THE MEKONG FUTURE PROJECT FIRST DRAFT REPORT ON THE HYDROLOGICAL SIMULATION To Quang Toan 1, Nguyen Hieu Trung 2, Dang Kieu Nhan 3

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1 THE MEKONG FUTURE PROJECT FIRST DRAFT REPORT ON THE HYDROLOGICAL SIMULATION To Quang Toan 1, Nguyen Hieu Trung 2, Dang Kieu Nhan 3 1 Southern Institute of Water Resources Research, 2 Research Institute for Climate Change, Can Tho University, 3 Mekong Delta Research Institute, Can Tho University. Executive Summary This study aims to analyse how successful investments in water infrastructure in response to sealevel rise are. The study emphasizes the need to put such adaptation strategies into the larger context of land use change and upstream developments. In particular upstream developments such as hydropower, irrigation and water diversion can substantially offset the effect of hard adaptation measures such as dikes and sluice gates. Most importantly, the results emphasise the need to understand combined effects, such as the combination of sea-level rise, upstream dams, upstream irrigation and drought. Adding climate predictions (i.e. more dry years) into the equations suggests that negotiating how upstream dams are operated can have much larger effects than expensive investments in water infrastructure. I. Model description This report documents the hydrological analysis of relevant scenarios for Vietnam s Mekong Delta. The underlying model is based on an existing model developed by the Southern Institute for Water Resources Research (SIWRR). The new scenarios were developed by stakeholders as part of the Exploring Mekong Region Future project. I.1. Description of hydraulic schematization The hydraulic schematization starts from Kratie, it covers the floodplain in Cambodia and the whole Mekong Delta of Vietnam, so called as the simulated area. Within the simulated area, all rivers and canal networks were numbered to the scheme as well as the hydraulic work and land use and other water use (figure 1). The outside simulated areas in the Mekong River (upstream of Kratie) and Saigon Dongnai river basins (upstream of Tri An hydropower station) were selected as boundary conditions for the model.

2 Figure 1 The simulated schematization (Nguyen Quang Kim and To Quang Toan et al, 2010; Nguyen Sinh Huy, To Quang Toan et al, 2010) I.1.1 Physical condition: The physical conditions of rivers and canal systems and the hydraulic constructions used in this model are based on the conditions of the historically driest year of the Vietnamese Mekong Delta (VMD), year The operation of these constructions can be changed for number of water management scenarios. I.1.2 Upstream boundary conditions: Kratie flow was taken as the discharge boundary of the model. The observed flow at Kratie is used to calibrate the present condition of the simulated year. The simulated water flow at Kratie according to the future development condition is used to predict the future condition of the hydraulic infrastructure and the water quality conditions of the Mekong Delta. Besides, the flow of the Tonle Sap and other tributaries in Cambodia, downstream of Kratie, and the flow from Sai Gon Dong Nai river basin are also included as model boundaries. For this study, the upstream boundary will be based on the results of the recent national study on the impact of upstream development to VMD (figure 2)

3 I.1.3 Lower boundary condition: Figure 2 Model boundary conditions (Nguyen Quang Kim et al, 2010) Lower boundary conditions include all tidal boundaries at the East Sea (South China Sea) and the West Sea (Gulf of Thailand). I.1.4 Within the simulated area Inside the simulated area (including the flood plain in Cambodia and VMD), all types of water use can be simulated: for agriculture, domestic, industrial development In addition, rainfall and evaporation, storage, and water logging are taken into account (figure 3).

4 Figure 3 Water in and out of the delta (Nguyen Quang Kim and To Quang Toan et al, 2010; Nguyen Sinh Huy, To Quang Toan et al, 2010) I.2. Scenarios The model simulations make for the Exploring Mekong Region Futures project different assumptions for sea level rise and upstream water regime changes over the next 40 years. In total 5 scenarios have been taken into account, as listed in Table 1. Table 1 Simulated Scenarios No Abbreviation Description SCN0: SLR30+RfC SCN1: SLR30+RfC+AgrP SCN2.1: SLR30 + UPS30 SCN2.2: SLR30 + UPS30-Qp85% SCN2.3: SLR30 + NFD-Opti SCN2.4: SLR30 + RVCNA SCN3: SCN1 + CloseW SCN4: SCN2 + CloseW SCN5: SCN4 + CloseAll Sea level rise 30cm + Rainfall pattern change (Climate change) + Based year land use Sea level rise 30cm + Rainfall pattern change + Land use scenario (toward increasing of rice area) SCN1 + Upstream hydropower and land use scenario. SCN1 + Upstream hydropower and land use scenario in the drought hydrological year with probability of 85% SCN1 + Upstream near future hydropower dams scenario with optimum operation (NFD-Opti) (based on Nguyen Quang Kim, et. al., 2010) SCN1 + Upstream hydropower and main stream dams in the RVCNA model (based on Hannu Lauri, 2011) SCN1 + Cailon and Caibe sluice gates (close two large river at the West Sea-Gulf of Thailand) + sea dikes SCN2.1 + Cailon and Caibe sluice gates (close two large river at the West Sea-Gulf of Thailand) + sea dikes SCN4 + Hamluong and Cochien sluice gates (close 2 main Mekong river mounts)

