Volume 6 Issue 3

Authors: M. Lu; S. Chotpantarat; P. Klongvessa

Abstract: In many flood simulations, critical rainfall duration, defined as duration of rainfall which causes a critical flood, is assumed to be fixed. However, in some area, the critical rainfall duration varies upon its magnitude and assuming the fixed critical rainfall duration may underestimate an extreme peak discharge. The middle and lower Yom basin, Thailand, is one of the areas where a larger flood appears to coincide with longer critical rainfall duration. In this study, we have investigated the variation of critical rainfall duration in that area. The conceptual model was developed from HEC-HMS and HEC-RAS models. The upstream and downstream parts of the area were calibrated separately. Then, uniform 2-, 5-, and 10-year rainfalls with 24-, 48-, and 72-hour durations were simulated. The model successfully reproduced the variation of critical rainfall duration as 48 hours for 2- and 5-year rainfalls and 72 hours for 10-year rainfall. This variation is caused by a high percolation rate over the upstream area. With this percolation, some portion of rainfall over the upstream part is loss. Hence, most of the flood water comes from the downstream part which has short travel time. However, when the rainfall is larger, the influence of percolation is less.

Keywords: Critical Rainfall Duration; Flood; Yom Basin; Percolation


Authors: R.G.C. Jeewantinie Kapilaratne; Minjiao Lu

Abstract: Separation of physical and apparent diurnal fluctuation from dielectrically measured soil water content (SWC) is critical for accurate estimation of temperature related inaccuracies. Evaporation process at soil surface was simulated under synthetic and semi synthetic conditions in HYDRUS-1D environment. At synthetic conditions daily evaporation rate was assumed as 12 mm while evaporation rates at semi synthetic conditions were estimated using meteorological data. This study used 12 soil moisture monitoring stations which represent various climatic and soil conditions to characterize high and low evaporation levels. Simulated SWC at semi synthetic conditions were agreed well with the observed SWC with hourly NASH value ranging from 0.45-0.6. As a consequence of less evaporation related diurnal fluctuations, amplitude of simulated SWC always lesser than that of the observed SWC after eliminating the rainy days and freezing period. For Mongolian sites 6-16% and 3-9% for Unites States’ sites consists of evaporation related amplitude variations of dielectrically measured SWC. Synthetic experiment results indicated that when ground water table getting deeper than 1m evaporation related diurnal fluctuations are disappearing from the near surface soil moisture.

Keywords: Evaporation; HYDRUS-1D; Dielectric Sensors; Soil Moisture


Authors: Guy F. Midgley; Philip G. Desmet; Andrew J. Young; Danni Guo

Abstract: The Succulent Karoo is well known for being rich in species with approximately 5,000 vascular plant species, and has a high floral endemicity. In this study, we investigate the current status of the dwarf succulents of Namibia, as represented by two genera in the Aizoaceae: Conophytum (restricted distribution) and Lithops (wider distribution) and examine possible climate change impacts on these genera by studying the effects on non-rainfall moisture availability (number fog days and relative humidity). Both genera show a contraction and loss of habitat, despite their drought resistant nature and adaptation to the current arid environment. This study demonstrates that climate-change induced alterations to the number of fog days in Namibia results insignificant changes in the distribution of the dwarf succulents, and shows the Atlantic coast and Orange River areas as potential refuge areas for dwarf succulents such as Conophytum and Lithops.

Keywords: Climate Change; Conophytum; Lithops; Dwarf Succulents; Fog; Relative Humidity; Succulent Karoo; Namibia


Authors: Claudia Bittencourt

Abstract: In the 1970s, São Paulo State defined qualitative frameworks for its water resources based on main economic activities to be developed on rivers basins. Sometimes objectives are too far from the actual moment, and that temporal dimension horizons can be better defined on participative and technical basis. Actually is being studied a criteria to subsidize delimitation of intermediary objectives that supports the planning process to be continuously developed on a more intensive progressive perspective. Once the planning have being elaborated on a participative foundation among municipalities, State government and society, a criteria approved by the stakeholders can help on reducing the natural conflicts when stablishing planning products. The proposal presented in the actual paper was approved preliminarily and is submitted to further studies actually.

Keywords: Water Resources; Quality Indicators; Progressive Objectives