Introduction to water resources assessment (WRA)

Definition of water resources assessment

According to the World Meteorological Organisation (WMO), its definition is 

'the determination of the sources, extent, dependability and quality of water resources for their utilization and control, and water resources are the water available, or capable of being made available, for use in sufficient quantity and quality at a location and over a period of time appropriate for an identifiable demand.'

General approach

To assess, according to the oxford dictionary, means to evaluate or estimate the nature, ability, or quality of something. For one to complete water resources assessments, the various ways in which the water resources are affected (through changes in inflow/outflow/storage and their interrelationship) and its nature (i.e. variability) must be studied and understood. The figure below shows how a hydrological system is normally conceptualised.

Figure1. A simple conceptualisation of hydrological system.

A comprehensive WRA will allow the hydrologists to estimate the volume of sustainable surplus flow, which could then inform the decision makers on related development and water management e.g. the construction of dams, although this is not always the case. It is particularly important nowadays given the uncertainty and risks surrounding the issue of climate change and biodiversity loss as well as the impact of population growth and rapid urbanisation in Africa, all of which wield significant influence on the hydrological system itself (). In line with the 2015 sustainable development goals, the WRA should guide water resource management (WRM) in ways that will allow both the present and future population enjoy clean and adequate water supplies to meet their social, economic and environmental needs. 


Scales of water resources assessment

All water resources assessments need to have a clear hydrological boundary. Without it, data collection cannot be done. ideally, one should consider all the following factors in drawing up the boundary 

• River watersheds
• Groundwater systems
• Administrative divisions
• Transnational boundaries

and the characteristics of the surface water and groundwater flows.

What are the steps then?

See Fig2 for a work-flow diagram.

1. Define boundaries of assessment
2. High level review to determine dominant behavior and processes
• Which processes are significant in this catchment e.g. In Taiwan, due to its steep relief of river channels, surface flow is vital in model representation.
3. Data collection
• Hydrometerological and hydrogeological: climate (rainfall, temperature, moisture level), surface water flow, groundwater level 
• Biophysical: topography, vegetation, geology and soil
• Socio-economic: land use, demography, 
• Water use: water consumption by adminstrative region
4. Data analysis
• It needs to address the inherent natural variability of the hydrological system. e.g. In southern Africa, its riverflows are characterised with very high variability (σ/μ) that respond dramatically to reduction in precipitation (10% less rain --> 17-50% less discharge). This is essential to understand water availability and thus to WRM. 
• Water quality should be incorporated as contamination of water reduces water availability and its consumption could lead to many health and economic issues. e.g. Globally, around 2000 children are killed by diarrhea every day, much more than AIDS, malaria, and meases combined.
• The environmental flow, a concept that is increasingly being adopted in WRA, is the minimum volume of flow that is needed to maintain the environmental integraty and biodiversity of the hydrological system and the human society that it supports.
5. Modelling the changes in catchment behaviour
• e.g. Thompson et al (2013)'s modelling results showed that the risk of ecological impact from changes in discharge increases in River Mekong, especially for low-flow seasons. 
6. Assess sustainable and exploitable water over evaluation period
• e.g. Thompson et al (1995) through incorporating various different operating scenarios of dams demonstrated that further construction of dam could lead dramatic reduction in water downstream, affecting the income and livelihood of those relying on agricultural productivity. 
7. Presentation of water resources assessment

Figure2. Workflow of WRA.

Hope you enjoyed reading this post, next week I will be blogging about the history of WRA in South Africa.