5 I.2.1 Sources of data and information from upstream Mekong River Basin (MRB) The data and information at the upstream MRB is updated from various sources, including data on meteorology and hydrology; data on land use and agriculture; data on hydropower development. The main source of data achieved from MRC programs as Water Utilization Program (WUP, ), Basin development Plan (BDP, ) and Hydropower Program (HP, ). The data were checked and supplemented by a variety of applications in the Mekong River Basin, e.g. the applications within MRC program such as WUP, BDP Phase 2; IKMP. Through national research projects, such as studies carried out by VNMC and concerned agencies, Research Institutes and Universities. The data on operational schedule of reservoirs and hydropower plants, most of the hydropower is on the feasibility study stage or on the designing stage, therefore the operation schedule information was not available or unofficial, except some information available for Ialy hydropower dam and some reservoirs in Thailand. The lack of reservoir operation schedule were estimated based on estimated inflow condition to the reservoirs, the installed capacity, the expected power production..., the operation schedule is established. The assumptions are given as: - 'Optimal dam operation': it was assumed that the hydropower plant will reduce the number of operated turbines in case of drought year to ensure continuous operation of the hydropower reservoirs, at least one unit. The advantage of this operation is to maintain the continuous increase of the downstream flow. However, the disadvantage of this type of operation is that it does not always operate at full generating capacity; - 'Operation based on power demand': this mode is driven by the power demand and means that even when water levels drop dam operators try to maintain the power output. While there is the aim to maintain a number of turbine units to operate at minimal productivity there is the risk that the whole hydropower plant has to shut down because the reservoir water level reaches the dead storage level. In such cases during dry years the ability to maintain continuous regulated high flow to downstream of reservoir is low. I.2.2 Some limitation and uncertain factors - There is a large number of hydropower dams and inconsistency of data and information as each future hydropower plant has a number of options to design and operate. This study cannot consider the full range of possible combinations of operational scenarios of upstream hydropower reservoirs. Instead the two extremes are assumed as outlined above (optimal operation and based on power demand) and combined with the available hydrologic data series from ; - The limitations coming with the use of simulation tools, including the use of the DSF model and the IQQM model, as not all required input data was available in particular regarding the operation of dams; - There are critical uncertainties regarding the inflow to existing and future reservoirs in particular due to the loss of forest area for hydropower development and due to resettlements and population growth. These factors suggest that the future inflow into reservoirs will change. Additionally, climate change is likely to introduce changes in precipitation levels and in climate variability. I.2.3 Consideration for upstream boundary condition - The dry season flow of the recent severely dry hydrological year was used for the simulation. The year 2005 was selected, which was considered as a drought year with substantial salinity intrusion in the Mekong delta (used in SCN0, SCN1, SCN3) ;

6 - Assuming similar flow conditions as in 2005, upstream development is modelled, in particularly the near future dams with 'operation based on the power demand' (SCN2.1, SCN4 and SCN5); - The model requires assumption regarding upstream flow, which involves several uncertainties, as mentioned above. These uncertain factors include, for instance the forest area and climate change conditions. However, this report considers flow data based on the flow frequency analysis of a series of hydrologic data to Kratie from 1924 to present, corresponding to 85% flow frequency (a return period of about 7 year / time). In addition to the actual flow assumption, a scenario for reduced flow in the near future dams scenario was considered in combination with the assumption 'operation based on power demand' (SCN 2.2) - The assumption on upstream flow in the near future dams scenario with 'optimum operation' considered increased flow similar to 1988 ( SCN 2.3) - Upstream flow is considered to be affected by additional hydropower development in scenario SCN2.4. This scenario assumes 126 dams, which exceeds the near future dam assumption and includes mainstream hydropower in the LMB and takes into account climate change. These assumptions on flow and climate change are based on 'lowest flow' in 2038 in the RVCNA scenario done by Hannu. I.2.4 Description of input data to for scenarios Physical condition (water management constructions): The physical conditions of the baseline simulated year (2005) is used for SCN0 and SCN1; upstream development will be added to SCN2; Cailon and Caibe sluice gates at the two main rivers at the West Sea (Gulf of Thailand) and sea dike (Nguyen Ngoc Anh, 2010 and annex 4 ) will be included into SCN3 and SCN4; the Hamluong and Cochien sluice gates at the two Mekong river s mouths will be included in SCN5 (table 2). Table 2: Description of basic physical changes in simulated scenarios No Physical change Description of the change 1 SCN : Upstream development (see table 3) - 8 Chinese dams - in addition, 36 Lower Mekong Basin dams (except the lower mainstream dams, as they are considered as the run-of-river hydropower - impact mainly to the silt deposit and to the flow by type of 2 SCN2.4: Upstream development including mainstream dams 3 SCN3 and SCN4: Cailon and Caibe sluice gates 4 SCN5: Cailon, Caibe, Hamluong and Cochien sluices operation) Obtained the results from Hannu Lauri, EIA Ltd. 2011, including 126 reservoirs in Mekong river basin, in which 6 mainstream dams from China and 10 mainstream dams in lower Mekong basin (see Table 4) Dimension of each sluice is assumed as 80% of the width of the river s cross-section (similar to the other sluices in the VMD). Dimension of each sluice is assumed as 80% of the width of the river s cross-section.

