The Relationship Between Hydrology and Global Climate Change
Clouds building through evaporation on a hot, humid afternoon
Rapid storm runoff reduces water availability for future evapotranspiration, resulting in drought.
HYPOTHESIS ON THE EFFECTS OF EVAPORATION AND TRANSPIRATION ON THE CHANGING CLIMATE
By Trevor Wicks
Droughts, Wildfires and Record High Temperatures - Is Our Climate Going Down the Drain?
Background:
The global climate is changing. This hypothesis examines the effect of human change on the earth's water cycles (hydrology) to help understand one of the causes of global climate change.
The climate on the Central East coast of Vancouver Island is changing at an alarming rate. The period of reduced rainfall, warmer temperatures, lower humidity and higher ground wind speed has extended by several weeks. The dry season is starting earlier in the spring and lasting later into the fall. Within a short period of time the temperate rain forest climate is being transformed into a Mediterranean or California climate. This region's climate change is largely the result of human impact on the area's hydrology.
The challenge is to create a better understanding of the cause and effect of this hydrologic climate change, and to develop effective actions to help slow down these trends.
Climatic Cycles:
- Microclimate:
- The cool breeze from a small lake on a hot day.
- Regional climate:
- The rain-shadow effect from a mountain range combined with the cooling of the air from a large forested area.
- Continental cycles:
- The compound effects of the above with oceanic and polar influences.
- Global climate trends:
- The compounded effects from above with the impacts of greenhouse gasses or changing ocean currents etc.
The climate in a specific location can be influenced by different climatic cycles during the year. For example the winter climate on Central East Coast of Vancouver Island is dominated by the effects from the ocean and the continental land mass. The spring, summer and fall climate is primarily influenced by the rain-shadow effect from the mountains, and evapotranspiration from the land surface in the region.
Regional Climate and the Hydrologic Cycle:
A large proportion of spring, summer and fall precipitation originates from evapotranspiration that occurs within close proximity of the rainfall. In a balanced environment a significant percentage of that rainfall would then be recycled through the evaporation and transpiration into the atmosphere, then condensing to fall as rain again within the same region.
Precipitation will only occur when sufficient moisture is evaporated or transpired into the atmosphere. If water or moisture is not available for evapotranspiration, the amount of precipitation and the formation of overnight dew will be reduced or eliminated. When the hydrologic cycle is interrupted there becomes less and less water / moisture to recycle within the region.
The Effects of Evapotranspiration in Two Climatic Extremes:
High water/moisture climatic cycle:
Tropical Rain
Heavy clouds
High Air turbulence
High humidity
Lower wind speed
Cooler moderate temperatures
Little ground level radiant heat
High evapotranspiration
High levels of available water/moisture
Low water/moisture climatic cycle:
Forest Dry Desert
No clouds
Little air turbulence
Low humidity
Higher wind speed
Extreme temperatures
High ground level radiant heat
No evapotranspiration
Minimal available water/moisture
Evapotranspiration is a Powerful Force:
Another part to the climatic jigsaw puzzle is water's capacity to transfer heat energy. It takes six hundred thousand calories of heat energy to evaporate one liter of water. The land surface can evaporate more than 10,000,000 liters of water per hectare in one year, and a single mature tree can transpire or evaporate 150,000 liters of water annually. When moisture is unavailable to be evaporated or transpired, this heat transfer process stops; the thermal energy is not absorbed and retained as latent heat in the humid atmosphere.
Higher temperatures, low relative humidity, and high wind speed, increases evapotranspiration, from bodies of water and land with high levels of available water / moisture. This results in extreme weather events and storms, because the heat energy and moist air is concentrated into a large powerful force.
Human Influence Over Water / Moisture and the Climate:
Many of the practices that are taken for granted; draining water off the land, extracting vast quantities of ground water from aquifers, creating large impervious surfaces, eliminating wetlands and reducing the amount of forest land are affecting regional and global climates. These land use activities disrupt and even eliminate evapotranspiration from the earth's surface; this in turn alters the thermal balance in the atmosphere, and the hydro-climatic recycling of water.
Recent worldwide trends show a lowering ground-water tables, reduced surface water area in lakes, wetlands and soil moisture, and the reduction of forested land. This in turn affects climatic cycles, including the potential for rapid global warming.
The Easter Island Example:
The 166 sq km. island in the South Pacific is an example of how human impact on the land affects the “hydro-climatic cycle”. Overpopulation and land modification eliminated most of the vegetation and available soil moisture on the island, destabilizing the hydro-climatic balance. Easter Island is now dry and barren; a thousand years ago it was a lush humid tropical island covered by a blanket of cloud, the island probably experienced heavy rainstorms on most days.
The Critical Point:
The loss of water/moisture in the soil, plants and trees can reach a critical level; precipitation from that imbalance can be less than the amount required for human, environmental and agricultural needs. At that point there becomes less and less water/moisture available to restart the hydro-climatic recycling process. The compounding effect causes drought and in turn increasing temperatures, reduced groundwater levels, lower river and lake levels, die-off of trees and vegetation, increased wildfires, and extreme weather events.
Preserving a Stable Climatic Balance:
In order to maintain a more sustainable hydro-climatic balance we need a program of:
- Improved data collection and evaluation of changes to groundwater aquifers, surface water runoff, and available evapotranspiration moisture levels
- Public awareness and education for government officials, planners, engineers, developers, forestry and agricultural professionals
- Development of regional action plans to introduce best management practices and strategies to maintain the balance between land use impact and hydro-climatic changes which include the following:
- Improved storm-water utilization techniques and reducing instant run-off
- Creating more water infiltration capacity to raise groundwater levels
- Balancing water usage with the recharge or recovery rate
- Encourage water conservation
- Re-vegetation, planting trees
Thank you for taking the time to read this hypothesis,
