Hydroclimate variability and long-lead forecasting of rainfall over Thailand by large-scale atmospheric variables

Abstract

The development of statistical relationships between local hydroclimates and large-scale atmospheric variables enhances the understanding of hydroclimate variability. The rainfall in the study basin (the Upper Chao Phraya River Basin, Thailand) is influenced by the Indian Ocean and tropical Pacific Ocean atmospheric circulation. Using correlation analysis and cross-validated multiple regression, the large-scale atmospheric variables, such as temperature, pressure and wind, over given regions are identified. The forecasting models using atmospheric predictors show the capability of long-lead forecasting. The modified k-nearest neighbour (k-nn) model, which is developed using the identified predictors to forecast rainfall, and evaluated by likelihood function, shows a long-lead forecast of monsoon rainfall at 7–9 months. The decreasing performance in forecasting dry-season rainfall is found for both short and long lead times. The developed model also presents better performance in forecasting pre-monsoon season rainfall in dry years compared to wet years, and vice versa for monsoon season rainfall.

Editor Z.W. Kundzewicz

Citation Singhrattna, N., Babel, M.S. and Perret, S.R., 2012. Hydroclimate variability and long-lead forecasting of rainfall over Thailand by large-scale atmospheric variables. Hydrological Sciences Journal, 57 (1), 26–41.     

Modelling considerations for examining the mean and unsteady flow in a simple urban-type street canyon

With very few exceptions, just about all limited area models (LAMs) used in operational NWP and regional climate modeling use the Davies (Q J R Meteorol Soc 102:405–418, 1976) relaxation lateral boundary conditions (LBCs), even though they make no effort to respect the basic mathematics of the problem. While in the early stages of the primitive equation LAM development in the seventies numerous schemes have been proposed and tested, LAM communities have eventually for the most part settled on the relaxation LBCs with few questions asked. An exception is the Eta model used extensively at NCEP and several other centers, in which the Mesinger (Contrib Atmos Phys 50:200–210, 1977) LBCs are used, designed and based on knowledge available before the introduction of the relaxation scheme. They prescribe variables along the outermost row of grid points only; all of them at the inflow points and one less at the outflow points where the tangential velocity components are extrapolated from inside of the model domain. Additional schemes are in place to suppress separation of gravity-wave solutions on C-subgrids of the model’s E-grid. A recent paper of Veljovic et al. (Meteor Zeitschrift 19:237–246, 2010) included three 32-day forecasts done with both the Eta and the relaxation LBCs and the comparison of some of their verification results. Here we extend this experiment by three additional forecasts to arrive at an ensemble of six members run with both schemes, and present a more complete discussion of results. We in addition show results of one of these forecasts in which the linear change of relaxation coefficients was replaced by the change following the recommendation of Lehmann (Meteorol Atmos Phys 52:1–14, 1993). We feel that the results of our two verification schemes strongly suggest the advantage of the Eta over the conventional relaxation scheme, thereby raising doubts as to the justification for its use.     

Late Weichselian to Holocene paleoenvironments in the Barents Sea

Paleoceanographic changes since the Late Weichselian have been studied in three sediment cores raised from shelf depressions along a north–south transect across the central Barents Sea. AMS radiocarbon dating offers a resolution of several hundred years for the Holocene. The results of lithological and micropaleontological study reveal the response of the Barents Sea to global climatic changes and Atlantic water inflow. Four evolutionary stages were distinguished. The older sediments are moraine deposits. The destruction of the Barents Sea ice sheet during the beginning of the deglaciation in response to climate warming and sea level rise resulted in proximal glaciomarine sedimentation. Then, the retreat of the glacier front to archipelagoes during the main phase of deglaciation caused meltwater discharge and restricted iceberg calving. Fine-grained distal glaciomarine sediments were deposited from periodic near-bottom nepheloid flows and the area was almost permanently covered with sea ice. The dramatic change in paleoenvironment occurred near the Pleistocene/Holocene boundary when normal marine conditions ultimately established resulting in a sharp increase of biological productivity. This event was diachronous and started prior to 10 ¹⁴C ka BP in the southern and about 9.2 ¹⁴C ka in the northern Barents Sea. Variations in sediment supply, paleoproductivity, sea-ice conditions, and Atlantic water inflow controlled paleoenvironmental changes during the Holocene.     

Occurrence of phthalate diesters in rivers of the Paris district (France)

