Impacts of Urbanization and Climate Change on the Hydrological Cycle: A Study in Modern and Ancient Land Use Change


The past one hundred years have seen a tremendous migration to towns and cities worldwide. This population movement exerts serious impacts on surface and ground-water supplies, soil health, and the sustainability of ecosystems. At the same time, climate change has become a decisive influence on water systems as land conversion continues. Historically, urbanization and climate change were two important determinants in the sustainability of water, food and energy supplies, as well as the increasing risk of environmental hazards. At the watershed scale the evolving land use change in urban areas does not only change the flood risk because of increasing impervious areas or by directly reducing the consumption of water by trees and plants, but also fundamentally alters the local water balance and the partitioning of water within the land-atmosphereecological system. Both land use change and climate change may influence the urban watershed in ways that reinforce or compensate sustainable management. In this study we applied two spatially explicit models to the problem. One is the Penn State Integrated Hydrologic Model (PIHM), a hydrologic model that partitions the water balance in space and time over the urban catchment. The other is the Cellular Automata Land Use Change Model (CALUC), a land use change model, which simulates the evolution of land use classes based on physical measures associated with population change and land use demand factors. We selected two study sites, one modern and one ancient, to highlight the capability of coupling catchment hydrology with land use change models. The goal is to assess the role of hydrologic change in urbanizing watersheds and to evaluate the contemporaneous impacts of climate change. The modern sites are the Conestoga watershed and the Lancaster PA urban center; the historical site is the ancient Maya city of Tikal in Peten region of Guatemala. In each setting, the essential data was developed and the models were used to evaluate how urbanization and land use change gradually altered the entire water balance often in unexpected ways. Chapter 1 introduces the overall problem and carries out a comprehensive literature review for each of the following chapters. Chapter 2 discusses the relevant models used in the study, and the role of model parameterization, particularly the important role that macropores have on maintaining a healthy soil and supporting soil moisture and recharge to groundwater. Chapter 2 also describes the Cellular Automata Land Use Change model, which is adopted here to simulate land use conditions. Chapter 3 then evaluates the past, present and future land use conditions in the Conestoga watershed and develops quantitative metrics of evaluation. Chapter 4 extends the Conestoga case study to evaluate hydrologic performance when dynamic land use and future climate change scenarios from IPCC are the drivers. An evaluation of the relative importance of land use and climate to hydrologic change is presented. Chapter 5 implements the models in a retrospective scenario of the water history of the ancient Maya city of Tikal and discusses the problem of urbanization-deforestation-agriculture land conversion, and the likely sensitivity of their water supply to extreme climate events. Chapter 6 summarizes the two case studies and makes inferences on the resilience and elasticity of the two study sites to climate and land use change.

Ph.D Dissertation,