Climate change and the future of Okanagan water resources
Posted December 2005
Climate change is a topic occupying many people’s minds. Statisticians examine decades of climate data looking for trends; scientists pursue the development of temperature and precipitation models to predict future climatic fluctuations; politicians argue about reducing greenhouse gas emissions; and the world’s citizens look to an uncertain future for their children and grandchildren. Many studies have determined that global climate patterns are changing. But what does the future hold for us here in B.C.? A group of researchers set out to answer that question.
Released in 2004, Expanding the Dialogue on Climate Change and Water Management in the Okanagan Basin, British Columbia is the final report resulting from a multi-year, collaborative effort of researchers from Environment Canada, Agriculture and Agri-Food Canada, UBC, the BC Ministry of Water, Land and Air Protection, and the District of Summerland. As the report’s title implies, their focus centred on the Okanagan Valley.
The valley is 182 km long and runs from Armstrong to the B.C./Washington border. The area comprises a range of climatic zones from arid to moist, however, the valley bottom can best be described as semi-arid. Extensive irrigation supports a large and economically important agricultural sector. Water resources are further being strained by the region’s continually growing population. Temperature and precipitation variations caused by climate change would therefore, have a profound effect on the valley’s water resources.
The Okanagan’s Changing Climate
Observations show the valley’s climate is changing. It appears there is a definite shift to a warmer and wetter climate, making it more rainfall-dominated. Some monitoring stations have registered significant winter and spring temperature increases. Daily maximum temperatures have increased, however, daily minimum temperatures are rising more rapidly. During the last century, the number of frost-free days has increased by about 3.1 days per decade. Regional scenarios developed using different Global Climate Models show that winter and summer mean temperatures will increase by two to four degrees Celsius in the coming decades.
Precipitation patterns are also changing. Previous decades have seen an increase in spring and summer rainfall. Monitoring stations at lower elevations have shown a lower percentage of precipitation falling as snow, and the snow water equivalent was reduced in previous decades. Snowmelt also seems to be occurring earlier than previously observed. Scenarios suggest that mean winter precipitation will increase by five to 25 percent. Summer mean amounts are projected to decrease by five to 20 percent or perhaps even more.
Effects on Water Resources
There is inherent difficulty in projecting changes to regional hydrological processes based on global climate change predictions. Every area possesses its own unique set of characteristics that determine its hydrological regime. The Okanagan is no exception. In fact, the region contains a wide variety of microclimates. For this reason, the regional climate models that were developed show different projections. They can however, be useful in planning for future changes to the region’s water resources.
Studies have determined that the Okanagan’s water resources may be particularly susceptible to climate change-induced effects due to the region’s arid and/or semi-arid climate. Evapotranspiration processes form a significant part of the area’s hydrology. Temperature increases can greatly affect runoff in systems such as this. Even small variations in precipitation can cause significant changes.
Projections point to an earlier spring snowmelt of up to eight weeks. Reduced snowpack volumes and increased winter and spring temperature-induced evapotranspiration rates will significantly decrease peak flow volumes in later decades. The number and size of flood occurrences is expected to decrease. As was previously mentioned, the valley’s climate is predicted to become more rainfall dominated. Annual flow volumes are also expected to decrease considerably. As a result, Okanagan Lake inflow will be significantly lower.
The projected higher winter temperatures will increase the number of rain events, which will decrease the size of the snowpack. Additionally, snowmelt will occur more quickly with a higher number of rain-on-snow events. This will lower water flows in the summer when water demand is at its peak. The accumulation of the snowpack is expected to begin later in the season, with the peak occurring earlier. This coupled with the earlier occurrence of snowmelt means the snowpack will be present for a shorter time.
Managing For an Uncertain Future
There are many factors to consider in the management of the Okanagan’s lakes and reservoirs. Managers must consider all water users. Water must be made available for agricultural irrigation, domestic uses, and industrial operations. However, operators must also ensure adequate environmental flows to support and maintain aquatic ecosystems, and provide flood-control measures. If flow volume and timing are altered due to climate changes, the task of managing the region’s water resources will become more difficult.
With reduced snowpack volumes, earlier and more rapid snowmelt, and reduced non-peak flows, managers would see most of the yearly flow enter the reservoirs during a short time period. They would not only have to contend with these higher volumes, but would also have to retain enough water in the reservoirs to provide for the increased demands that occur during the hot, dry growing season – a season that could become longer and hotter due to climate change effects. This is already a time of reduced flows, however, they would be further reduced due to climate changes. Water supply disruptions could potentially occur. With a smaller snowpack, managers would also be less able to use snow volumes as a means of predicting flow conditions, thereby making reservoir management more difficult.
The importance of maintaining adequate environmental flows to sustain aquatic ecosystems particularly during fish spawning times is well understood. However, what would happen if the needs of all water users could not be met during times of low water flows? Which sector would be deprived of the needed water? Would a lower priority be placed on environmental needs? These are questions managers may have to answer with increasing regularity if climate change projections are accurate.
Basically, climate change scenarios predict significant changes to the valley’s water resources. These changes do not appear to be positive. Indications of reduced flow volumes show that the future availability of the region’s water resources is indeed uncertain. Added to this uncertainty is the knowledge that water demands will continually increase. Hotter, dryer, and longer growing seasons coupled with reduced flows will make it increasingly more difficult to satisfy the needs of all water users, as well as environmental needs.
Water shortages could become an increasingly regular occurrence. Water supplies could possibly be increased through the development of more reservoirs, increasing the existing storage capacity, and/or modifying current management procedures. However, wide-scale water conservation measures must be implemented for all water users. This study paints a bleak picture of the future of the Okanagan’s water resources. It is in all our best interests to take notice and look for ways to alter our water-thirsty behaviours and prevent climate change. Our very future depends on it.
For more information go to: Expanding the Dialogue on Climate Change and Water Management in the Okanagan Basin, British Columbia.