The occurrence and fate of six phthalate esters were investigated in the River Seine and two tributaries in the Paris area, at six sites from upstream to downstream, throughout different seasons, with special attention given to a flood episode. At all sites, except the River Marne, whatever the period, diethylhexyl phthalate (DEHP) displayed the highest concentration (0·323–0·779 µg l^?1 as mean values), followed by di‐n‐butyl phthalate (DnBP; 0·211–0·526 µg l^?1 as mean values), which is consistent with the production pattern. High phthalate concentrations appeared to be related to population density and industrial distribution. The strongest values were located downstream from wastewater treatment plant effluent inputs. Seasonal variations were closely related to river flow and air and water temperature. The annual evolution of phthalates was linked to the hydrological conditions. During the flood episode at Paris, the DEHP concentration displayed a sharp increase (260 to 1123 ng l^?1) occurring 9 days before the flood peak. The simultaneous fluctuations of NH₄, typical of domestic origin, and of DEHP suggests a similar origin from combined sewer overflows for both compounds. Other elevated values corresponded to the highest precipitation amounts, and demonstrated the contribution of non‐point‐source runoff and wastewater overflow to DEHP inputs. The DEHP concentration relationship with river flow displayed a clockwise hysteresis loop, corresponding to a ‘first‐flush’ effect in which the finite supplies are swept along in the early stage of the flood. Annual fluxes for 2004 at Paris were 2257 kg of DEHP and 1613 kg of DnBP. The flood period seemed to have a minor impact on annual phthalate transport (29·5% and 41% of the total for DEHP and for DnBP, respectively), which is contrary to annual suspended solids transport (69%). Copyright © 2007 John Wiley & Sons, Ltd.     

High to low velocity succession in the upper crust related to tectonic emplacement: Tras os Montes-Galicia (Iberia), Brittany and Limousin (France)

Summary. Seismic probing of the upper crust in a catazonal massif in Tras os Montes, Hercynian Iberia, demonstrates the absence of a root towards the lower crust and favours a mechanism of thrust and nappe emplacement. Similar high to low velocity successions in the upper crust are evidenced in particular segments of the Hercynian domain of France. All these occurrences are related to a type region to which a particular meaning has been given in a recent plate tectonics interpretation of the Hercynian orogenesis. This model, implying large-scale nappe displacement and intracrustal thrusts furnishes in turn a general mechanism for the tectonic formation of upper crustal high and low velocity layers of limited extent in orogenic cycles.     

Desalination of a sedimentary rock aquifer system invaded by Pleistocene Champlain Sea water and processes controlling groundwater geochemistry

The objective of this study was to identify geochemical processes and Quaternary geological events responsible for the variations in groundwater geochemistry observed in a sedimentary rock aquifer system, including brackish to saline groundwater. Inorganic constituents and environmental isotopes were analyzed for 146 groundwater samples. Dissolution of carbonates dominates in recharge areas, resulting in Ca-, Mg-HCO₃ groundwater. Further along flow paths, under confined conditions, Ca²⁺–Na⁺ ion exchange causes groundwater evolution to Na-HCO₃ type. Na-Cl groundwater is also found and it falls on a seawater mixing line. Using conservative tracers, Cl⁻ and Br⁻, the original Champlain Sea water is shown to have been, in the region, a mixture of about 34% seawater and 66% freshwater, a composition still retained by some groundwater. Na-Cl groundwater thus results from mixing with former Champlain Sea water and also from solute diffusion from overlying marine clay. The system is thus found to be at different stages of desalinization, from the original Champlain Sea water still present in hydraulically stagnant areas of the aquifer to fully flushed conditions in parts, where more flow occurs, especially in recharge zones. The geochemical processes are integrated within the hydrogeological context to produce a conceptual geochemical evolution model for groundwater of the aquifer system.     

Hydrogeochemistry and groundwater origin of the Basses-Laurentides sedimentary rock aquifer system, St. Lawrence Lowlands, Québec, Canada

A comprehensive hydrogeochemical study was carried out in the Paleozoic Basses-Laurentides sedimentary rock aquifer system in Québec over a 1500 km² study area. Groundwater samples were collected at 153 sites, characterizing all geological and hydrogeological units to a maximum depth of 140 m. Groundwater was analyzed for major, minor and trace inorganic constituents, stable isotopes δ ²H, δ ¹⁸O, and δ ¹³C of dissolved inorganic carbon (DIC), and some samples were analyzed for ³H, and ¹⁴C of DIC. The regional distribution of groundwater types shows that the hydrogeological conditions exert a dominant control on the major ions chemistry of groundwater. Preferential recharge areas are characterized by tritiated Ca-Mg-HCO₃ groundwater, and confined conditions by submodern Na-HCO₃ and Na-Cl groundwater types. Two groundwater end-members are identified in the aquifer system, modern meteoric water and Pleistocene Champlain Sea water. The region displays significant variations of groundwater geochemistry and quality controlled by glaciation, Champlain Sea invasion, lithological rock diversity, and flow system scales. This situation leads to varied groundwater types and origins within a restricted area.     

Caractérisation de zones sources de DNAPL à l'aide de traceurs bisolubles : mise en évidence d'une cinétique de partage

Pollution source characterization by the Partitioning Interwell Tracer Test method requires the assessment of the partitioning coefficient of the tracers with the pollutant. Experiments conducted on batch tests (static) and laboratory columns (dynamic) indicated a partitioning kinetics between the reactive tracer (4-methyl 2-pentanol) and the organic phase (trichlorethene); the partitioning coefficient decreases when the flow velocity through the porous medium increases. This partitioning kinetics has been confirmed by the interpretation of the tracer breakthrough curves with a first-order kinetic transfer model. To cite this article: M. Bohy et al., C. R. Geoscience 336 (2004).