7 Table 3: List of simulated hydropower dams in the near future condition (Sources: Nguyen Quang Kim and To Quang Toan et al, 2010; MRC/BDP, 2010a,b; MRC/BDP-phase2, 2009; MRC, 2008; MRC, 2009; MRC, 2010a,b,c,d) No Hydropower dams Country Active volume (10 6 m 3 ) Installed capacity (MW) 1 Gonggouqiao Dam CN Xiaowan dam CN 9, Manwan dam CN Dachaoshan dam CN Nuozhadu dam CN 12, Jinghong dam CN Nam Ngum Dam L N Theun- Hin Boun Dam L Nam Leuk Dam L Houay Ho Dam L Nam Song diversion weir L Nam Ngum 2 dam L NamThuen2 Dam L XeSet2 Dam L Xekaman3 Dam L Xekaman1 Dam L Nam Ngum 5 Dam L Nam Mang3 L Xekaman2 Dam L NamLik2 Dam L Lam Ta Kong Dam T Ubol Ratana Dam T Lam Pao Dam T Sirindhorn Dam T Pak Mun Dam T Nam Un Dam T Nam Pung Dam T Chulabhorn Dam T Lam Phra Pleng Dam T Huai Luang Dam T Lam Nang Rong Dam T Upper Mun Reservoir T Ya Li Dam V Plei Krong Dam V SeSan3 Dam V SeSan3A Dam V Tourash Dam V BuonKop Dam V Srepok3 Dam V Srepok4 Dam V Sesan4 Dam V Sesan4A-Res V Notes: CN: China; L: Lao PDR; T: Thailand; V: Vietnam

8 Table 4: Reservoirs in different countries simulated by Vmod model (Hannu Lauri, 2011) Country number of reservoirs active storage (10 6 m 3 ) in mainstream active storage (10 6 m 3 ) China Lao PDR Cambodia Thailand Vietnam sum Upstream boundary conditions: Observed discharge at Kratie during the dry year 2005 is used for SCN0, SCN1 and SCN3. Future upstream development (hydropower development and agriculture development) is included in SCN2.1, SCN4 and SCN5 (table 5). Table 5: Description of hydropower and irrigation at upstream was taken into account in the model (Nguyen Quang Kim and To Quang Toan et. al., 2010) No Situation Abbreviation 1 2 Existing and near future hydropower development High agriculture development scenario NFD Irrigation area (1000 ha) 3,400 (existing) HAD 6,620 Active storage volume of simulated reservoirs (10 6 m 3 ) Lower Mekong Basin dams China dams 26,230 22,700 In high agriculture development scenario (HAD), it is assumed that the area under agriculture doubles in Thailand, Lao and Cambodia. With this assumption and based on the hydrological condition from 1985 to 2000, the flow to Kratie would decrease during the dry season by about 180 m 3 /s to 600 m 3 /s. In combination with the Near Future Hydropower Development scenario (NFD+HAD), with the same hydrological condition from 1985 to 2000, the monthly flow to Kratie is likely to change as shown in Table 6. Table 6: Estimated change of discharge at Kratie in the High Agriculture Development scenario (HAD) and the HAD in combination with Near Future Hydropower scenario (HAD-NFD) (based on Nguyen Quang Kim and To Quang Toan et. al., 2010) HAD HAD+NFD

9 Based on the calculated changes in discharge due to upstream development scenarios, the 2005 flow conditions can be re-estimated with 85% probability (figure 4) (Decision 1590/QD-TTg of the Price Minster). In addition, to cover the whole possibility and uncertainty for the Mekong river future hydrology condition, SCN2.3 was added with the near future dams with optimum operation of dams for hydropower generation and regulation of water (see detail data analysis in appendix 1.5). SCN2.4 was added with the future dams and the climate condition (CNA) and with optimum operation of dams (see detail data analysis in appendix 1.3 and 1.4). Figure 4: Kratie boundary condition for simulated scenarios Notes: Q2005: flow at Kratie in 2005; Q2005+upsdvl: flow at Kratie with the impact of upstream development scenario (Q2005+Q HAD_NFD); Q85%: flow at Kratie with probability of 85%; Qp85%+upsdvl: flow at Kratie with probability of 85% with the impact of upstream development scenario (Qp85% + Q HAD-NFD); NFD_Opti_88:flow at Kratie in near future dams scenarios with optimum operation of dams, min flow taken from hydrological year 1988 based on the flow period from ; CC_RVCNA_2038: flow at Kratie based on Hannu (2011) in the future dams scenario with climate change condition (RVCNA), min flow taken in 2038 based on the projected flow of the period from Lower boundary condition: Additionally, a sea level rise of 30cm (projection to the period of of MONRE, 2009) was added for all lower boundaries (river mouths). The sea level rise was taken from the recent Ministry level study for the Scientific base to Adapt to the Climate Change and Sea Level Rise in the Mekong Delta (Nguyen Sinh Huy and To Quang Toan et al, 2010). According to this study, the spring tidal may increase faster in the East Sea and the leap tidal may increase faster in the West Sea.

