Freshman Geography Lecture 5

Course Overview

  • Title: Geography of Ethiopia and the Horn
  • Author: Belete Ejigu (PhD)
  • Affiliation: Assistant Professor of Urban Planning and Development, Addis Ababa University
  • Course Type: Freshman Course
  • Date: January 2021

Chapter Five: The Climate of Ethiopia and the Horn

Objectives

  • Understand and distinguish between weather and climate.
  • Identify spatiotemporal patterns of temperature and rainfall in Ethiopia.
  • Analyze climate implications on biophysical and socioeconomic aspects.
  • Comprehend the mechanisms of climate change impacts and responses.

Introduction

  • Ethiopia's climate is influenced by:
    • Variety in altitude and topography.
    • Proximity to the equator and the Indian Ocean leads to pronounced weather and climate variations.
      -Main controllers of climate include:
    • Seasonal migration of the Inter Tropical Convergence Zone (ITCZ)
    • Atmospheric circulations

Weather vs Climate

  • Weather: Short-term atmospheric conditions.
  • Climate: Long-term average of weather conditions (decades).
  • Climate is established through composite of daily weather records over a long time.

Elements and Controls of Weather and Climate

  • Major Forces influencing weather:
    • Wind: large scale horizontal air movement.
  • Climate determined by:
    • Radiation (amount and distribution)
    • Latitude, altitude, nearby water, ocean currents.

Key Elements of Climate

  1. Temperature
  2. Precipitation
  3. Humidity
  4. Winds and air pressure
  5. Ocean currents

Controls of Weather and Climate

  • Latitude: Distance from the equator affects solar exposure and temperature.
  • Inclination of Earth's Axis: Influences seasons and daylight length.
  • Altitude: Higher elevations usually mean cooler temperatures.

Detailed Examination of Climatic Controls

A. Latitude

  • Influences temperature patterns:
    • Colder as you move from equator to poles.
    • Ethiopia's location results in:
    • High average temperatures.
    • Small temperature variations seasonally.

B. Inclination of the Earth's Axis

  • Affects directness of sun's rays and seasonal changes.

C. Equinoxes and Solstices

  • Equinoxes: Equal day and night lengths.
    • Vernal Equinox: March 21
    • Autumn Equinox: September 23
  • Solstices: Unequal day lengths.
    • Summer Solstice: June 21 (longest day in the North)
    • Winter Solstice: December 22 (shortest day in the North)

D. Altitude

  • General Temperature Decline with increased elevation.
  • Lapse Rate: Average 6.5°C decrease per kilometer.

Types of Lapse Rate

  1. Dry Adiabatic Lapse Rate: Temperature change due to expansion/compression without heat exchange.
    • Approximately 10°C per 1,000 meters.
  2. Wet Adiabatic Lapse Rate: Occurs when air condensation releases latent heat.
    • Average cooling is around 5°C per 1,000 meters.
  3. Environmental Lapse Rate: Actual temperature changes with altitude, around 6.5°C per 1,000 meters.

Spatiotemporal Patterns of Temperature and Rainfall in Ethiopia

Temperature Distribution

  • Altitude and latitude determine temperature distribution significantly.
  • Mean annual temperatures range from >30°C in lowlands to <10°C in highlands.
  • Variations due to cloud cover and geographical features.

Rainfall Distribution

  • Complex rainfall systems influenced by the ITCZ, pressure cells, and trade winds.
  • Temporal variability with major rainy seasons occurring in summer and minor seasons in spring/autumn.

Rainfall Regions of Ethiopia

  1. Summer Rainfall Region: Predominately July and August, except southeast and northeast lowlands.
  2. All Year-Round Rainfall Region: Mostly southwestern Ethiopia, heavily influenced by equatorial westerlies.
  3. Autumn and Spring Rainfall Regions: Southeast lowlands experience rain during equinoxes.
  4. Winter Rainfall Region: Northeasterly winds bring moisture to specific areas like Afar during winter months.

Agro-ecological Zones of Ethiopia

  • Defined by altitude and climatic conditions, these include:
    • Bereha: Hot arid (below 500m)
    • Kolla: Warm semiarid (500-1500m)
    • Weyna Dega: Cool sub-humid (1500-2300m)
    • Dega: Cool to humid (2300-3200m)
    • Wurch: Cold, altitudes >3200m.

Climate Change Overview

  • Defined as long-term changes in climate due to natural variability or human activity.

Causes of Climate Change

  1. Natural Causes: Variations in energy budget, Earth’s orbit, volcanic eruptions, etc.
  2. Human-induced Causes: Greenhouse gas emissions from various anthropogenic activities.

Consequences of Climate Change

  1. Health Impacts: Increased morbidity/mortality from heat, disease spread.
  2. Water Resources: Altered availability, leading to droughts and floods.
  3. Agriculture: Change in yields and crop viability.
  4. Ecosystems: Risk of extinction for vulnerable species.

Response Mechanisms to Climate Change

  1. Mitigation: Efforts to reduce greenhouse gas emissions.
    • Strategies include renewable energy use and energy efficiency.
  2. Adaptation: Adjustment strategies to cope with climate changes.
  3. Resilience: Building the ability to withstand and recover from climate-related difficulties.

Discussion Questions

  1. Differentiate between weather and climate.
  2. Which climatic control predominantly affects Ethiopia's climate and how?
  3. Describe the spatiotemporal distribution of temperature and rainfall in Ethiopia.
  4. Discuss temperature dynamics in Ethiopia—is it warming or cooling?
  5. Identify causes of climate change.
  6. Discuss responses to changing climate.