Assessment of Mountain Range Effects in Peninsular Malaysia on Catchment and Rainfall Using GIS Spatial Analysis. A project thesis submitted to the Civil Engineering Program Universiti Teknologi PETRONAS As partial fulfillment of the requirement for. Alhamdulillah, praise be to Allah Almighty for giving the author the opportunity, health and ability to complete this final year project on “Assessment of Mountain Range Effects in Peninsular Malaysia on Catchment and Rainfall Using GIS Spatial Analysis”.
This project is a partial fulfillment of the requirement for Bachelor of Engineering (Hons.) in Civil Engineering for the final semester of the final year. The main mountain range in peninsular Malaysia is the Titiwangsa mountain range that divides the peninsula between its east and west coasts. This paper studies the effects of the mountain range on the catchment and rainfall using GIS tools in the hope of understanding how the mountain ranges in Peninsular Malaysia namely the Titiwangsa mountain range affected the water catchment and rainfall.
Objectives
It is error prone, tedious and subject to individual judgment which is not efficient as stated by Abdallah et al. Other than that, rainfall analysis using isohyet is also not effective when using the conventional method like Thiessen, Arithmetic mean and Isohyet method, which requires long and tedious calculations for creation of isohyet. Therefore, automated watershed boundary delineation and isohyet creation are used to replace the conventional method by using computer-aided method, such as the use of GIS technology that has the potential to overcome many conventional analysis problems (Oliver, David & Ian, 1997).
Study Area
It is assumed for the delineation of the watershed that the catchment area depends solely on the contour which does not take into account the entire topography of the land (eg man-made structure such as building). The isohyte study is based on the cumulative rainfall data for five months based on the typical northeast monsoon and southwest monsoon in Malaysia. Judgment that is made for the isohytes is based on the effect of the land height, but not discussed in detail other rainfall causes such as the tropical depression and typhoon.
The scope of the first phase study is both research and the collection of necessary data about the study area. In addition, the objective of the first phase is to use the software and the related theoretical knowledge and practice in the implementation of the project. The second phase, which is the implementation part, includes the process of obtaining the delineation of watersheds and isohyets for the study area as a result of the project.
LITERATURE REVIEW
Orographic Precipitation (Minder & Roe, 2009)
Orographic influences can be pronounced on spatial scales ranging from the size of individual hills to the scale of larger mountain ranges, and on temporal scales from the duration of a short snowstorm to long-term climatology. Almost all orographic influences are basically the result of topographically conditioned rising and falling atmospheric movements that cause condensation and evaporation. However, these basic forces combine with a wide range of dynamical and microphysical processes to shape the precipitation distribution.
Since different physical processes may be important for different storms and for different ranges, the impacts of orographic precipitation can take many forms.
DEM Pre-Processing for Efficient Watershed Delineation (Dean &
The choice of the threshold value and its impact on delineation performance will be discussed later. Sub-catchment areas (in raster format) are defined for each of the stream connections in the stream link grid. The FWD methodology described in this article enables efficient and consistent watershed delineation on DEMs of all sizes.
The rendering speed can be controlled by the user during the pre-processing stages and can be on the order of five to ten seconds per watershed on most of today's desktop systems, allowing for truly interactive operation. The required pre-processing needs to be done only once for a given DEM and may be done in a different location than where the actual definition work will be done. This allows preprocessing of regional datasets that are then distributed to end users, who can immediately apply delineation tools to that dataset.
The Impact of the Typhoon to Peninsular Malaysia on Orographic Effects (Fuyi, Hwee & Khiruddin, 2011)
Although the typhoon is not in a direct path to Peninsular Malaysia, the tail effect of the typhoon is significant. The intensity of the rainfall can be referred to the rainfall scale on the images in Figure 2.4. Rainfall patterns are affected by typhoon Ketsana as the atmospheric circulation is changed based on the typhoon movement.
The rainfall distribution pattern in northeastern Peninsular Malaysia (see Figures 2.4a to 2.4e) tended to shift towards the typhoon center as the typhoon system has a lower pressure center. The wind blows towards the center of the typhoon's low pressure, so the clouds will also follow the wind's path. Thus, rainfall distribution patterns tend to be distributed along the outer track of the typhoon.
Therefore, it is believed that rotation of the typhoon can change low level atmospheric circulation, as the phenomena proved that typhoon is able to change the atmospheric circulation on synoptic scale. Many previous studies have been made for the typhoon-orography interaction over Taiwan Island which is always hit by the typhoon. Nevertheless, parts of the rainfall continue to move forward due to the typhoon development system.
This is because the rainfall site is located in the southwest of the typhoon's outer flow. On the other hand, the rainfall has crossed Mount Tahan because of the typhoon system forcing. The rain cloud over the South China Sea will apparently join the typhoon system due to the high low pressure system.
