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For more information about this project, please contact the authors, Kelly Hopping and Greg Wann.

Introduction

Ethiopia is faced with a crisis of great magnitude. A time of crisis is also a time of opportunity, for changes do not occur in times of stability and prosperity. We must use this opportunity, or else we will perish, as many civilizations have done before.”

(Tewolde B. G. Egziabher, 1988)

Climate Change

Although Egziabher was referring to a crisis of environmental degradation in the 1980s, his statement may equally apply to unprecedented changes that will occur as a result of changing climate and its consequent effects. Global environmental change is occurring at unprecedented rates and will likely have disproportionate impacts on marginalized groups who depend heavily on their natural resource base (Boko et al. 2007). Spatially explicit, predictive models can serve as important tools to help reduce the vulnerability of social-ecological systems to changing climate (O’Brien et al. 2004). Possible future scenarios produced by these models may be used to inform decision-making at multiple scales with the aim of mitigating unforeseen, undesirable responses to global change (Millennium Ecosystem Assessment 2005).

Under projected global climate change scenarios, Ethiopia is predicted to experience shifts in both temperature and precipitation. Changing climate variables will affect ecosystem functioning via, for example, altered evapotranspiration, runoff and hydrology (Christensen et al. 2007). The 4th report of the Intergovernmental Panel on Climate Change (IPCC) reports that minimum temperatures are predicted to increase slightly faster than maximum or mean temperatures (Christensen et al. 2007). In some areas these temperature changes may be beneficial to human population growth. For example, higher temperatures and rainfall in the highlands would create lengthened agricultural growing seasons capable of producing greater crop yields (Thornton et al. 2006). However, temperature increases are also predicted to allow the spread of temperature-dependent disease vectors and hosts into previously uninfected areas (Tanser et al. 2003).

As human populations throughout the world and in Africa, specifically, simultaneously grow and attempt to cope with climate change, it is anticipated that conflicts will arise in response to novel or intensified structural inequalities, resource mismanagement, and other unforeseen stresses (Boko et al. 2007). Climate Climate-induced human population displacement is likely to be a major source of future conflict (Urdal 2008). Therefore, it is important to begin quantifying indices of climate parameters that are favorable to human settlement so that we may begin to make projections about how human populations may shift spatially in response to predicted climate changes.

www.ethiopianreview.com/content/8897

Ethiopian Human Population Distribution

Previous studies have indicated that climate due to orographic effects has been a major driver of human settlement distribution in Ethiopia since at least 700 B.C.E. (Clegg et al. 1972, Roundy 1976, Egziabher 1998, Nyssen et al. 2004). Although many other social, political, and historical factors influence the complex decision-making involved in where people settle, there is general acceptance that in Ethiopia certain elevation zones are more preferable dwelling places because of their favorable climates. Early settlements tended to occur in narrow alluvial valley bottoms, and from there human activity spread to steeper slopes and into the highlands, where agriculture and pastoralism became dominant livelihood practices (Nyssen et al. 2004).

Most of Ethiopia’s human population is distributed throughout the Afro-alpine and Afro-montane elevation zones. The Afro-alpine zone is characterized by regions higher than 3200 meters in elevation. In this zone, human population densities are typically low, and livestock grazing is the most important livelihood activity (Egziabher 1988). Since the mountains attract precipitation, moisture is generally not a limiting factor to plant growth. However, intense solar radiation drives high rates of evapotranspiration from vegetation, contributing to these plants’ low growth rates and productivity. As a result, agriculture as a primary livelihood practice is not feasible in the Afro-alpine zone (Egziabher 1988). In contrast, the Afro-montane zone ranges from about 900 to 3200 meters in elevation, and its land use is dominated by rain-fed agriculture (Egziabher 1988). In the northern and eastern regions of this zone, mixed cereals predominate, while root crops are more typically grown in the western and southern regions. According to several studies, Ethiopians have historically considered the healthiest elevation zone to lie between about 1800 and 2400 m (Clegg et al. 1972, Roundy, 1976).

While some elevations are considered favorable because of the livelihood practices that are possible under their associated climates, other regions are unfavorable because their climates are conducive to diseases, such as malaria, yellow fever, trypanosomiasis, and schistosomiasis. Currently, these diseases tend to have upper altitude limits ranging from 550 to 2000 m, beyond which temperatures and surface water availability limit vector survival (Roundy 1976, Tanser et al. 2003). Ethiopians recognize that zones lower than 1600 m are often undesirable as permanent settlements because of their hazards of fevers and malaria (Harrison et al. 1969, Roundy 1976). River valleys are also often avoided during and after the rainy season, when environmental conditions become more conducive to disease transmission (Roundy 1976).

http://www.worldpress.org/Africa/2293.cfm

Although living at high elevations has associated risks, such as hypoxia and hazardous pregnancies, these negative effects are much milder than those associated with disease incidence at lower altitudes (Harrison et al. 1969, Clegg et al. 1972). As malaria and other disease vectors are predicted to respond to changing climate by moving into previously malaria-free highland areas by the 2050s (Tanser et al. 2003), human populations may correspondingly shift to higher elevations. Human physiological research indicates that lowland inhabitants moving into higher elevation zones would not necessarily experience adverse altitudinal affects on their development and health. In studies of presumably homogenous genetic populations in Ethiopia, people growing up in the highlands were, by some metrics, healthier than their lowland counterparts (Harrison et al. 1969, Clegg et al. 1972). Therefore, when considering how human populations will shift spatially in response to climate change, vertical movement to higher elevations may be a major trend.

Analytical Approach

Because the literature indicates that human settlement locations in Ethiopia are influenced substantially by climate (Clegg et al. 1972, Roundy 1976, Egziabher 1998, Nyssen et al. 2004), we used a multiple linear regression approach to determine the relationships between climatic and topographic factors and current human population density distributions (Guisan and Zimmermann 2000). Such relationships were estimated by parameterizing a multiple regression model using current population density data from 2000 as a dependent variable and a suite of current climate condition variables (average of BIOCLIM climate variables from 1950-2000) as the explanatory variables. The model that we developed was then applied to future climate scenarios in 2020 and 2050 to estimate the likely distribution of humans under those projected conditions. This allowed us to identify the environmental (climate) factors that best predicted areas of population density when the model was fitted to modeled climate scenarios.

Unfortunately, due to a general paucity of quality demographic data available for Ethiopia, we were limited in our modeling capabilities to using primarily climate data in our predictions, but it is highly unlikely that climate alone can sufficiently explain human population trends. In addition, we draw attention to the caveat that true population models must approach modeling using available time series data. In this regard, our model is not taking into account current population trends (and it is not possible given the limitation of data available) but rather is providing a predictive surface over the geographic area of Ethiopia of where populations might be expected to occur based on climate patterns alone. Nonetheless, we feel that climate conditions are still very important determinants in human density distributions due to climate's wide-ranging impacts on habitat conditions, such as agricultural land cover types. Although we are limited in our predictive abilities using climate as primary explanatory variables, generalizations can still be drawn from our model which can identify areas likely to undergo human population change based on climatic conditions.

Disclaimer: The content of this webpage and results are not to be used in any context relating to scientific communication or inference on Ethiopian populations. This analysis has not been subject to any peer review by qualified scientists and thus is not suitable as a reference for any material.