10 Table 7: The spring and leap tidal variation change in East and West sea (Nguyen Sinh Huy and To Quang Toan et al, 2010) Station Season γ peak γ low Vung Tau (East Sea) Xeo Ro (West Sea) Dry Flood Dry Flood Figure 5: Tidal boundary condition at My Thanh station on 2005 and SLR 30 cm (Nguyen Sinh Huy and To Quang Toan et al, 2010) Figure 6: Tidal boundary condition at Xeo Ro station on 2005 and SLR 30 cm (Nguyen Sinh Huy and To Quang Toan et al, 2010)

11 Inside of the VMD: The delta is divided into 120 zones, which is based on the physical, topography and administrative boundaries. Each zone has a detailed crop area and crop calendar, climate condition of 2050 was projected based on the national projection for climate change scenarios. A new schematization for water demand was developed for this study as was given in table 8. Figure 7: Irrigation water demand model for the Mekong delta

12 Table 8: Rice crop area by Provinces for the baseline year (2005) (Nguyen Quang Kim and To Quang Toan et al, 2010; Nguyen Sinh Huy and To Quang Toan et al, 2010) Rice crop area (1000 ha) Provinces Summer Autumn Winter Spring Autumn Winter Main Rice Long An Dong Thap An Giang Tien Giang Vinh Long Ben Tre Kien Giang Can Tho Hau giang Tra Vinh Soc Trang Bac Lieu Ca Mau II. Results and discussions. The model outputs are the monthly salinity levels and duration maps for the five simulated scenarios. The maps are in raster format (grid) with cell side of 200m. All maps are in GIS format that can be open by ArcGIS or ArcView software. For assessing agricultural and water supply impacts 4g/l isohalines are delineated. The water demand of the base year land use (2005) and the land use scenario are also estimated and presented in Annex 1. Discharge, water level, and salinity level of critical locations in the VMD are presented in the annexes 2 and 3 for the proposed scenarios. The following analysis focuses on the implications of additional agricultural development in the VMD under the projected hydrological changes. II. 1. The impacts of intensifying rice cultivation on the salinity intrusion in the VMD Comparing the salinity intrusion maps of SCN0 (sea level rise of 30cm and reduced rainfall) and the SCN1 (SCN0 + increased area under rice in upstream VMD provinces), salinity levels of 2g/l are projected to increase only in the Quang Lo Phung Hiep salinity control project (Soc Trang and Bac Lieu provinces) (figure 8). However, the area with salinity level higher than 4g/l are not significantly extended (figure 9a). This implies that the intensification of rice production at the upstream provinces of the VMD will not affect very much salinity in downstream provinces during the dry season.

13 a. Maximum saline intrusion from Jan to April in SCN0 b. Maximum saline intrusion from Jan to April in SCN1 Sea level rise 30cm + Rainfall pattern change (Climate change) + Based year land use SCN0 + rice intensification (food security) Figure 8: Maximum saline intrusion in the based scenario and scenario 1. a. Change on salinity intrusion area of 4g/l Jan to April in SCN1-SCN0 b. Change on salinity intrusion area of 1-4g/l Jan to April in SCN1-SCN0 - Fresh water means the salinity concentration <1g/l - Brackish water condition = salinity concentration varies from 1g/l to 4g/l - Salty condition means the salinity concentration is higher than 4g/l Figure 9: Change on salinity intrusion between SCN1 and SCN0 II. 2. The impacts of the upstream hydropower on the salinity intrusion in the VMD The salinity maps of SCN1 (figure 8b) and SCN2.1 (figure 10a) show that under base year conditions (2005) upstream hydropower development as specified for SCN2.1 will not impact salinity intrusion in the VMD years with normal precipitation. However, during a dry year (85% probability drought or return period of 7 years) significant increase in salinity levels and of saline duration will be observed in large areas of the Mekong Delta (figure 10b and 11b). Especially in the Bassac branch of the Mekong River, salinity is projected to intrude Can Tho city and strongly impact on the Quan Lo Phung Hiep and Nam Mang Thit salinity control projects. The other area that is projected to have higher salinity level is the Ben Tre province.

14 a. Maximum saline intrusion from Jan to April in SCN2.1-Q05 b. Maximum saline intrusion from Jan to April in SCN2.2-Qp85% SCN1 + Upstream hydropower and rice intensification SCN2-Q05 + drought hydrological year with probability of 85% c. Maximum saline intrusion from Jan to April in SCN2.3 d. Maximum saline intrusion from Jan to April in SCN2.4 Figure 10: Maximum saline intrusion in scenarios 2.1, and 2.4 Figures 11c shows that the highly certain near future hydropower development projects will increase salt water (>4g/l) in a few small areas of the coastal VMD if we assume optimal dam operation. Other small areas turn from salt water area (>4g/) into brackish water (Figures 11c and 11d). This implies that in case of optimum operation of the upstream dams (both highly certain near future dams, SCN2.3, and uncertain hydropower development, SCN2.4), there is little impacts to the salinity intrusion of the VMD). However, in case of dry year (Figure 11b) without optimum dams operation (SCN2.2), large area of the VMD (> 274,000ha) will be under saline condition.

