Irrigation Systems and Water Stress Stimulation by Climate Change

During the stages of earliest human evolution in the past, people were motivated to build their settlements near rivers. The reason for this is “water”. Water is essential for life; hence irrigation systems are of paramount importance. However, the irrigation technology was not much developed at the time but, during the mediaeval world, irrigation industry was achieving a certain level of development. At present, irrigation systems are affected by climate change and face more serious consequences as the population depend on them. Climate change refers to long-term shifts in temperatures and weather patterns. This is a natural phenomenon which occurs due to the  variations in the solar cycle. However, since the 1800s, human activities and industrialization have been the main drivers of climate change.

Climate change leads to shifting weather patterns which leads to more frequent and intense drought, storms, heat waves, rising sea levels, melting glaciers and warming world, causing havoc on people’s livelihoods and communities. All these changes have affected the irrigation systems. Droughts are increasing in frequency and severity in many regions of the world due to climate change. The meteorological drivers of drought often because subsequent changes are the hydrology such as reduced catchment runoff, river flows and lake levels.

Hydrological Droughts

Hydrological droughts may also result in significant changes in water quality. Over the next 30–50 years most of the world’s major rivers are predicted to show large increase in frequency of hydrological drought conditions relative to the historic records over the last century (Hirabayashi et al., 2008). Increased water extraction for consumptive purposes also increases the likelihood of hydrological droughts occurring, regardless of changing climatic factors. More information can be reached here Archived

Flood Frequency

Additionally, many rivers are predicted to increase their flood frequency this century. In Sri Lanka’s dry zone, annual mean precipitation is about 1750 mm whereas annual mean evaporation ranges from 1700 mm to 1900 mm. About 80% of the annual rainfall occurs during the northeast monsoon season from November to February when flash floods often occur. Seasonal rivers and so-called Villu (wetland ecosystem in floodplains) are natural water bodies that emerge during these months.

The climate change has caused rainfall to behave erratically. Theoretically speaking what we experience today is a temporal variation accompanied with fluctuation in intensities. Climate change experts predict that Sri Lanka will experience longer dry spells frequently in the future. During such dry spells, often unforeseen, our reservoirs would be incapable of supplying the irrigation water demands continuously throughout the cultivation season.

Ancient Irrigation Systems

Sri Lanka has its own water irrigation systems adapted to climate challenges. Ancient irrigation systems such as Lakes, Wawa, Villu, Ellanga, diya kaduru are some of them. The International Union for Conservation of Nature in Sri Lanka identified four main functions of these ancient structures namely,  

• Capturing rainwater to minimize floods
• Storing rainwater
• Recycling used water
• Mitigating drought impact

Other than these, the cascade system sustained the local ecosystem as ancient engineers carefully used natural landscapes to enhance water storage. These techniques can be practiced to reduce water stress in an economically friendly manner. The following image shows the ancient Sri Lankan tank cascade system.  

Climate resilient Irrigation Systems

According to the IWMI, many water-scarce irrigation systems in the country, bear high climate risks. Adaptation to climate variability should happen on several fronts. Changes made by the irrigation management to the water release regime. Crop cycle, variety and Plant behavior should be considered to better manage the water. Changes in the cropping patterns practiced by farmers in the command area are good initiative for climate adaptation. More can be read here Archived

Use of groundwater, which is recharged from rainfall, is also worthy and such adaptation measures ensure that the available water supply over the two cropping seasons, even in drought periods. The Dry Zone, having recurrent droughts comprise of three-fourths of the land area spread over the Northern, North Central and Eastern provinces. Hence, such adaptations benefit agriculturally as well as in the economic front.

The other factor is flood risk from flash floods and heavy rains due to climate change. The flood mitigation of the tank cascade system entailed engineering techniques of water and sedimentation flow control along with the protection of banks from erosion. Ancient Sinhalese people constructed granite structures and pillars which protected the embankment from breaching and flooding, with improved technologies for metallurgy, iron was used to strengthen the structure. Another technique to controlled water level in flooding is using “Ellanga structures” which is a set of lakes connected with each other. This network is important because, the water level is controlled by transferring more water to reservoirs with less water.   

Global warming or the increase in atmospheric temperature is the root cause of climate change. Hence, the other major impact of climate change is an increase in evapotranspiration. Consequently, water requirement of the agricultural crops goes up demanding more water from reservoirs. In the meantime, water losses from the reservoirs themselves by way of evaporation will also increase. These scenarios will create more water stresses on irrigated agriculture in future.

Engineer, Thushara Dissanayake explains that, when the conditions are not favorable for agriculture there will be a sharp decrease in people engaged in agriculture abandoning their lands. Hence, this crisis should not be understood merely as a water crisis as it has the potential to have ramifications in other social and economic spheres. Therefore, the decrease in agricultural production will lead to higher selling prices, which neither the government nor the consumer is happy about.

Changes in climate will affect the water demand of crops grown in both irrigated and rain fed systems. An increase in temperatures will trigger a higher demand for water due to evapotranspiration by crops and natural vegetation, which will lead to more rapid depletion of soil moisture and more frequent crop failures. More can be read here Archived

Modern Sustainable Irrigation Techniques

1. Surface irrigation

Surface irrigation system is the most widely used option. With this type of irrigation, water is applied to the soil using gravity. Because the water distribution is not regulated, surface irrigation is also called flood irrigation. Furrow, basin and border irrigation are some methods under surface irrigation. More can read  here Archived

1. Micro-irrigation

Micro-irrigation system is a modern method of irrigation. This is efficient low-cost method for water management for agriculture purposes, since it delivers water slowly. Usually delivered in the form of discrete droplets, continuous drops, streams, etc.  

1. Drip irrigation

Drip irrigation is considered one of the most efficient and most modern type of irrigation technique used today. It helps reduce cases of runoff along with water evaporation. Control of weed growth, limited bacterial growth and water availability to plant roots are some advantages of drip irrigation.

To Sum up

Climate change leads to shifting weather patterns causing more frequent and intense drought, storms, heat waves, and more. This affects irrigation systems. Droughts cause subsequent hydrological effects such as reduced catchment runoff, river flows and lake levels and evapotranspiration. Flood risk also leads to soil erosion and crop damage. These effects pose a threat on social and economic status of a country. Sri Lanka’s traditional cascade and lake system had good initiative to mitigate climate change effects on irrigation. Modern irrigation systems are important because it has the ability to grow several crops or plants and enhance productivity, proper irrigation ensures healthy plants and modern irrigation helps to people against droughts or insufficient rainfall.