Assessment on the environmental vulnerability through the climate indexes of Dong Nai river basin

185 HNUE JOURNAL OF SCIENCE DOI: 10.18173/2354-1059.2018-0044 Natural Sciences 2018, Volume 63, Issue 6, pp. 185-190 This paper is available online at ASSESSMENT ON THE ENVIRONMENTAL VULNERABILITY THROUGH THE CLIMATE INDEXES OF DONG NAI RIVER BASIN Vu Thi Hang Faculty of Geography, Hanoi National University of Education Abstract. The author of the article uses EVI method for 4 indexes in the climate group of the sustainable development index to assess the vulnerability in 3 meteorological stations of Dong Nai river basin. Results show that the indexes of hot periods, cold periods and dry periods remain within safe limits when the vulnerability level is very low at level 1, but the wet periods are more vulnerable at level 3.These indexes have a very close relationship to the water source of river basin, so the results of the study will help policy makers and water users consider and decide on the water use in the future to ensure the sustainability of the water resource. Keywords: Dong Nai river basin, Environmental vulnerability index. 1. Introduction In the face of challenges to the promotion of economic growth in developing countries in recent years, many problems have arisen in terms of environment, society and the sustainability of the economic development pace. Many countries in the world, including Vietnam, have taken concrete steps to re-assess the indexes affecting the sustainable development of the country. In the overall development planning of a country, the planning on the sustainable development of large river basins is inevitable. Therefore, the research and assessment of river basin is very important for the sustainable use and exploitation of the basin's resources. In Vietnam, there are also many studies on the river basin environment, however, these studies mainly contain the separate assessment of each environmental component or the combined assessment with the need assessment of each type of resource. The assessment on the environmental vulnerability has been studied in many regions and countries around the world based on the perspective of the sustainable development with natural environment and socio-economic indexes. The environmental vulnerability index was developed by the South Pacific Applied Geoscience (SOPAC) and the United Nations Environment Program (UNEP) through a team of industry experts from different countries around the world. There are 50 vulnerability indexes covering the economic, social and environmental dimensions of the three pillars of the sustainable development. Depending on the characteristics and purposes of each country’s assessment, it is possible to use all the 50 indexes or less. Many countries in the world have considered EVI as a comprehensive environmental assessment tool for the future sustainable development orientations as United Kingdom, Japan, India, Bangladesh and Denmark. Received July 5, 2018. Revised July 19, 2018. Accepted July 26, 2018. Contact Vu Thi Hang, e-mail address: hangvuth76@gmail.com Vu Thi Hang 186 According to the assessment on the global environment [1], Vietnam is one of the countries where the environment is highly vulnerable. Nonetheless, in Viet Nam, there have not been many assessments on the environment vulnerability by region, river basin, province or city. Bac Kan [2] is one of the few provinces which have effectively used EVI to assess the environment in order to find out solutions for development in the future. Dong Nai river basin is one of the three major river basins in Vietnam, after the Mekong and Red River basins, including the provinces of Dak Nong, Lam Dong, Binh Phuoc, Binh Duong, Dong Nai, Tay Ninh, Ho Chi Minh City and a part of Binh Thuan and Long An with 37,400 km 2 in the territory of Vietnam [3]. The Dong Nai river system consists of the main Dong Nai river and four large tributaries, namely La Nga river on the left bank, Be river, Sai Gon river and Vam Co river on the right bank [4]. Dong Nai river basin is one of the river basins that is under pressure from economic development activities and is one of the hotspots that are sensitive to environmental impacts in general and the water environment in particular. In this study, the author uses 4 climate indexes (hot periods, cold periods, wet periods and dry periods), which are 4 out of the 50 environmental vulnerability indexes which are determined by international scientific organizations to assess the vulnerability in Dong Nai river basin because climate indexes have a very close relation to the water resource of the basin. These climate indexes have a great influence on the water flow and the evaporation process of the water resource in the river basin. Thus, the vulnerability assessment of these four indexes helps improve the planning and the use of water resources in a better and more sustainable way. 2. Content 2.1. Methods 2.1.1. Data collection and processing method The data collection and processing method is essential for the implementation of the studies on the environmental vulnerability assessments. The data and figures used in this study are cited from reliable sources, collected from prestigious research and monitoring institutions. This method is implemented in door, as well as on the field. The input data for the EVI method have very high requirements for consecutive climate data series for 30 years. Based on the data collected for the research territory, we selected the type of data to ensure the time consistency. The meteorological stations process data with the support of computer software such as Excel, etc. to have the standard data set for the calculation of climatic parameters for Dong Nai river basin. 