15 a. Change on salinity intrusion area of 4g/l Jan to April in SCN21-SCN1 b. Change on salinity intrusion area of 4g/l Jan to April in SCN22-SCN1 c. Change on salinity intrusion area of 4g/l Jan to April in SCN23-SCN1 d. Change on salinity intrusion area of 4g/l Jan to April in SCN24-SCN1 Figure 11: Change on salinity intrusion between SCN2.1, SCN2.2, SCN2.3 and SCN2.4 with SCN1

16 a. Change on salinity intrusion area of 1-4g/l Jan to April in SCN2.1-SCN1 b. Change on salinity intrusion area of 1-4g/l Jan to April in SCN2.2-SCN1 c. Change on salinity intrusion area of 1-4g/l Jan to April in SCN2.3-SCN1 d. Change on salinity intrusion area of 1-4g/l Jan to April in SCN2.4-SCN1 Figure 12: Change on salinity intrusion with brakish water between SCN2.1, SCN2.2, SCN2.3 and SCN2.4 with SCN1 II. 3. The effectiveness of the VMD's sluices solution Figure show the effectiveness of the proposed structural measures to control salinity in the Mekong Delta. In SCN3 and 4 the Cai Lon and Cai Be sluices are assumed to operate, protecting effectively large areas in Provinces of Ca Mau and Bac Lieu from saline intrusion (Figure 13a and 13b). Tables 9 and 10 present the gain and loss of fresh and salt water area if the analyzed scenarios. With Cai Lon and Cai Be sluices, there would be 133,000 ha of Ca Mau and Kien Giang province change from salt to fresh water area. a) Maximum saline intrusion from Jan to April in SCN3 b) Maximum saline intrusion from Jan to April in SCN4 SCN1 + Cailon and Caibe sluice gates + sea dikes SCN2 + Cailon and Caibe sluice gates + sea dikes Figure 13: Maximum saline intrusion in scenarios 3 and 4

17 a. Change on salinity intrusion area of 4g/l Jan to April in SCN3-SCN1 b. Change on salinity intrusion area of 4g/l Jan to April in SCN4-SCN1 Figure 14: Change on salinity intrusion between SCN3 and SCN4 with SCN1 a. Change on salinity intrusion area of 1-4g/l Jan to April in SCN3-SCN1 b. Change on salinity intrusion area of 1-4g/l Jan to April in SCN4-SCN1 Figure 15 : Change on salinity intrusion with brackish water between SCN3 and SCN4 with SCN1 Figures 16 and 17 show that the proposed sluices (Cai Lon, Cai Be, Cochien and Hamluong) would significantly reduce the salinity condition of the Mekong branch and therefore reduce the level of salinity in parts of Ca Mau, Kien Giang, Hau Giang, Tra Vinh, and Ben Tre province (273,000ha, see table 9 and 10). However, since the Bassac branch will not be closed, the remaining area close to the Bassac river of Tra Vinh and parts of Soc Trang and Bac Lieu province is projected to be under high salinity level. It should be noted that this model only simulated the salinity intrusion of the VMD under the proposed major sluice gates. Enclosing of the VMD can cause serious environment problems such as acidity from acid sulphate soils, water pollution from domestic and industrial waste water. Therefore, a detailed environment impact assessment should be performed in future research.

18 Figure 22: Maximum saline intrusion from Jan to April in SCN5 SCN4 + Hamluong and Cochien sluice gates Figure 16: Maximum saline intrusion in scenario 5 a. Change on salinity intrusion area of 4g/l Jan to April in SCN5-SCN0 b. Change on salinity intrusion area of 1-4g/l Jan to April in SCN5-SCN0 Figure 17: Change on salinity intrusion between SCN5 and SCN0 Table 9: Calculated the affected area by salinity intrusion in the Mekong delta of Vietnam (1000 ha) No Salinity condition SCN0 SCN1 SCN21 SCN22 SCN23 SCN24 SCN3 SCN4 SCN5 1 Fresh water < 2 g/l g/l g/l g/l >20 g/l Impacts on rice area (>4g/l) No Salinity condition SCN0 SCN1 SCN21 SCN22 SCN23 SCN24 SCN3 SCN4 SCN5 1 Fresh water or protected <4gl >4gl

19 Table 10: Salinity intrusion of simulated scenarios compare with baseline SCN0 and SCN1(1000 ha) SCN1- SCN21- SCN22- SCN23 SCN24 SCN3- SCN4- SCN5- No Salinity condition SCN0 SCN1 SCN1 - SCN1 - SCN1 SCN1 SCN1 SCN1 No 1 1 Fresh water < 2 g/l g/l g/l g/l >20 g/l Impacts on rice area (>4g/l) Salinity condition SCN1- SCN0 SCN21- SCN1 SCN22- SCN1 SCN23 - SCN1 SCN24 - SCN1 SCN3- SCN1 SCN4- SCN1 SCN5- SCN1 Fresh water or protected <4gl >4gl Note: (-) minus value means decreasing area, opposite means increasing area Table 11: Comparison of salinity intrusion of simulated scenarios with SCN2.2 Unit: 1000 ha No Salinity condition SCN2.4- SCN2.2 SCN3- SCN2.2 SCN4 - SCN2.2 SCN5- SCN2.2 1 fresh water or protected < 2 g/l g/l g/l g/l >20 g/l Clarify for rice cultivation condition (4g/l) No Salinity condition SCN1 - SCN0 SCN21- SCN1 SCN22 - SCN1 SCN23 - SCN1 1 fresh water or protected <4gl >4gl Note: (-) minus value means decreasing area, opposite means increasing area Table 12: Salinity intrusion of simulated scenarios compare with baseline SCN0 and SCN1(1000 ha) N o Salinity condition SCN1- SCN0 SCN21- SCN1 SCN22- SCN1 SCN23 - SCN1 SCN24 - SCN1 SCN3- SCN1 SCN4- SCN1 SCN5- SCN1 1 Brackish turn to fresh Salty turn to fresh Salty turn to brackish Fresh turn to brackish Brackish turn to salty Improving Worsen Note: - Fresh water means the salinity concentration <1g/l

