How do the cycles and modes of the Pacific Ocean affect the water cycle?

The water cycle describes the continuous transfer of water between the land, the atmosphere and the oceans.  It has many physical components that can be divided into two general categories: reservoirs and pathways.  Reservoirs are places where moisture is stored, such as glaciers, ice caps and sheets, permafrost, groundwater, lakes, rivers, wetlands, oceans and the atmosphere.  Pathways are the mechanisms by which the moisture is transferred between these reservoirs.  They include precipitation, transpiration, evaporation, surface flows, and subsurface flows.  All of these components are strongly interconnected, such that when one is affected (e.g. by climate changes), the others are often affected as well.  Such changes can have substantial impacts on ecosystems, weather patterns, water quality and availability as well as power generation.

One important factor which is capable of influencing the water cycle on the Pacific coast, as well as across North America, is the Pacific Decadal Oscillation (PDO).  This is a pattern of climate variation which is characterized by 50-70 year cycles involving a positive and a negative phase, each of which lasts 20-30 years.  The positive phase is described as warm-dry weather, which is similar to, but not as pronounced as the effects of El Niño.   The negative phase is described as cool-wet weather conditions, similar to La Niña effects.  It is proposed that the unusual and somewhat extreme weather events on the West Coast may be a result of a recent transition into the negative phase of the PDO. 

Goals:

The aim is to provide policy makers with reliable scientific information predicting long-term variations in the Canadian climate such that policy decisions can be made that support appropriate climate change adaptations.

Methods:

Scientists are able to identify historical climate variations by analyzing the composition of cores of annually laminated marine sediments from anoxic coastal inlets of British Columbia, including Effingham Inlet.  These sediments appear in the form of light and dark layers.  The light diatomaceous layers are a result of algal blooms during the warm summer months, and the dark terrigenous layers are related to the amount of precipitation, particularly in the winter months.  Therefore, the pattern of these layers in a sediment core indicates what the weather conditions were like in past years.  Also, they can indicate previous climate change events possibly related to the PDO, and therefore allow scientists to predict when such changes may occur again, and how long the effects may last.

Results:

Historical analysis appears to reveal that the last climate “regime” shift occurred around 1976-1977.  From the mid-1940’s to the mid-1970’s, the climate on the West Coast was cooler and wetter, and from 1977 to 1997, the West Coast has enjoyed relatively warmer, drier weather.  However, scientists are now hypothesizing that there has been another regime change around 1999 towards a period of cooler, variable weather.  It is thought that the strong El Niño event of 1997-1998 followed by the moderate La Niña event of 1998-1999 may have catalyzed this regime shift (Dallimore et al., 2005).  If in fact such a regime shift has occurred, the West Coast will have to adapt and plan for cooler, stormier, more unstable weather for the next 20-30 years.

The relative positions and intensities of the north Pacific “weather-makers”, the Aleutian Low in winter and the North Pacific High in summer, affect the position of the Jet Stream across North America as well as the amount and timing of precipitation all the way from the Pacific coast to central Canada.  Looking back in geologic time using laminated ocean sediments gives us an idea of the range of changes in these atmospheric systems and how these changes, in turn, affect ocean processes and ecosystems.  With this knowledge, we can understand the changing climate we are now experiencing and look forward to predict the range of changes we may reasonably expect in the future (Hay et al., 2007).   

Potential Impacts of Pacific ocean cycles (Climate Change) on some of the Components of the Water Cycle:

1) Precipitation:

• Increases in the frequency and intensity of rainstorms are expected, as well as sea surges and wind storms that could cause damages such as the sedimentation of Vancouver drinking water reservoirs during intense rainstorms of November, 2006 which resulted in the largest boil water advisory ever issued in Canada (2 million Vancouver area residents were without potable drinking water for ten days).
  
• Storm events could affect infrastructure for storm water management.
  
• Changes in timing and amount of precipitation can also lead to drought and water shortages as was experienced in the B.C. coastal community of Tofino in the summer of 2006.
  
• Potential future decreases in precipitation could impact water management and storage planning.

2) Groundwater:

• Decreased quality due to increased mineral solubility and decreased dilution of contaminants in surface water bodies (turbidity).

3) Lakes and Reservoirs:

• Hydroelectric power generation challenges due to changes in the timing, intensity and magnitude of spring runoff.

4) Streams and runoff:

• Larger and/or more frequent severe floods causing increased expenditures.
  
• Increased erosion of banks.
  
• Decreased water quality due to increased contaminant concentrations (turbidity).

NASA – The Water Cycle

Variations in the Pacific Decadal Oscillation over the past millennium

An historical narrative on the Pacific Decadal Oscillation, inter-decadal climate variability and ecosystem impacts