2.1.2. Map - chart method The map - chart method is one of the most popular methods used in geography research in general and the physical geography in particular. This method is based on the recording, description, data analysis and synthesis of related phenomena to set up charts, graphs and maps to show the desired results. The calculation results of the data series in the study are showed in diagrams, which make it possible to compare the changes over time in different places, more clearly and visually - it is the best method to present the input data. The map - chart method in this study is the linkage between the 30-year data series of climate indexes in Dong Nai river basin with the results showed in a more intuitive and lively manner. 2.1.3. EVI assessment method There are many environmental assessment methods. In this study, we use the vulnerability assessment method for climatic indexes for Dong Nai river basin in accordance with the environmental vulnerability index (EVI) set [1]. The world has applied from 4 to 260 indexes to assess the vulnerability of the environment to quantify the sustainable development issues. However, EVI is a smart indicator with 50 indexes Assessment on the environmental vulnerability through the climate indexes of Dong Nai river basin 187 and is one of the first tools to effectively manage the environment. The 50 EVI indexes to measure the vulnerability used in studies in areas such as Climate Change, Biodiversity, Water, Agriculture, Health, Desertification, etc. They are quantified by analyzing the many-year data series. When using temperature-related indexes to assess the vulnerability of the environment, it is required to study the root cause of changes in the temperature in the upward or downward trend, and the finding of the root cause will help “diagnose” correctly and figure out the best solution. For this study, we only assess 4 EVI indexes related to the climate of Dong Nai river basin for 30 consecutive years, especially in using more detailed 5-year data to find out the increase or decrease to determine the vulnerability. The climate indexes in the river basin assessed by the EVI will be the basis for finding a link with the water source, which will better orientate water use in the socio-economic development process of the basin. 2.2. Data collection To assess the vulnerability of the climate indexes (hot periods, cold periods, dry periods and wet periods) in Dong Nai river basin, we use the 30-year data from 1986 to 2015 of three meteorological stations: Da Lat, Bao Loc and Tay Ninh (data provided by the National Meteorological and Hydrological Center). The input data for the calculation must be 30 years in a row; as a result, the selection of many meteorological stations in Dong Nai river basin is extremely difficult due to the historical factors or the unoccasional observation at some stations; therefore, only 3 meteorological stations, namely Da Lat, Bao Loc and Tay Ninh in Dong Nai river basin meet the input requirements of the EVI assessment. We use the following inputs: - Monthly rainfall of 30 years; - Monthly maximum temperature of 30 years; - Monthly minimum temperature of 30 years. 2.3. Results 2.3.1. Hot periods Hot periods are average annual excess heat (degrees) over the past 5 years for all days more than 5°C (9˚F) hotter than the 30-year mean monthly maximum, averaged over all reference climate stations [1]. Calculate average monthly maximum temperature of 30 years (1986 - 2015). - Calculate the number of excess days in the last 5 years (2011 - 2015) (T day max > T monthly max average + 5 o C). - Calculate the total hot excess in the last 5 years (2011 - 2015). - Hot periods = total hot excess / number of excess days. The study of hot periods over a long time helps us understand the change of temperature increases or decreases in the specific short cycle of each period or the whole study period. We calculate the index number of excess days in the last 5 years of the study cycle against the average temperature value to find the abnormal changes so as to figure out the root cause of the change. The root cause of rising and falling temperatures is due to human impacts on physical geography components which result in the changes in surface water and vegetation coverage. Table 1. Limit value of vulnerability for hot periods EVI 1 2 3 4 5 6 7 Hot ≤ 3.5 3.5 6 To determine the vulnerability level, we use the formula for calculating the converted value from the original data and comparing it to the EVI limit value. Transform used: LN (X+1) Vu Thi Hang 188 Table 2. Vulnerability of hot periods index in Dong Nai river basin Station Raw value Transformed value EVI Tay Ninh 41 3.7 2 Da Lat 0 0 1 Bao Loc 0 0 1 2.3.2. Cold periods Cold periods average annual heat deficit (degrees) over the past 5 years for all days more than 5 °C cooler than the 30 year mean monthly minimum, averaged over all reference climate stations [1]. - Calculate the average monthly minimum temperature of 30 years (1986 - 2015). - Calculate the number of heat deficit days in the last 5 years (2011 - 2015). - Calculate the total heat deficit in the last 5 years (2011 - 2015). - Cold periods = total number of heat deficit / number of heat deficit days). The vulnerability of the cold periods defines the days when the temperature drops to low level, resulting in the heat deficit, which greatly affects to water resource, temperature stress