Teang Shui Lee

GIS-based scheduling and monitoring of irrigation delivery for rice irrigation system: Part I. Scheduling

A program using geographical information system (GIS) has been developed for the spatial and temporal distribution of irrigation supply for a large-scale rice irrigation project in Malaysia. This study focused on determining water deliveries on a periodic basis during the main (wet) and off (dry) seasons based on spatial and temporal demand. A water balance equation is used to determine the release for each constant head orifice (CHO) within the blocks and compartments. A user interface allows for the selection of a specific area and input of relevant information. The recommended discharges are displayed allowing the manager to view maps, tables and graphs providing a basis for decision making as the season progresses. Comparison of the observed and computed values for the 1997/1998 season in compartment F showed that observed values were higher than the computed values indicating excess supply during the main season. Observed values were lower than computed values during the off-season. The periodic results obtained can then be used to monitor the allocation of irrigation deliveries for improving the water management system.

Recent Trends in Temperature and Precipitation in the Langat River Basin, Malaysia

A study was undertaken to detect long-term trends in the annual and seasonal series of maximum and minimum temperatures. Measurements were taken at 11 meteorological stations located in the Langat River Basin in Malaysia. The rainfall and maximum and minimum temperature data were obtained from the Malaysia Meteorological Department (MMD) and the Department of Irrigation and Drainage (DID) Malaysia. The procedures used included the Mann-Kendall test, the Mann-Kendall rank statistic test, and the Theil-Sen’s slope method. The analytical results indicated that when there were increasing and decreasing trends in the annual and seasonal precipitation and temperature, only the increasing trends were significant at the 95% confidence level. The Theil-Sen’s slope method showed that the rate of increment in the annual precipitation is greater than the seasonal precipitation. A bootstrap technique was applied to explore uncertainty about significant slope values for rainfall, as well as the maximum and minimum temperatures. The Mann-Kendall rank statistics test indicated that most of the trends in the annual and seasonal time series started in the year 2000. All of the annual and seasonal significant trends were obtained at the stations located in the north, east, and northeast portions of the Langat River Basin.

GIS-based scheduling and monitoring irrigation delivery for rice irrigation system Part II. Monitoring

Abstract A computer program with a geographical information system (GIS)-based user-interface was developed to monitor the delivery of irrigation water. The irrigation indices relative water supply (RWS) and cumulative relative water supply (CRWS) were used. The weekly water balance were used to compute these irrigation indices using the recommended irrigation supply given by scheduling program at secondary off-takes regulated by constant head orifices (CHOs) and feedback data at the field level. These computations provide information on the uniformity of water distribution and any shortfall or excess. The program is intended to characterize the irrigation delivery performance on a previous week basis and what decisions to adopt for the next. The weekly results of RWS ranged from 1.01 to 2.24 during the main season, and from 1.01 to 1.87 during the off-season respectively for 1997. The results are displayed allowing the manager to view maps, tables and graphs in a comprehensible form to ease decision-making on water management as the season progresses.

Temporal precipitation trend analysis at the Langat River Basin, Selangor, Malaysia

The Langat River Basin provides fresh water for about 1.2 million people in the Langat and Klang valleys. Any change in the pattern of rainfall could affect the quantity of water in the basin. Studying the pattern of change in rainfall is crucial for managing the available water resources in the basin. Thus, in this study, for the first time, both parametric and non-parametric methods were employed to detect rainfall trend in the basin for the period 1982–2011. The trends were determined at 30 rainfall stations using the Mann–Kendall (MK) test, the Sen’s slope estimator and the linear regression analysis. Lag-1 approach was utilized to test the serial correlation of the series. On the annual scale, it was found that most of the stations in the basin were characterized with insignificant trends. The significant trends were found only at the four stations, namely 44301, 44305, 44320 and 2719001. The results of the seasonal trend analysis showed that most of the stations during the northeast monsoon (NEM) and the inter monsoon 1 (INT1) seasons and half of the stations during the southwest monsoon (SWM) season experienced insignificant positive trends. To the contrary, for the inter monsoon 2 (INT2) season, majority of the stations showed negative trends. It was found that during the NEM season the station 44301, for the INT1 season stations 44301, 2719001 and 3118069 were established as having significant changes, while in the SWM season station 2917001 and during the INT2 season, the stations 2615131 and 44301 showed significant trends. It is worth mentioning that the maximum rainfall occurs in inter-monsoon seasons.

River catchment rainfall series analysis using additive Holt–Winters method

Climate change is receiving more attention from researchers as the frequency of occurrence of severe natural disasters is getting higher. Tropical countries like Malaysia have no distinct four seasons; rainfall has become the popular parameter to assess climate change. Conventional ways that determine rainfall trends can only provide a general result in single direction for the whole study period. In this study, rainfall series were modelled using additive Holt–Winters method to examine the rainfall pattern in Langat River Basin, Malaysia. Nine homogeneous series of more than 25 years data and less than 10% missing data were selected. Goodness of fit of the forecasted models was measured. It was found that seasonal rainfall model forecasts are generally better than the monthly rainfall model forecasts. Three stations in the western region exhibited increasing trend. Rainfall in southern region showed fluctuation. Increasing trends were discovered at stations in the south-eastern region except the seasonal analysis at station 45253. Decreasing trend was found at station 2818110 in the east, while increasing trend was shown at station 44320 that represents the north-eastern region. The accuracies of both rainfall model forecasts were tested using the recorded data of years 2010–2012. Most of the forecasts are acceptable.