Author ORCID Identifier

Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Agriculture, Food and Environment


Agricultural Economics

First Advisor

Dr. Sayed H. Saghaian

Second Advisor

Dr. Michael R. Reed


Nowadays, the large scale of migratory movements caused by violence, poverty or climate change have made topics related to this worldwide diaspora a vanguard of research on international development. For one thing, the so-called “caravan migrants” that traveled from Central America in search for a better life in the U.S. have been blocked at the U.S.-Mexico border while U.S. agricultural sectors that are labor-intensive, such as the sectors of fruits and vegetables where most illegal immigrant farmworkers are hired, have been suffering from the shortage of farm labors for years. Such a situation calls for a development of U.S. immigration laws and policies. On the other hand, years of armed conflict in the Middle East and North Africa result in a large number of refugees moving to the heart of Europe and directly lead to the European migrant crisis. Whether those refuges are good or bad for a host country’s economy is an urgent question that should be answered without delay. Lastly, people in least developed countries (LDCs) are forced to leave their traditional habitats for improving the quality of life in host countries due to climatic factors that jeopardize their existence in their home countries. Those who are unable to afford the migration cost are trapped in poverty. How to weaken the “climate-migration poverty trap” is thus an issue that needs to be addressed as soon as possible.

This dissertation consists of three essays respectively regarding the three issues mentioned above. To begin with, the division of opinions on the U.S. Real ID Act that has restricted many illegal immigrants from working allows essay one (Chapter 2) to employ a difference-in-differences (DID) method to estimate the impact of the Act implementation on U.S. fruit and vegetable sectors that are labor-intensive. A hypothesis is made to pre-suppose that the impact is negative and then a hypothesis test is conducted for verifying if the hypothesis should be rejected or not. Empirical results are in general consistent with the hypothesis and suggest a way of legalizing those illegal immigrant farmworkers.

Essay two (Chapter 3) estimates the relationship between Germany’s refugee stocks and its exports to and imports from the home countries where the refugees originate. This analysis assumes that Germany’s refugee stocks are positively correlated with its exports to and imports from those home countries given lenient immigration policies towards refugee immigrants in Germany. It then conducts an estimation to test the hypothesis by using a gravity model with a Poisson Pseudo-Maximum Likelihood (PPML) estimator. Empirical results are not consistent with the hypothesis but suggest that Germany’s refugee immigrants may be not yet capable of exerting remarkable pro-trade effects.

Essay three (Chapter 4) quantifies the impacts of three adaptation means (more access to irrigation, less CO2 emission and larger amount of foreign direct investment (FDI)) on the migration rate for 23 LDCs of origin with respect to 129 countries of destination. This analysis assumes that the three adaptation means are effective measures for LDCs in response to high temperatures that reduce agricultural yields and that they function as promoters that facilitate climate-induced migration. Data used in this essay are cross-sectional, so solving the problem of heteroscedasticity and endogeneity by using generalized method of moments (GMM) is necessary to ensure that the estimates are not biased. Empirical results are consistent with the hypothesis, suggesting that the three adaptation means are promising ways of weakening the “climate-migration poverty trap”.

Overall, the dissertation conducts estimations based on hypothesis tests. It provides planners and policy makers with evidence regarding the economic contributions that immigrants bring for a host country and sheds light on the measures of dealing with the global issue of immigration.

Digital Object Identifier (DOI)