chemistry Aerosol Radiation and Transport model (GOCART). During the boreal spring, March-April-May (MAM), BC from local emissions accumulates over Southeast Asia. The BC aerosol layer, which extends from the surface to higher elevation above planetary boundary layer (PBL), absorbs solar radiation and heats the mid-troposphere through a semi-direct effect over regions of large aerosol optical thickness (AOT) and thereby significantly perturbs large-scale and meridional circulations. Results show that anomalous precipitation patterns and associated large-scale circulations induced by radiative forcing by BC aerosol can explain observed precipitation reductions, especially over Southeast Asia. Therefore, BC aerosol forcing may be one of the important factors affecting the spring rainfall trend over Southeast Asia. (C) 2010 Elsevier Ltd. All rights reserved.