20 - Brackish water condition means the salinity concentration varies from 1g/l to 4g/l - Salty condition means the salinity concentration is higher than 4g/l Table 13: Summary the impact of salinity intrusion change in simulated scenarios for rice cultivation (compare with baseline SCN0 and SCN1(ha) N o Salinity condition SCN1- SCN0 SCN21- SCN1 SCN22- SCN1 SCN23- SCN1 SCN24- SCN1 SCN3- SCN1 SCN4- SCN1 SCN5- SCN1 Fresh turn to salty 14, brackish turn to salty 2,253 6,216 71,290 6, ,595 4,791 3,904 Fresh turn to brackish 7,606 19, ,135 26,138 6,436 9,940 15,509 5,367 Brackish turn to fresh ,078 63,465 24,609 7,568 55,366 Salty turn to brackish ,315 6,528 3,828 13,355 Salty turn to fresh 1,288 5,638 5,219 13,441 Fresh turn to salty 3,750 1,138 1,255 1,258 brackish turn to salty 7,165 3,020 32,891 2, , Fresh turn to brackish 16,107 23,103 75,053 22, ,742 1,386 Brackish turn to fresh ,339 41,439 21,351 16,922 62,379 Salty turn to brackish 73 1,503 15,834 9,867 9,009 12,007 Salty turn to fresh 18,004 17,323 37,572 Fresh turn to salty 40 1, ,014 1,038 brackish turn to salty 7,409 11,486 23,855 14,996 1,327 1,929 7,796 5,403 Fresh turn to brackish 2,099 5,946 11,848 6, , Brackish turn to fresh ,417 5, ,354 Salty turn to brackish ,717 15,052 5,902 16,190 Salty turn to fresh 15,868 15,444 15,320 Positive in 3 rice crop area ,673 78,780 36,775 16,614 82,162 Negative in 3 rice crop area 9,858 25, ,605 33,960 8,100 12,421 21,250 10,041 3-rice crop 2 rices (WS+SA) 2 rices (SA+M) Positive in 2 rices(ws+sa) ,842 57,273 49,222 43, ,95 9 Negative in 2 rices(ws+sa) 23,272 26, ,694 25,351 2,446 2,607 4,398 2,199 Positive in 2 rices(sa+m) ,134 36,355 21,489 39,864 Negative in 2 rices(sa+m) 9,508 17,432 35,743 22,691 3,115 3,731 10,295 5,668

21 a. Impact of salinity intrusion change to rice crop area in SCN2.1-SCN1 ba. Impact of salinity intrusion change to rice crop area in SCN2.2-SCN1 a. Impact of salinity intrusion change to rice crop area in SCN2.4-SCN1 ba. Impact of salinity intrusion change to rice crop area in SCN5-SCN1 Figure 18: Impact of salinity intrusion change on some selected scenario to rice crop area in comparison with SCN1 II.4 Implication for land use planning in the VMD under Climate Change, sea-level rise and upstream development projects Overlaying projected saline intrusion maps and proposed land use maps that aim for food security allows identifying areas under different land uses that would be affected by saline intrusion under the projected scenarios. This aims to support land use planning policy for the VMD and adaptation measures to climate change, sea level rise, and especially to the possible upstream development projects, which influence hydrological conditions of the Mekong River. Additionally, model results for water demand show that under climate change assumptions water demand increase significantly in the rice intensification scenario, during the early stage of Winter-Spring crop (December - February) and Summer - Autumn crop (May - June) (see Annex 1 Figure a2). This information is important for land use planners to specify suitable cropping calendars or suitable crops for adapting to changes in water availability.

22 Figure 18: Maximum salinity from Jan to April of simulated scenarios III. Summary The study applies hydrological modelling to examine different scenarios for understanding how the structural measures both upstream and in the Mekong Delta impact on agricultural production in the Mekong Delta given a sea level rise of 30cm (projected at 40 years from now). The study's results can be summarized as follows: The extending of rice area at the upper part of VMD can increase salinity levels in the coastal area of the VMD. A sea-level rise of 30cm and an increased area under rice in the upstream VMD impact about 90,000 ha fresh water land of the coastal provinces by saline water. This is equivalent to the loss of 120,000 ton of rice compared to the based scenario (SLR 30cm with land use 2005). Socio-economic and environmental impacts assessments should be carried out to inform the decision maker on the gain and loss of the large construction in the Mekong Delta. In terms of rice production, the model shows that the large sluice gates in the Delta can increase from 160,000 ton to 300,000 ton of rice compare to the based scenario. Upstream developments strongly impact on the Mekong Delta, especially after dry years and if dam operators try to maintain maximum power generation as long as possible. The model results show that under such assumptions in a situation of highly likely hydropower development (42 near future hydropower dams under low flow of 85% probability, ), serious saline intrusion can occur in the VMD leading to a loss of more than 1million tons of rice compare to the based scenario.

