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IMPACTS OF URBANIZATION AND CLIMATE CHANGE ON THE HYDROLOGICAL CYCLE: A STUDY IN MODERN AND ANCIENT LAND USE CHANGE
Abstract
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.
Table of Contents
List of Figures vii
List of Tables xii
Acknowledgments xiii
Chapter 1 Introduction 1
Chapter 2 Models and methods 9
2.1 PIHM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Basic parameters . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.2 LAI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Macropore algorithm and soil degradation . . . . . . . . . . . . . . 16
2.2.1 Macropore effect in PIHM . . . . . . . . . . . . . . . . . . . 18
2.3 Land use change model . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3.2 Land use and urban land demand . . . . . . . . . . . . . . . 24
2.3.3 Land use change Method . . . . . . . . . . . . . . . . . . . . 25
2.3.4 Result and discussion . . . . . . . . . . . . . . . . . . . . . . 32
2.3.4.1 Model performance evaluation . . . . . . . . . . . . 32
2.3.4.2 Land use change from 2001 to 2101 . . . . . . . . . 35
2.3.4.3 Land use change from the 1900s to 2006 . . . . . . 37
2.3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Chapter 3 Simulation of past, present and future land use change
on catchment hydrology: the Conestoga Watershed 44
3.1 Research area and background . . . . . . . . . . . . . . . . . . . . . 44
3.2 Geospatial data sources . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.2.1 Scenario development: past, present and future . . . . . . . 49
3.3 Model parameterization . . . . . . . . . . . . . . . . . . . . . . . . 51
3.4 Results analysis and discussion . . . . . . . . . . . . . . . . . . . . 54
3.4.1 Stream flow simulation for three LUC scenarios . . . . . . . 54
3.4.2 The spatial distribution of water storage . . . . . . . . . . . 59
3.4.3 Water balance . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3.4.4 Budyko Curve . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Chapter 4 Dynamic Land use and climate change in the Con-
estoga watershed 69
4.1 Data and Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.2 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.2.1 Stream flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.2.2 Ground water . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.2.3 Water balance . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Chapter 5 The Implications of Land Use, Climate and Hydrologic
Change on the Ancient Maya City of Tikal 85
5.1 Research Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.2 Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
5.3 Population-driven land use change . . . . . . . . . . . . . . . . . . . 94
5.3.1 LUC trend in Tikal . . . . . . . . . . . . . . . . . . . . . . . 98
5.4 Result and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.4.1 Stream flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.4.2 Water balance . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Chapter 6 Summary and future work 117
6.1 A story of two urban centers: modern and ancient . . . . . . . . . . 117
6.2 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
6.3 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Bibliography 123
Chapter 1 |
Introduction
Hydrologically speaking, the general literature on land use change (LUC) suggests that urbanization and agricultural land development increase the impervious area, decrease natural infiltration, reduce water storage capacity, increase overland flow, contribute to soil, stream and groundwater contamination, significantly alter evapotranspiration, and generally change the water balance locally and at the watershed scale (Boggs and Sun, 2011; Bronstert et al., 2002; Chang, 2004; FISRWG, 1998). LUC seems to have both direct (water balance) and indirect (ecosystem services) influences on the hydrological processes operating on the catchment. At the same time, climate change is clearly the focus of the world science community as it is projected to have extreme effects on water supplies, floods, drought, water quality and ecosystems. However, the relative impact of land use change and climate change together as they impact the local water cycle is still unknown. Does climate change reinforce the drivers of LUC or are there compensating impacts? Or does LUC reinforce drivers of climate change (e.g., increasing temperatures leading to longer and deeper drought)? Questions like these must be addressed if we are to improve our response to the inevitability of change itself.
