Spatio-temporal Variability in Rainfall and Wet-canopy Evaporation within a Small Catchment Recovering from Selective Tropical Forestry.

Within tropical rainforest environments, rainfall pattern and canopy structure regulates the partitioning of water into wet-canopy evaporation and sub-canopy rainfall. These interrelated process then moderate atmospheric water vapour, plant water availability, runoff pathways and soil erosion. Forestry impacts on these atmospheric processes may, therefore, impact on a cascade of other environmental processes. This study, conducted within a 4 km2 experimental catchment in the interior of Northeast Borneo, that was recovering from selective timber harvesting, sought to identify the spatial and temporal structure of the local rainfall, and the impact of forestry on wet-canopy evaporation and lumped, water-balance components. A total of 450 throughfall gauges, 50 raingauges and 40 stemflow gauges were installed and digitally surveyed within the catchment, mostly within a 0. 44 km2 tributary area. Data from these instruments were then supported by those from rainfall recorders and river gauges, and an enumeration of the vegetation patchwork present at 8-years post-logging. Several approaches of statistical modelling were applied, and indicated that the rainfall during the 1997/8 drought-year was (1) highly localised in space, even for regions dominated by convective rainfall, (2) strongly moderated by the local undulating topography, with marked seasonal (monsoon) changes, and (3) delivered primarily as regular, short duration events of low intensity rainfall. The visually classified patchwork of canopy types (supported by a series of biophysical measurements), showed significant differences in rates of wet-canopy evaporation. Smaller quantities of sub-canopy rainfall were observed beneath the disturbed patches of vegetation, in comparison to those beneath undisturbed remnants of primary rainforest. This may have been caused by (i) a greater rate of wet-canopy evaporation, due to enhanced atmospheric turbulence and/or higher surface leaf densities, or (ii) disturbed forest blocks receiving less gross rainfall, due to sheltering by the higher undisturbed canopies. Modelling of the 8-year post-logging water balance data, indicated that both seasonal and inter-annual cycles (related to the El Nino Southern Oscillation) strongly affected the rainfall (P), riverflow (Q) and P-Q' dynamics. On removal of these cyclical components, the analysis indicated that there was no evidence of a change in evapotranspiration (strictly 'P-Q') with the 8-years of forest regeneration. Some of these results were unexpected, and underlined the need for a new emphasis on 'canopy hydrology' within rainforests managed for development and conservation

Pencirian Hidrokimia dinamik sungai Kimanis dan Sungai Mandahan, Papar

Kajian ke atas kandungan nutrien (nitrat dan fosfat) dan beberapa parameter kualiti air lain di Sungai Kimanis telah dilakukan di tiga lokasi di sepanjang sungai tersebut. Turut dikaji adalah kualiti air di Sungai Mandahan dan muara Sungai Benoni. Sampel-sampel air sungai dan di muara sungai diperolehi selama tiga bulan bcrmula dari Oktober hingga Disembcr 2002. Kerja-kerja penganalisisan telah dilakukan di makmal Universiti Malaysia Sabah. Hasil kajian menunjukkan julat kepekatan bagi nitrat, 0.00 - 0.4 mgr' dan fosfat, 0.03 - 0.24 mgr'. Kepekatan nutrien di Sungai Kimanis adalah relatif lebih . tinggi pada bulan Oktober berbanding dengan bulan-bulan kemudiannya, yang diakibatkan oleh luahan air sungai yang lebih ban yak pada bulan tersebut. parameter parameter seperti suhu, pH, DO, BOD, kemasinan, kekonduksian elektrik, minyak dan gris telah menunjukkan Sungai Kimanis masih berada dalam kategori kelas 11 mengikut piawaian kualiti air negara. Kualiti air di muara Sg. Benoni dan Sg. Kimanis dipengaruhi oleh air pasang surut. Kandungan Zn dalam sedimen sungai agak rendah, manakala eu adalah agak tinggi nilainya