23 In case of optimal dam operation even all 126 upstream hydropower dams would improve hydrological conditions in the VMD, increasing rice production in the VMD by more than 300,000 tons if compared with the based scenario. This emphasizes the importance of collaboration among riparian countries on hydro-power operation and irrigation development projects to mitigate the negative impacts on the VMD. However, It is essential to have further study to examine the impacts of 126 upstream hydro-dams under non-optimum operation to the VMD in specific and the Mekong Basin in general.

24 REFERENCES 1. Decision 1590/QD-TTg dated 9 Oct 2009 of Prime Minister, Strategy for water resources development in Vietnam. Government of Vietnam. 2. ICEM, 2009, Inception Report: MRC SEA For Hydropower on the Mekong Mainstream, International Centre For Environmental Management. ICEM. 3. Nguyen Quang Kim, To Quang Toan, et. al., An investigation on the efficient use of water related to the upstream development scenarios to prevent drought and salinity intrusion in the Mekong delta National project KC08-11/ Hanoi Water Resources University (HWR) & Southern Institute of Water Resources Research (SIWRR). 4. Nguyen Sinh Huy, To Quang Toan, et. al., Scientific base for adaptation measures for climate change and sea water level rise to the Mekong delta; Ministry level project. Hanoi Water Resources University. 5. Nguyen Ngoc Anh, Water resources planning in the Mekong delta to adapt with climate change condition; Southern Institute for Water Resources Planning and projection (SIWRP). 6. MRC, 2003, State of the Basin Report. MRC Phnom Penh. 7. MRC, 2008a, An assessment of water quality in the Lower Mekong Basin. 8. MRC, 2008b, Fast Track Scenarios of Basin Development Plan (MRCS): Model Simulations Using DSF. 9. MRC, 2009a, IWRM-Based Basin Development Strategy for the Lower Mekong Basin. 10. MRC, 2009b, Economic, Environment and Socical Impact Assessment of Basin-wide Development Scenarios, 7 th Regional Technical Working Group Meeting papers. 11. MRC/BDP, 2010a. Evaluation of basin-wide development scenarios; MRC. 12. MRC/BDP, 2010b, Technical note 5, 8, 9, 10 and 11, evaluation the impact on water quality, salinity intrusion, wetlands, biodiversity, and aquatic lives. MRC. 13. MRC/BDP-phase2, 2009, Hydropower Sector review for the Joint Basin Planning Process. 14. MRC, 2010a, Evaluation of Basin-wide Development Scenarios, 9 th Regional Technical Working Group Meeting papers. 15. MRC, 2010b, Assessment of Basin-wide Development Scenarios, Technical report. 16. MRC, 2010c, Technical guideline for Guidelines for the Procedures for Maintenance of Flows on the Mainstream (PMFM), 8th Meeting of The Technical Review Group. 17. MRC, 2010d, State of the Basin Report, Vientiane, Lao PDR. 18. MRC, DSF, Decision Support Framework. 19. MONRE Vietnam National projection for Climate change. 20. Hannu Lauri, EIA Ltd., 2011, Vmod hydrological model MKF 5km reservoir scenario

25 ANNEX Water demand for land use 2005 in the present climate condition and CC in 2050 Figure a1: Summary of MD irrigation water demand in land-use 2005 with present climate condition and CC in Water demand for proposed land use planning in 2050 and climate change scenario in 2050 Table a1: Proposed land use planning in 2050 in MF scenario Provinces Proposed crop area (ha) W-S rice S-A rice A-W rice Main rice Dry crop An Giang 274, , ,498-22,941 Bạc Liêu 1,893 73,851 33,297 29, Bến Tre 37,541 50,292 36,549 13,164 - Cà Mau 33,245 16,692-86,526 - Cần Thơ 86,261 86,261 62,792 16, Đồng Tháp 257, ,788 64,585-36,266 Hậu Giang 87,396 87,396 46,478 1, Kiên Giang 282, , ,647 81,108 - Long An 254, ,644 47,057 41,161 23,396 Sóc Trăng 100, ,205 34,534 79,571 2,515 Tiền Giang 92,403 88,956 76,293 5, Trà Vinh 81,975 79,533 45,883 26,341 - Vĩnh Long 82,747 82,747 70, ,285 Total 1,733,310 1,791, , ,884 94,640

26 Figure a2: Summary of MD irrigation water demand in MF land-use planning with climate condition in The average of the the monthly average discharge to Kratie from (Data obtained from Hannu Lauri, EIA Ltd., 2011 and analysed by To Quang Toan) Table a2: average of monthly discharge from 2032 to 2055 at Kratie in climate change scenarios RVBL RVCCA RVCCB RVCNA RVCNB RVGIA RVGIB RVMPA RVMPB RVNCA RVNCB RVE Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average Remark: 1)RVCNA scenario was considered as the lowest discharge to Kratie among 12 climate scenarios; 2) red box means the discharge in simulated scenario is smaller then the discharge in baseline scenario (RVBL); 3) the lowest discharge in RVCNA within the period from 2032 to 2055 was fall in 2038.

