Thursday, Oct 7, 10:00-12:00 am CEST
SPIS Toolbox - Understand Water Resources
2. Understand Water Resources
The type of water source, the elevation or depth, the water quantity, resource responsibility, and quality all have a significant influence on establishing boundaries within which crop choices and decisions on the irrigation method can be made. The understanding of these aspects should be a first step in any SPIS planning or implementation project
Sources of water can be surface water, groundwater and non-conventional water. Typically, water for irrigation is extracted from rivers, lakes and aquifers. About 61 percent of the irrigated area worldwide uses surface water, and 38 percent groundwater. In Asia, Northern Africa and the Middle East, groundwater use has grown rapidly in recent years following the introduction of tubewell technology, accompanied by improved energy access and low energy prices (data from 2013, AQUASTAT 2016). Non-conventional sources, such as treated wastewater and desalinated water, provide a minor source of irrigation water globally (about 1 percent). The use of this water for irrigation is focussed in the Mediterranean, Middle East, and Andes regions.
The elevation difference between the water source and the field determines whether water can be delivered under pressure. This is particularly relevant for surface water for which it is important to understand whether gravity alone can support pressurised irrigation systems or whether it needs to be supported through pumps. For groundwater, the depth of the water table is decisive for the size of pump and the associated costs. Nowadays, pumps powered by solar energy can lift up water up to 200m (and increasing). However, these pumps are more expensive and less commonly available.
The available discharge from the source (the quantity of water) and variability is also important. Understanding what water resources are available, under what conditions, helps in deciding which irrigation method is most appropriate in the given environmental (climate, soils, and landscape) and agricultural context. When and how much does it rain during the year? What are the available surface and groundwater resources? What is the variability of these water resources throughout the year in terms of flow, quantity and quality? How variable is the water availability in the context of climate change? What are the requirements of other users? What are the environmental flow requirements?
The SAFEGUARD WATER – Water Resource Management Checklist tool helps to get a rough idea of the availability of water resources. In existing water scarce regions and regions predicted to experience water scarcity over the coming 20 years (see WRI predictions), it is advisable to run a more in-depth water balance analysis and feasibility study with tangible data before installing a SPIS.
A study should be conducted on the aquifer to establish sustainable abstraction rates. The responsibility of carrying out this analysis depends on the allocation of resource ownership within the watershed. In most cases it is prudent to establish a basin committee that engages the relevant stakeholders and takes responsibility for the aquifer analysis, as well as permitting, monitoring, and enforcement of abstraction. If resources are managed in a more fractured manner, then the permitting authorities should consider the impacts of their actions on the wider basin, other stakeholders, and the ecosystem. In either arrangement the resilience to future climate scenarios is key to the longevity of agricultural production.
The quality of water also needs to be taken into account as it affects the choice of irrigation method and the kinds of crops that can be grown. Both the chemical composition of water and the sediment load can influence this choice. The presence of certain elements, like sodium (Na), chlorine (Cl) and Boron (B), beyond a certain threshold, can cause leaf burn and defoliation under sprinkler irrigation. Similarly, the total concentration of salts in water affects leaching requirements, which makes saline water not very suitable for furrow irrigation. The sediment load of water determines the filtration requirement for drip irrigation and the selection and maintenance program of drippers, hence, its applicability under certain conditions. Similarly, sediments increase the wear of pumps and other components of sprinkler
- Identification of key factors determining irrigation method
- General overview of how water quantity, quality and variability
- Awareness of environmental hazards that need of specific attention
- Establishment of basin committee or structured means of assessing sustainable abstraction
- Understanding the need for governance of water resources
- Awareness of the risks posed by climate change and the need to be resilient
- Information on the source of water (surface, groundwater, non-conventional water) and its behaviour (recharge rates, drawdown rates, etc.)
- Information on the elevation between water source and field
- Information on water availability, quality and flows.
- Information on future water availability scenarios
- Information on other user requirements upstream and downstream
- Water Resources Management and Licensing Authority
- Hydrological services
- Irrigation managers, water user groups or farmer organization
- Downstream water users
- Environmental protection agencies or similar, environmental NGOs
- No irrigation development can take place without a legal water abstraction permit or similar.
- Water abstraction quotas are binding and constitute the maximum water availability for peak demand.
- Assess climate risks and understand the limitations that exist for water supply system.
- Regular review of the permits is necessary to ensure resilience and fair allocation of water resources as the climate and water availability change.
- Aquifer and watershed analysis are necessary to understand the hydrological system, foresee impacts of the SPIS, and mitigate negative outcomes.