Understanding of groundwater salinity using statistical modeling in a small tropical island, East Malaysia

This paper presents an understanding of groundwater salinity by identification of effective factors using chemometric methods (cluster analysis and multiple linear regressions) in Manukan Island, Sabah. Local groundwater and environmental properties were used to explore the effective factors of groundwater salinity. Cluster analysis showed salinity and chloride illustrated the highest similarities. Electrical conductivity and total dissolved solids were also grouped in the same cluster. Seawater is the only chloride source in groundwater of Manukan Island demonstrated an indication of seawater mixing in freshwater. It is an effect of upward movement of the seawater by pumping activities. Precipitation and evapotranspiration (environmental condition) with hydraulic heads were clustered together to show that they also influence salinity concentration in groundwater. Multiple linear regressions showed descending order of the factors from chloride (the largest contribution) to evapotranspiration (the smallest contribution) and illustrated the contribution to groundwater salinity in Manukan Island. The integrated results using chemometric methods have provided a way to identify the effective factors on groundwater salinity. This similar approach and resulting equation can be applied in other small tropical islands with alike hydrogeological condition and limited information available for a better understanding of its groundwater salinity

A brief review on groundwater studies in Malaysia.

Groundwater studies related to coastal and small islands in Malaysia are briefly reviewed. Perspectives are addressed as three aspects: (a) study location, where groundwater studies in Malaysia are conducted in different types of coastal and small islands (b) methods, namely numerical modeling, geophysical investigations, hydrochemical analysis and geochemical modeling applied in groundwater studies of Malaysian coastal environment and small islands; (c) types of studies, where most of groundwater studies are more focused in investigating the groundwater resources and management as well as seawater intrusion. This review revealed that main objectives in most of Malaysian groundwater studies in coastal and small islands are groundwater resources, management as well as seawater intrusion problem. This showed that groundwater studies in Malaysia are clearly needed to be increased and strategized by smart partnerships, diverse groundwater type of studies by identification of effective methods as well as capacity building improve and develop skills, expertise and knowledge in the management. Future studies should give a focus in other types studies in utilization of this resource in order to fill in the knowledge gap of groundwater to provide clear direction in sustainable development of this precious resource

Recharge and aquifer response: Manukan islands aquifer, Sabah, Malaysia

Manukan Island is a small island located in North-West of Sabah, Malaysia was used as a case study area for numerical modeling of an aquifer response to recharge and pumping rates. The results in this study present the variations of recharge into the aquifer under the prediction simulations. The recharge rate increases the water level as indicated by hydraulic heads. This shows that it can alter groundwater of Manukan Island which has been suffering from an overexploration in its unconfined the aquifer. The increase in recharge rate (from 600 mm/year to 750 mm/year) increases the water level indicated by hydraulic heads. A reduction in pumping rate (from 0.072 m3/day to 0.058 m3/day) not only increases the amount of water levels in aquifer but also reduces the supply hence a deficit in supply. The increase in hydraulic heads depends on the percentage reduction of pumping and recharges rates. The well water has 1978.3 mg/L chloride with current pumping (0.072 m3/day) and recharge rates (600 mm/year). However, with an increased of recharge rate and current pumping rate it has decreased about 1.13%. In addition, reduction in pumping rate made the chloride concentration decreased about 2.8%. In general, a reduction in pumping with an increase in recharge rate leads to a decreased in chloride concentrations within the vicinity of cone of depression. Next, to further develop the numerical model, the model should focus on climate change variables such as consequences of climate change are increase in air temperature, increase in sea surface temperature, and more extreme weather conditions. These parameters are considered critical parameters for climate change impact modeling in aquifers. The behavior of the aquifer and its sustainable pumping rate can be done by applying a computer modeling component

Parsimonious spatial representation of tropical soils within dynamic rainfall-runoff models

