## 1 Introduction  
During the 20 th century, the world population increased from 1.65 billion to six billion [1]. The world population is currently growing by approximately 74 million people per year, with most growth occurring in developing countries [2]. Much of the focus of the population-environment literature is on how population growth impacts the environment [3; 4; 5]. Specific focus areas include the effects of population dynamics on environmental degradation [6], water resources [7], deforestation [8], and food security [9]. However, few studies have investigated how environmental change influences demographic processes [10; 11; 12]. This study aimed to contribute to the literature on this topic. Recent research illuminated the ways in which a number of population variables, such as age and sex composition, household demographics, and the elements and processes of the population balancing equation, are related to environmental change [3]. Some research found a reciprocal relationship between population dynamics or development and environmental change [3]. Population redistribution is driven by social, economic, geographical, and environmental factors in complex ways, making it very difficult to predict outcomes [13]. Economic development ([14], industrialization and urbanization [15], education [16], and environmental change [3] all influence population redistribution. For some countries, especially countries with rapid economic growth, population redistribution caused by environmental change is often masked by a variety of socio-economic factors. Identifying the relationships between population redistribution and environmental variability and change is a challenging task. Under the background of global climate change, the relationship between environment and population redistribution attracted extensive attention [17]. Climate change has observable effects on the environment and has the potential to impose additional pressure in some regions [18]. Climate change is recognized as a \"threat multiplier\" that compounds the difficulties currently facing developing countries [19; 20]. Some environmental factors driven by climate change were shown to affect population redistribution, but the effects are often non-linear [21; 22]. Environmental change includes not only slow processes, such as changes in precipitation or temperature [23], but also rapid, extreme events, such as extreme wet and dry events [24]. Some studies found that it has a different response of population spatial movement for these two different categories of environmental changes. Slow environmental change may lead to population migration [25], whereas sudden natural disasters or extreme events are more likely to cause temporary displacement [12]. In this paper, we estimate the contributions of changes in water availability and agricultural crop yields to past changes in population distribution. We select Mexico and Ethiopia as study cases for a few reasons. Firstly, Mexico and Ethiopia are both developing countries, but the former is an upper-middle-income economy, whereas the latter is a low-income economy [26]. In addition, these countries represent contrasting cases in terms of dependence on agriculture; Mexico has 13% of its population working in the agricultural sector and obtains 4% of its gross domestic product (GDP) from agriculture, whereas, for Ethiopia, the corresponding percentages are 73% and 37% [26; 27]. Secondly, these two countries have moderate population sizes and land areas relative to world averages, lending them a certain amount of comparability. Thirdly, they are both low-latitude countries. A growing body of evidence shows that low-latitude countries will experience the greatest impacts from global warming [28]. Finally, regardless of the differences in overall income between the countries, both have large proportions of their populations living in poverty, and poor populations are generally more vulnerable to the effects of climate change than wealthier populations [29].