Priyantha Jayakody

The Projected Impact of Climate Change on Water Availability and Development in the Koshi Basin, Nepal

Abstract Water has been identified as a key resource for Nepals economic growth. Although the country has 225 billion cubic meters of water available annually, less than 7% has been utilized. Climate change is a frequent topic in national development discussions in part because of its possible impact on future water availability. This study assessed the likely impact of climate change on water resources development in the Koshi River basin, Nepal, using the Soil and Water Assessment Tool to generate projections for the 2030s and 2050s. Results suggested that the impacts are likely to be scale dependent. Little impact is projected at annual, full-basin scales; but at sub-basin scale, under both the IPCCs A2 and B1 scenarios, precipitation is projected to increase in the upper transmountain subwatersheds in the 2030s and in most of the basin in the 2050s and to decrease in the lower sub-basins in the 2030s. Water yield is projected to increase in most of the basin except for the A2 scenario for the 2030s. Flow volumes are projected to increase during the monsoon and postmonsoon but decrease during the winter and premonsoon seasons. The impacts of climate change are likely to be higher during certain seasons and in some sub-basins. Thus, if infrastructure is in place that makes it possible to store and transfer water as needed, the water deficit due to any changes in rainfall or flow patterns could be managed and would not be a constraint on water resources development. The risks associated with extreme events such as floods and droughts should, however, also be considered during planning.

Hydrological impacts of inflow and land-use changes in the Gorai River catchment, Bangladesh

This study looks at the changes in water balance in the Gorai River Catchment in the Bangladesh delta before and after operationalization of Farakka Barrage. Results show that inflow into the catchment has decreased, but major changes in land use within the catchment have also impacted runoff. Model scenarios demonstrate that although increasing inflow from upstream is the most effective method to increase dry season flows into the delta, reduction in cultivation of water-intensive crops would provide an alternative solution.

Evaluating Spatial and Temporal Variability of Fecal Coliform Bacteria Loads at the Pelahatchie Watershed in Mississippi

ABSTRACT Bacterial contaminations of surface waters are an increasing concern for scientists and public health agencies because pathogenic bacteria can cause adverse effects on human health. This research was performed to investigate spatial and seasonal variability of fecal coliform bacteria (FCB) concentrations in the Pelahatchie watershed (527 km2) in Mississippi, USA. Livestock manure, poultry litter, and effluent from failing septic systems were identified as major sources of FCB in the Pelahatchie watershed. The Soil and Water Assessment Tool (SWAT)/microbial sub-model was applied, and model-simulated FCB concentrations were compared with the monthly measured FCB concentrations (years 2001–2008) at the outlet of the watershed. New methodologies were introduced to incorporate bacteria loads into the bacteria model. Results showed coefficients of determination (R 2) of 0.71 to 0.75, and Nash-Sutcliffe efficiency index (NSE) of 0.67 to 0.75 during the bacteria models calibration and validation periods, respectively. Seasonal analysis of the model-simulated results determined the highest bacteria concentrations in January, whereas the lowest concentrations were simulated in June. Furthermore, the FCB contributions to the watershed outlet from the sources of contamination varied with time of year. This study will help watershed managers to implement best management practices for improvement of water quality.

Relationships between water table and model simulated ET

This research was conducted to develop relationships among evapotranspiration (ET), percolation (PERC), groundwater discharge to the stream (GWQ), and water table fluctuations through a modeling approach. The Soil and Water Assessment Tool (SWAT) hydrologic and crop models were applied in the Big Sunflower River watershed (BSRW; 7660 km(2) ) within the Yazoo River Basin of the Lower Mississippi River alluvial plain. Results of this study showed good to very good model performances with the coefficient of determination (R(2) ) and Nash-Sutcliffe efficiency (NSE) index from 0.4 to 0.9, respectively, during both hydrologic and crop model calibration and validation. An empirical relationship between ET, PERC, GWQ, and water table fluctuations was able to predict 64% of the water table variation of the alluvial plain in this study. Thematic maps were developed to identify areas with overuse of groundwater, which can help watershed managers to develop water resource programs.

Assessing Climate Variability Impact on Thermotolerant Coliform Bacteria in Surface Water

ABSTRACT This study investigated the impacts of climate variability on thermotolerant coliform bacteria (TCB) transport in the Upper Pearl River watershed (UPRW) in Mississippi. The Soil and Water Assessment Tool (SWAT) was applied using daily observed stream flows and TCB concentration data. The SWAT model was successfully calibrated and validated using both manual and automatic methods from February 2011 to June 2012 (NSE and R2 up to 0.79). The Long Ashton Research Station Weather Generator (LARS-WG), a stochastic weather generator, with the global climate model, CCSM3, which was developed by the U.S. National Center for Atmospheric Research (NCAR) was used for future climate variability simulations. The Special Report on Emissions Scenarios (SRES) A1B of the Intergovernmental Panel on Climate Change (IPCC) was simulated for the mid (2046–2065) and late (2080–2099) 21st century. The SWAT model simulated TCB concentrations in surface water and demonstrated reasonable performances (R2 up to 0.59 and NSE up to 0.58). During mid-century climate, average monthly TCB levels increase to 175%, while late-century average monthly TCB levels increase to 297% from the watershed. Although late-century climate variability impacts were determined more critical than mid-century climate impacts, appropriate watershed management practices are required to adapt to maintain and improve water quality.

Identifying critical areas of bacteria loading in the Upper Pearl River Watershed

Origin, contamination and transportation of fecal bacteria are largely unknown. Modeling of bacteria loadings from small scale watersheds using more site specific information can help to scale up modeling study to large scale watersheds.