Introduction Models are used increasingly to simulate hydrological processes within tropical regions. There is now a wealth of publications addressing evaporation modelling (particularly wet-canopy evaporation) of local areas of tropical forest in, for example, Niger (Gash et al., 1997), Guyana (Jetten, 1996), Puerto Rico (Schellekens et al., 1999), Columbia (Marin et al., 2000) and Indonesia (Asdak et al., 1999; van Dijk and Bruijnzeel, 2001). Elsewhere in this volume, Roberts et al. provide an overview of evaporation processes and modelling. Other modelling studies have addressed the impact of such tropical evaporation on regional climates and global circulation (e.g. Polcher and Laval, 1994; Zeng, 1999; Zeng and Neelin, 1999; Zheng et al., 2001). New studies using time-series models are highlighting the effects of cycles in the rainfall, such as the El Nino Southern Oscillation (ENSO) on tropical evaporation, riverflow and water quality (e.g. Zeng, 1999; Chappell et al., 2001; Krishnaswamy et al., 2001; Whitaker et al., 2001; Chappell, Tych et al., this volume). Similarly, models that simulate the generation of riverflow from the rainfall received by a tropical catchment are also beginning to be applied more frequently. These models include: Metric-conceptual models of waterflow, based upon transfer functions. For example, application of the DBM modelling approach to a nested catchment system in Malaysian Borneo (Chappell et al., 1999a) and the application of IHACRES to a large Thai basin (Scoccimarro et al., 1999). Conceptual models of waterflow based upon stores and pre-determined empirical relationships. For example, application of the Nash model to Kenyan catchments (Onyando and Sharma, 1995), the Modhydrolog model to a tropical catchment (Chiew et al., 1996), the Reservoir-Water-Balance-Simulation model to Namibian catchments (Hughes and Metzler, 1998), and the HBV-96 model (discussed in Barnes and Bonell, this volume) to catchments in Zimbabwe, Tanzania and Bolivia (Liden and Harlin, 2000).[&]. © UNESCO 2005 and Cambridge University Press, 2009

Numerical simulation of seawater intrusion in Manukan Island, East Malaysia.

Purpose – This paper aims to define the current and potential extent of seawater intrusion in Manukan Island under different scenarios of varying recharge and pumping rates. The calibrated model was also used to predict the extent of seawater intrusion in low lying area of Manukan Island for two years with all conditions assumed to remain the same as those in December 2009. Design/methodology/approach – Different scenarios of varying recharge and pumping rates based on threats received by Manukan Island were investigated. El-Nino events and overpumping are represented by varying recharge and pumping rates. Simulation was done using SEAWAT-2000, the latest modeling software available in groundwater modeling that couples flow and transport together. Findings – The seawater-freshwater mixing ratio moves landwards after two years of simulation in Scenario 1. In order to control overpumping in this study area, Scenario 2 has resulted in backward movement of the 1.4 percent seawater-freshwater mixing ratio toward the coast after two years of prediction. The current contamination of the coastal aquifers by seawater intrusion will be more severe with an impact of El-Nino events on groundwater resources depletion in Scenario 3. Reductions of pumping and recharge rates in Scenario 4 have worsened the seawater intrusion problem. With the aid of artificial recharge in Scenario 5, highest hydraulic heads and lowest chloride concentration were observed. Practical implications – The sustainable groundwater management selected for Manukan Island's current situation will be Scenario 2. In view of the effects of El-Nino events in the future, Scenario 5 can be implemented to restore groundwater resources. The numerical model has showed the groundwater condition during El-Nino events and overpumping illustrated that simulation modeling is an excellent tool to understand the behavior and management of an aquifer system. The output of simulation modeling via numerical model provides a framework toward groundwater management. Thus, current study output with similar approach which will restore groundwater (artificial recharge and reduction of pumping rate) can be applied in other small islands of similar hydrogeological condition and stresses for the purpose of groundwater resource protection