27 1.4 The monthly discharge to Kratie in RVCNA scenario from (Analysing based on data obtained from Hannu Lauri, EIA Ltd., 2011) Table a3: monthly discharge at Kratie in RVCNA scenario from 2033 to Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average Remark: the projected hydrological data in the period of , discharge of Kratie in 2038 is smallest. 1.5 ly discharge at Kratie in optimum near future dams operation with based natural hydrological data from (based on data obtained from To Quang Toan and Nguyen Quang Kim, 2010 ) Table a4: monthly discharge to Kratie in optimun near future dams with hydrological data from 1986 to Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average

28 ANNEX Hydrological condition in SCN0 Table a5: Mean monthly inflow to Delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN0 Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average Table a6: Summary of max and mean monthly water level at some location in the Mekong delta in SCN0 Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average Hydrological condition in SCN1 Table a7: Mean monthly inflow to Delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN1 Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average

29 Table a8: Summary of max and mean monthly water level at some location in the Mekong delta in SCN1 Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average Hydrological condition in SCN2.1 with upstream flow as 2005 Table a9: Mean monthly inflow to Delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN2.1-Q05 Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average Table a10: Summary of max and mean monthly water level at some location in the Mekong delta in SCN2.1-Q05 Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average

30 2.4. Hydrological condition in SCN2.2 with upstream flow with probability of 85% and upstream development condition Table a11: Mean monthly inflow to delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN2.2-Qp85% Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average Table a12: Summary of max and mean monthly water level at some location in the Mekong delta in SCN2.2-Qp85% Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average Hydrological condition in SCN2.3 with near future dams and optimun dams operation Table a13: Mean monthly inflow to delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN2.3-NFD-Opti Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average

31 Table a14: Summary of max and mean monthly water level at some location in the Mekong delta in SCN2.3-NFD-opti Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average Hydrological condition in SCN2.4 with the future dams and cliamate change condition Table a15: Mean monthly inflow to delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN2.4-RVCNA-opti Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average Table a16: Summary of max and mean monthly water level at some location in the Mekong delta in SCN2.4-RVCNA-opti Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average

32 2.7. Hydrological condition in SCN3 Table a17: Mean monthly inflow to Delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN3 Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average Table a18: Summary of max and mean monthly water level at some location in the Mekong Delta in SCN3 Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average Hydrological condition in SCN4 Table a19: Mean monthly inflow to Delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN4 Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average

33 Table a20: Summary of max and mean monthly water level at some location in the Mekong delta in SCN4 Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average Hydrological condition in SCN5 Table a21: Mean monthly inflow to Delta at Tan Chau and Chau Doc and outflow to the sea via Mekong river mouths in SCN5 Inflow to Mekong delta (m 3 /s) Outflow to the sea via Mekong river mouths (m 3 /s) Total Tân Châu Total Tiểu Hàm Cổ Cung Định Trần in châu đốc out &Đại luông chiên hầu an đề Jan Feb Mar Apr May Jun Average Table a22: Summary of max and mean monthly water level at some location in the Mekong Delta in SCN5 Tân Châu Mỹ Cần Mỹ Sơn Bến Tân an châu đốc thuận Thơ hòa đốc lức Max Jan water Feb level Mar in Apr month May (m) Jun Mean Jan water Feb level Mar in Apr month May (m) Jun Mean Average

34 ANNEX 3. Salinity intrusion results for proposed scenarios 3.1 Salinity intrusion for SCN0 Table a23: Salinity concentration at some location in the Mekong Delta in SCN0 Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean Salinity intrusion for SCN1 Table a24: Salinity concentration at some location in the Mekong Delta in SCN1 Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean

35 3.3 Salinity intrusion for SCN Salinity intrusion for SCN2.1 with upstream flow as 2005 Table a25: Salinity concentration at some location in the Mekong Delta in SCN2.1-Q05 Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean Salinity intrusion for SCN2.2 with probability of 85% for upstream flow and upstream development Table a26: Salinity concentration at some location in the Mekong Delta in SCN2.2-Qp85% Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean

36 3.3.3 Salinity intrusion for SCN2.3 with near future dams with optimum operation Table a27: Salinity concentration at some location in the Mekong Delta in SCN2.3-NFD-opti Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean Salinity intrusion for SCN2.4 with the future dams and climate change condition Table a28: Salinity concentration at some location in the Mekong Delta in SCN2.4-RVCNA-opti Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean

37 3.5 Salinity intrusion for SCN3 Table a29: Salinity concentration at some location in the Mekong Delta in SCN3 Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean Salinity intrusion for SCN4 Table a30: Salinity concentration at some location in the Mekong Delta in SCN4 Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean

38 3.7 Salinity intrusion for SCN5 Table a31: Salinity concentration at some location in the Mekong Delta in SCN5 Max monthly Salt concentration (g/l) Mean monthly Salt concentration (g/l) Đại Cầu Trà Sơn Mỹ Hòa Tân Bến Gò ngãi quan vinh đốc hòa bình an lức Quao Jan Feb Mar Apr May Jun Jan Feb Mar Apr May Jun Max of month AVG of mean

39 ANNEX 4. Figure a3: Layout of sea dyke and proposed sluice for Water resource development plan in Mekong delta