Effects of changes in rainfall and land cover patterns on surface runoff in the Ayung watershed in Bali, Indonesia
Issued Date
2022
Copyright Date
2022
Resource Type
Language
eng
File Type
application/pdf
Access Rights
open access
Rights
ผลงานนี้เป็นลิขสิทธิ์ของมหาวิทยาลัยมหิดล ขอสงวนไว้สำหรับเพื่อการศึกษาเท่านั้น ต้องอ้างอิงแหล่งที่มา ห้ามดัดแปลงเนื้อหา และห้ามนำไปใช้เพื่อการค้า
Rights Holder(s)
Mahidol University
Suggested Citation
Dharamayasa, I Gusti Ngurah Putu, 1978 - (2022). Effects of changes in rainfall and land cover patterns on surface runoff in the Ayung watershed in Bali, Indonesia. Retrieved from: https://repository.li.mahidol.ac.th/handle/123456789/114188
Title
Effects of changes in rainfall and land cover patterns on surface runoff in the Ayung watershed in Bali, Indonesia
Author(s)
Advisor(s)
Abstract
Climate change is associated with changes in temperature, humidity, and rainfall patterns.While increased rainfall causes flooding in a watershed, a lack of enough rainfall leads to drought and waterscarcity. Moreover, land conversions of forests and farmlands to residential and commercial zones, which are needed to deal with population growth, urbanization, and infrastructure development activities, cause increasing surface runoff that may also contribute to flooding. The Ayung River watershed, the largest watershed area on the island of Bali in Indonesia, has been experiencing environmental disasters of flash flooding caused by climate change induced rainfall coupled with increased surface runoff due to land cover changes. This study is aimed at evaluating the potential for flooding or drought in the Ayung watershed dueto the effects of changes in rainfall and land cover.Firstly, future rainfall forecasts were generated using the global climate model (GCM)established by the National Center of Atmospheric Research in the United States for the most likely climatechange scenario (NCAR). The Indonesian meteorological department provided rainfall data for the years 2006to 2018 from eight rainfall stations located across the Ayung watershed (Sading, Mambal, Tegalalang,Tampaksiring, Bedugul, Pengotan, Gitgit, and Kedisan). Simulated rainfall from the NCR model for the same time period was compared to observed rainfall for four climate change scenarios (RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5). Rainfall projections were made for the period of 2019-2030 using the most appropriate scenario(RCP 6.0) for the Ayung watershed. Future predictions indicate a decrease in rainfall, leading to the potential for insufficient water supply in the future.The land cover maps for the four categories, namely forest, agricultural land, settlements, and grasslands, were obtained for the period 2006-2019 by manually digitizing the maps given by Google Earth at a scale of 1:20,000 in order to examine the land cover changes in the Ayung watershed. Following that, two approaches were used to calculate runoff coefficients in the Ayung watershed: (1) Hassing method and (2)Cook method. According to the findings, agriculture and forest areas were reduced by 647.8 ha and 553.1 ha, respectively, due to conversion to fast-growing grasslands or unproductive land. Such changes in land cover have a detrimental impact since they raise the runoff coefficient in the area. The runoff coefficient wascontinuously greater than 0.6 during the study period (high-risk category). Flood risk maps could be created topinpoint flood-prone locations. Several places in the Ayung watershed appear to be in high flood risk categories(runoff coefficient >0.6) based on runoff coefficient mapping between 2012 and 2019. The situation worsens as forests and farmlands are converted to grasslands and settlements, resulting in a higher runoff coefficient.Several portions of Denpasar, in particular, have seen a considerable increase in the runoff coefficient (>5%)from 2012 to 2019. As a result of the increased surface runoff, there is a high risk of flooding in the area. Theheightened risk of floods in Denpasar, a densely populated city, could have a negative impact on its residents.Finally, flood modeling was carried out for several return periods including 5, 10, 25, 50, and100 years, using the HEC-RAS software, to determine the effect of flooding on settlements in the Ayungwatershed. The modeling predicted water levels and changes in flood depths in four sections in the city ofDenpasar, namely Penatih, Kesiman, Kesiman Petilan, and Kesiman Kertalangu, were predicted to experiencefairly serious flooding in the future.Changes in land cover patterns have increased the possibility of floods in the Ayung watershed,according to this study. Such data could be valuable in predicting future floods and
Degree Name
Doctor of Philosophy
Degree Level
Doctoral degree
Degree Department
Faculty of Engineering
Degree Discipline
Environmental and Water Resources Engineering
Degree Grantor(s)
Mahidol University