Projecting water demand and availability under climate change through the application of WEAP in the Nam Ngum downstream area, Laos

Author: Phingsaliao Sithiengtham

Sithiengtham, Phingsaliao, 2019 Projecting water demand and availability under climate change through the application of WEAP in the Nam Ngum downstream area, Laos, Flinders University, College of Science and Engineering

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Water is one of the most vital resources. Rapidly increasing water demand threatens water resource availability in many regions across the world. Equitable and sustainable water allocation planning is considered important in the context of anthropogenic threats, such as climate change and over extraction. To allocate water efficiently, it is essential to understand the water balance of an area.

The Nam Ngum River Basin (NNRB), Laos was selected as a case study. This research aimed to determine how much water is currently needed and available as well as to project future water demand and availability according to population growth, industrial development, agricultural intensification, and climate change until 2050. The study employed the ‘Water Evaluation and Planning (WEAP)’ model as a key tool to simulate the water balance of the area.

The results reveal that water availability is much more than the current water demand in the Nam Ngum downstream area. The current annual water extraction is around 372.5 million m3, with primary users being the agricultural (95.7%), domestic (3.8%), and industrial (0.5%) sectors. The water inflow to the area is around 20.66 billion m3/y, which is coming from the Nam Ngum 1 dam and Nam Lik River inflow (83.6%), rainfall (15.7%), and the Nam Mung 3 dam (0.8%). The Nam Ngum River is also gaining water from groundwater. The river runoff from the area is approximately 19.7 billion m3/y, which is 53 times higher than the demand. In this case, the amount of water extracted can increase up to 46 times without major environmental flow impacts, whereas 96 m3/s is preserved for the minimum flow requirement.

In the future, water demand will continue to increase, while water availability will vary according to climate conditions. By 2050, the estimated annual water demand will be approximately 3.3 billion m3, which will be an increase of 8.9 times relative to the current usage. In a very wet year, the Nam Ngum River runoff from the area is projected to be 48 billion m3, which is 129 times higher than the current demand. In a wet year, the water availability is estimated to around 90 times higher than the current demand. The minimum river flow is projected to be 250 m3/s in very dry years. Total river runoff in a very dry year is around 11.4 billion m3/y equivalent to 30 times the current usage. Thus, in the dry season of an extremely dry year, water might still be adequate to meet the increased demand. However, if the inflow has been halved, the minimum flow requirement of 96 m3/s might not be met in the year of 2050 if that year experiences a severe drought.

Although sufficient water is currently available, it needs to be managed and allocated properly. The water in the system does not distribute equally to all zones in the Nam Ngum downstream area. Furthermore, anticipated increases in levels of extraction together with projected impacts from climate change are likely to result in greater demand on water availability. Thus, it is imperative to establish water allocation and sustainable river basin management plans to allocate water for all users equitably and to manage water resources for sustainable use. In addition, further related research should include examination of water quality and the required flow dynamics of the river discharge as important aspects of environmental flows and water availability.

Keywords: WEAP, water balance, water demand, water availability, climate change

Subject: Water Resources Management thesis

Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: Strategic Professor Okke Batelaan