and crop yield and reduces the contamination level. This index not only indicates the days of lower temperature, but also the total number of heat deficit days. Table 3. Limit value of vulnerability for cold periods EVI 1 2 3 4 5 6 7 Cold ≤ 3.5 3.5 6 Transform used: LN (X+1) Table 4. Vulnerability of cold periods index in Dong Nai river basin Station Raw value Transformed value EVI Tay Ninh 0 0 1 Da Lat 0 0 1 Bao Loc 0 0 1 2.3.3. Wet periods Wet periods are average annual excess rainfall (mm) over the past 5 years for all months with > 20% higher rainfall than the 30 year monthly average, averaged over all reference climate stations [3]. - Calculate the average monthly rainfall of 30 years (1986 - 2015). - Calculate the number of excess months in the last 5 years (2011 - 2015). - Calculate the total rainfall excess in the last 5 years (2011 - 2015). - Wet periods = total rainfall excess / number of excess months. Table 5. Limit value of vulnerability for wet periods EVI 1 2 3 4 5 6 7 Wet ≤ 5 5 15 Transform used: sqrt (X). Issues related to floods, cyclones, wet periods, vegetation coverage of the ecosystem affect the changes in the water reserves. These indexes not only calculate the average of the 30 year rainfall, but also determine the total number of excess months. Assessment on the environmental vulnerability through the climate indexes of Dong Nai river basin 189 Table 6. Vulnerability of wet periods index in Dong Nai river basin Station Raw value Transformed value EVI Tay Ninh 60.4 7.8 3 Da Lat 56.8 7.5 3 Bao Loc 69.6 8.3 3 2.3.4. Dry periods Dry periods are average annual rainfall deficit (mm) over the past 5 years for all months with > 20% lower rainfall than the 30 year monthly average, averaged over all reference climate stations [1]. - Calculate the average monthly rainfall of 30 years (1986 - 2015). - Calculate the number of rainfall deficit months in the last 5 years (2011 - 2015). - Calculate the total rainfall deficit in the last 5 years (2011 - 2015). - Dry periods = total rainfall deficit / number of deficit months. The determination of the dry periods helps analyze factors affecting water supply and water retention, which may be due to nature or due to the human economic development activities. In two different regions, there is the same total volume of many-year rainfall, but the water deficiency in the last 5 years of the assessment cycle may be different for many causes. Table 7. Limit value of vulnerability for dry periods EVI 1 2 3 4 5 6 7 Dry ≤ 4 4 6.5 Transform used: Absolute value, LN (X) Table 8. Vulnerability of dry periods index in Dong Nai river basin Station Raw value Transformed value EVI Tay Ninh 21.8 3.1 1 Da Lat 29.3 3.4 1 Bao Loc 50.6 3.9 1 2.3.5. Environmental vulnerability assessment through the climate indexes of Dong Nai river basin Based on the calculation and analysis of the 30-years climate data series of Dong Nai river basin, we have identified the vulnerability as showed in Table 9. Table 9. Environmental vulnerability level through the climate indexes of Dong Nai river basin Station Wet Dry Hot Cold Tay Ninh 3 1 2 1 Da Lat 3 1 1 1 Bao Loc 3 1 1 1 Dong Nai river basin is located in a humid tropical climate receiving southwest monsoon and high rainfall, with two distinct seasons - dry season and rainy season. Due to the mild climate in Dong Nai river basin, all the results from all the three stations show that the dry periods and cold periods have a very low vulnerability level (level 1) due to the stable temperature range between the seasons, with little changes. Tay Ninh station has hot periods index at level 2 because it is located in the western part so the temperature is higher than the highland area and east of the river basin. Vu Thi Hang 190 Figure 1. Environmental vulnerability of the climatic indexes of Dong Nai river basin However, the wet index is more vulnerable, with all three stations at level 3 - medium vulnerability. Dong Nai river basin has a dense network of rivers, but they are unevenly distributed, with high rainfall during the rainy season, resulting in months with excessive water and mainly in the rainy season. Therefore, if the coverage is not good, it will lead to the phenomenon of not accumulating water for rivers, but also resulting in other environmental disasters, especially in the upstream area of Dong Nai river basin. The assessment results are showed in Figure 1. 3. Conclusion The climate characteristics have a great influence on the hydrological and water environment, so the assessment on the vulnerability of climate indexes is very important in assessing river basin water resources. The assessment on four climate indexes for three meteorological stations in Dong Nai river basin shows that the indexes of hot periods, cold periods and dry periods remain within safe limits when the vulnerability level is very low at level 1, but the wet periods are more vulnerable at level 3. Despite having not been at the highest level of warning, this assessment results also allow policy makers and water users to make plan on mitigating the vulnerability to be able to use water more sustainably in the future. REFERENCES [1] UNEP, 2015. Building resillience in SIDs:EVI [2] Geoffrey D. Gooch, Susan Baggett, 2011. Recommendations for strategies, conflict reconciliation, policy formulation and implementation [3] Tran Thanh Xuan, 2012. Water resources of main river systems in Vietnam. Education Publishing House. [4] Southern Institute for Water Resources Planning, 2005. Development and protection planning of water resources in Dong Nai river basin (in Vietnamese).