In the past century, dramatic changes have occurred in the world. By the middle of 2009, the world entered in global urban era as more than half of world population lived in urban rather than rural area (United Nations, 2009). By the end of 2016, urban population grew to ∼54.5% (United Nations, 2009). Technological innovation modernized agricultural production leading to greater efficiencies and industrial farming. Industrial development encouraged migration of people to urban centers (O’Driscoll et al., 2010; Srinivasan et al., 2013). In United States (US), Urban population grew from ∼70% at 1960 to ∼82% at 2016 (United Nations, 2009). More and more evidences indicate that human activities have raised the level of green-house gases in the atmosphere, which causes the global warming. More specifically, climate change has already intensified severe weather, which causes great loss of human life and wealth. Climate change refers to the variability of meteorologic variables, as well as to the statistical change in mean, that may last for longer or shorter periods (IPCC, 2014). Human activities are not the sole forces of climate change. Internal forces of climate change, such as the modulations of the solar cycles and volcanic eruptions, also exert inherent perturbation on the energy balance of the atmosphere.
While humans have been busy exploiting the Earth’s resources and disposing residuals such as gaseous, effluent and solid waste, global environmental and climatic change has put more stress on human health, economy and society. When we think of possible futures for human society, we must consider the vulnerability and resilience of natural systems and adaptiveness of human agency. IPCC (2014) gave the well-accepted definition of resilience, vulnerability and adaptation.
Resilience is “the capacity of … systems to cope with a hazardous event or trend or disturbance, responding or reorganising in ways that maintain their essential function, identity, and structure, while also maintaining the capacity for adap-
tation, learning, and transformation”. Vulnerability is defined as“the propensity or predisposition to be adversely affected. Vulnerability encompasses a variety of concepts and elements including sensitivity or susceptibility to harm and lack of capacity to cope and adapt.” Adaptation is “the process of adjustment to actual or expected climate and its effects. In human systems, adaptation seeks to moderate or avoid harm or exploit beneficial opportunities. In some natural systems, human intervention may facilitate adjustment to expected climate and its effects.”
It is the hypothesis of this dissertation that understanding the impact of historical land conversion on present day hydrological processes through the use of spatially explicit watershed modeling is the key to assess, attribute and predict the relative impacts of urbanization, deforestation, agricultural and industrial development on the catchment water resources, ecosystem services and catchment scale hazards from drought and flooding. Likewise the same approach applied to assess the impacts of climate change, offers the prospect of resolving the competing and/or compensating impacts of climate and LUC.
In this study we apply the Penn State Integrated Hydrologic Model (PIHM)
to partition the water balance in space and time over two urban catchments, one modern and one ancient. The goal is to assess the role of hydrologic change in urbanizing watersheds and to evaluate the contemporaneous impacts of climate change. It also seems reasonable to consider the drivers of change and to model them in a way that interacts or is coupled to the hydrologic system.
Clearly, population growth is one of the major drivers, or is at least correlated with land use change both in the past and at the present. As such the study attempts to find connections of population growth and land use change that can be described in relatively simple models and that use similar kinds of geospatial data as are used in developing catchment hydrologic models. This study takes a spatially distributed modeling approach to produce place-based land use scenarios, as a means of evaluation and attribution of future hydrological change from climatic and land use changes.
Consider our watershed as a system in dynamic equilibrium. At the beginning, the natural system is a lightly settled human environment that is both stable and sustainable. As population grows, human technologies enhance the ability to harvest resources, which gradually degrades the original environment through disposal of gaseous, liquid and solid waste. The deteriorating environment may have negative consequences to human society and makes us question our anthropological achievements. Both resilience of the environment and adaptiveness of human society are necessary to assure a measure of quality and avoid catastrophic failures. Adaptation will require scientifically-grounded interventions based on our best knowledge and best practices.
This research does not intend to assess global or top-down changes in the humanclimate environment but rather proposes a modest bottom-up effort to advance our understanding of LUC and climate change at the watershed scale, a scale where real problems emerge and the potential for problem solving seems reasonable. The study will appraise the vulnerability of the water cycle in two specific cases, one ancient and one modern, one retrospective and one prospective.
It is at the watershed scale where human activities alter the land cover and land use and where present and future climatic inputs have unresolved impacts. The hope is to begin to develop an integrative approach to assess and attribute the degree of adaptiveness and sustainability of a local population under stress from the past, present and future environmental and climatic change on water supplies.
Hydrological changes in a watershed are the product of non-linear combinations of physical properties and climatic forces, and may lead to unanticipated consequences to the larger human society (e.g. Flint, Michigan drinking water lead crisis).
