Hello. My name is Matt Hipsey. And I'm an environmental scientist who works in the area of water. The study of water science is called "hydrology." Whether we live in an arid environment or a tropical zone or anywhere in between, then careful management of water resources is critical for sustainable farming. Water is an essential ingredient for both animal and crop production, but very often we are faced with the challenge of too much water or not enough. Climate change also has the potential to significantly alter the water resources available to farmers, and developing a plan for sustainable farming must give due attention to how our water resources might change in the future. When we think of water, we immediately think of rivers and dams. But did you know that every piece of food you eat also has a water footprint? The amount of water used depends on the type of food being produced and can range from 1,300 liters for a kilogram of wheat through to greater than 4000 liters of water to produce one steak. At a global scale, one of the biggest uses of water is irrigated agriculture. And it is estimated that the total water consumed to produce food is 10 times higher than what is required for personal or municipal water use. The high consumption of water by irrigation quite often leads to water shortages. If water demand by farmers exceeds supply, then allocations to farmers can be reduced. And this impacts on their livelihoods and inevitably leads to the over exploitation of water supplies. This is a complex policy problem in many countries around the world. In contrast to irrigated agriculture, rain fed agriculture relies on growing crops using what is delivered naturally from the sky. In these systems, the total crop yield is highly correlated with the amount of rainfall received in any given year. And these farms are therefore very sensitive to changes in climate. In rain fed systems, the most important indicator of water availability is the soil moisture content, how much water is available in the soils that can be taken up by roots. Although irrigated and rain fed agriculture are very different, they are both highly sensitive to water shortage. The disciplines of water resource management and water resource engineering have been created to find solutions to water related issues. Whilst the solutions always needs to be very site-specific. At the heart of any hydrological study is the concept of a water balance. The water balance is a means by which we can account for the stores and the flows of water. Only once we have a good understanding of the water cycle for a given region can we successfully manage our most precious resource. Undertaking a water balance requires us to first define the area of interest. This is usually a catchment or it could also be done at the scale of an individual farm or farming district. The water balance states that the change in storage of water occurs at a rate depending on the inflows and outflows. Typical storage as we consider includes surface water stores such as dams, storage in groundwater aquifers and also storage in the upper soil, which we call the "vadose zone." Depending on the store, we then account for flows of water due to the different hydrological processes. An example that can be done is the soil water balance that we may do in the context of assessing crop water use. This demonstrates that the water stored in the soil, which is related to soil moisture, depends on the rate of evaporation and transpiration to the atmosphere. The amount of percolation to deeper layers within the soil profile, and also runoff from the surface. Runoff occurs when the soil infiltration capacity is lower than rainfall intensity or when the soil is already saturated with water. So, let's now do an example calculation of a soil water balance for a hypothetical hill slope. First, read the problem and then draw a diagram that summarizes the information as best you can. Then when you've done that, write out the water balance equation specific to this problem. Finally, we rearrange to solve for the unknown quantity, which in this case is the amount of runoff. If we are looking at irrigating our crop with ground water, we can also undertake a water balance on the regional groundwater system, what we call an "aquifer." In this case, we compute groundwater flow based on differences in water table heights underground, and we must also consider the rate of vertical recharge from rainfall, and consider that in a lot of the amount of extraction from wells. If the rate of extraction exceeds the recharge amount, then water levels can drop unsustainably, and monitoring groundwater levels is, therefore, critical to understand if the amount of water extraction is sustainable in the long-term. Conversely, in dry lands where cereal crops grown, the clearing of trees can lead to a reduction in the overall rate of transpiration and a rise in the ground water level. If that ground water has a high level of salts and land salinization can occur, and there's a serious land management issue. Managing surface water is also a critical challenge. Storing water in dams is necessary to supply crops and stock over the dry season. But how big should that storage be? We can again use the water balance concept to aid us plan and design surface water storages. Loss to evaporation, in particular, can be large in warm climates and needs to be factored in carefully when computing how long water will last for. As an example, let's do another calculation, this time to estimate how long water in a dam will last. As before, first, read the problem and sketch a diagram summarizing the information provided. Then we write out the water balance equation specific to this problem defining what is the change in store we're considering and the inputs and outputs. [MUSIC] In areas where the amount of rainfall is much less than the annual rate of potential evaporation, then we can augment dam water supplies by enhancing them amount of water harvesting. A common approach we use in Australia is the use of roaded catchments that are highly efficient at generating runoff from relatively low rainfall amounts. Within our Future Farm 2050 Project we have paid careful attention to ensure the design of our dam and roaded catchment will ensure sufficient water for stock both now and into the future, and considering projections of increased drought severity due to climate change. Without careful management of water then we can create serious environmental impacts. We have to think not only of the water we need, but also how our actions may impact ecosystems downstream. There are three main ways that farm scale water management actions can adversely impact the environment. Firstly, the removal of water from natural watercourses into reservoirs and storages reduces the amount of water flowing downstream. And this can threaten the supply of water to ecosystems that depend on it. Secondly, water that is leaving the farm is often impacted by fertilizers and pesticides, which accumulate in the runoff and impact water quality when the water returns to the downstream water course. Thirdly, changes to the water table height can change the natural regime of surface ground water interaction. For example, when extractions are high, lowering water tables may lead to reduced water for nearby groundwater dependent ecosystems such as wetlands. Conversely, in the case of dry land systems, increases in the water table may result in increased loads of salinity entering rivers through increased seepage. This has been the case at UWA Farm Ridgefield. And restoration efforts are being undertaken using strategic revegetation to lower the ground water level and improve stream salinity. The key to sustainable water management on any farm is to look holistically at water storages and understand the key hydrological processes. Because the water balance manifests differently in different environments, each case study needs to be considered individually. Fortunately, there are many great resources available online that can aid in your study of water management and help you identify the key issues and best management approaches for any particular situation. I've provided some additional readings to aid in your study of water management. [MUSIC]