Moreover, the rate of precipitation is increasing and its coverage becomes more and more extensive when the rain clouds are close to the typhoon system.
METHODOLOGY
- Collecting Relevant Data
- Watershed Delineation
The software is used to create both the watershed delineation and the isohyte for the study area. The process flow of the project is illustrated in Figure 3.1 below and the detailed process methodology is explained in detail in achieving the objectives. Since the manipulated variable for the study is the height of the mountain, Cameron Highland is chosen for high altitude mountain and Hulu Langat for low altitude.
Jabatan Ukuran dan Pemetaan (JUPEM) digital map and Jabatan Saliran dan Pengairan (JPS) rainfall data must be available for the purpose of the study. In the case of precipitation data, the intensity of precipitation data (in millimeters) is obtained every 15 minutes from the automatic recorder of precipitation stations. It is very important to set the map projection using the Define Projection tool in the first step.
Once the projection is set up, the Topo to Raster tool is selected and the shapefile is used as the input feature and saved as CamDEM30. The Fill tool is used and DEM30 is used as the input surface raster and the output is saved as CamFill. An illustration of data input and output is shown in Figure 3.5 where the encoding of each direction is shown.
The Basin tool is used to identify the basins flowing to each outlet on the map edge and the CamFlowDir is used as the input flow direction grid and saved as CamBasin. The Raster Calculator tool is used with CamFlowAcc as input and saved as CamStream, as shown in Figure 3.11. Use the Stream Link tool and specify CamStream and CamFDirClip as the input stream grid and input stream direction grid, respectively, to obtain the stream link, as shown in Figure 3.13.
The final output of the delineated watershed and stream network is shown in Figure 3.14. Using the IDW tool, the shapefile is used as the input point features with the rainfall as the Z value field and the output file is saved as IDW1103. The first input features used for the Intersect tool is CamCont1103 and the second input is CamBasinPolygon.
RESULT AND DISCUSSION 4.1 Watershed Delineation
- Cell Size of DEM
- Threshold Area for Stream Network
- Comparison of Isohyet
- Satellite Proving
Some other assumptions have been made about the threshold area; the results obtained are shown in Figure 4.2 below. The isohyet created in this study includes the isohyet during the northeast and southwest monsoon in Cameron Highland and Hulu Langat. Below is the isohyet comparison between the northeast and southwest monsoon at Cameron Highland and Hulu Langat.
The six rainfall stations in Cameron Highland experience cumulatively higher rainfall (the highest amount displayed is 1200 mm of rain) during the northeast monsoon and noticeably lower rainfall during the southeast monsoon (the highest amount displayed is 950 mm). Hulu Langat, on the other hand, does not show much difference between the cumulative rainfall of the northeast monsoon and the southwest monsoon. Thus, based on the orographic theory of precipitation, it can be concluded that the reason for the higher rainfall during the northeast monsoon at Cameron Highland is due to its altitude.
Thus, according to the orographic rainfall theory, the rainfall will be less or none at Cameron Highland (which is now the leeward side) due to the height of the mountain causing the rain to fall more on the windward side compared to the leeward side. page. As for the Hulu Langat area, it is mentioned before that there is no significant difference between northeast and southwest monsoon in terms of rainfall intensity. Thus, it can be deduced that the height of the Hulu Langat area is not enough for the orographic precipitation to occur.
Rainfall in the Hulu Langat area may be caused by other factors such as the tropical depression. To prove the orographic rainfall along the mountain range, hourly satellite images showing the rainfall estimate are taken from 0000 on 29 January 2011 until 24:00 on 31 January 2011. It can be said that the precipitation cloud "stuck" as it passed through the mountain range, proving that orographic precipitation can be seen along the mountain range in Peninsular Malaysia.
The importance of this orographic precipitation study is to understand how the mountain in Malaysia is exposed to orographic precipitation.
CONCLUSIONS AND RECOMMENDATIONS
Advances on the theory of orographic precipitation, in: Willett SD, Hovius N, Brandon M, Fisher DM, (Eds), Tectonics, Climate, and Landscape Evolution: GSA Special Paper 398, Geological Society of America, Boulder, CO, 1- 16 .
APPENDICES
Rainfall stations located within the mountain ranges are chosen by studying the map provided by JPS. Figure above showing all hydrological stations
Rainfall stations locations are determine by the inventory provided by JPS. Figure above showing some inventory of rainfall stations in Pahang
Raw rainfall data are calculated and summarize for further study
DEM data sources is used as guideline for the selection of appropriate DEM cell size
All 72 hours of satellite images are obtained and studied to see the pattern of the rainfall precipitation estimation
