Urbanization Impacts on Surface Runoff. of the Contiguous United States

Transcription

1 Urbanization Impacts on Surface Runoff of the Contiguous United States Presenter: Jingqiu Chen Co-authors: Lawrence Theller, Margaret W. Gitau, Bernard A. Engel 07/13/2016 1

2 Presentation Outline Motivation Introduction Methods and Materials Results and Discussion Conclusions 2

3 Motivation Unprecedented Urban Growth 3

4 Motivation Lijiang, CHINA Photo source: UN-HABITAT Africa Source: nization-rates-africa/ Paris, FRANCE Source: interiordesignschooldaily.com Land surface modifications Changes in water supply Urbanization Water quality degradation Changes in water demands 4

5 Introduction Every urban area in the United States has expanded substantially in area in recent decades (USEPA, 2013). Developed land in the contiguous U.S. increased in area by 20,296 km 2 from 2001 to 2011 (NLCD). Chicago Downtown, USA (public domain) Research related to urbanization impacts on surface runoff has focused on changes at the watershed scale. However, quantitative assessment at a national scale is scarce. Research Question: How has urbanization impacted surface runoff on a national scale? 5

6 Methods and Materials Computer-based hydrological model The Long-Term Hydrologic Impact Assessment (L-THIA) Model Approach: SCS CN method The L-THIA model (Lim et al., 2006) The L-THIA Tabular Tool A six-digit combination raster layer An external component (a Java program) calculates daily runoff for all curve numbers 6

7 Methods and Materials Example of the six-digit combination raster layer in the L-THIA Tabular Tool Land use index in NLCD Urban land types in NLCD Six-digit combinations 21 Developed Open Space Developed Low Intensity Developed Medium Intensity Developed High Intensity Note: the first digit represents hydrologic soil group, A=1, B=2, C=3, and D=4; the second to third digits represent the urban land index in NLCD, 21 = Developed open space, 22 = Developed low intensity, 23 = Developed Medium Intensity, and 24 = Developed high intensity; the last three digits represent SCS CN value, those values are based on USDA NRCS (NRCS, 1986). 7

8 Methods and Materials The release of National Land Cover Database (NLCD) 2011 edition datasets for 2001, 2006, and 2011 across the nation makes the assessment of land use change impacts on surface hydrology at the national level feasible. Input Data: Soil Land use Precipitation The State Soil Geographic (STATSGO) dataset (Wolock, 1997) The NLCD 2001, 2006, and 2011 CLIGEN (climate generator) 50 years Daily precipitation for each of 2,600 weather stations 8

9 Methods and Materials The L-THIA Tabular Tool was set up based on U.S. county boundaries (a total of 3,109 counties (48 states and D.C.), and the average annual runoff was calculated only from pixels belonging to urban land. The normalized average annual runoff depth (NAARD) from urban land (county and state) National average annual urban runoff volume increase due to urbanization Whether population change is a consistent indicator for urban development U.S. Census Bureau 2001, 2006, and

10 Results and Discussion 1. Assessment of NAARD by Counties in the Contiguous U.S. NAARD Statistics and distribution in 2001 County-based NAARD maps of contiguous U.S. in 2001, 2006, and

11 Results and Discussion 1. Assessment of NAARD by Counties in the Contiguous U.S. Red line: mean Dash line: Standard deviation (SD) Blue line: Classification line <0.5SD of NAARD in 2001: green 0.5~1.5 SD of NAARD in 2001: yellow 1.5~2.5 SD of NAARD in 2001: orange >2.5 SD of NAARD in 2001: red NAARD Statistics and distribution in 2001 County-based NAARD maps of contiguous U.S. in 2001, 2006, and

12 Results and Discussion 2001 to Categories Change Percentage (%) to Assessment of NAARD by Counties in the Contiguous U.S to 2011 Green Yellow Orange Red urbanization occurred nonhomogeneously across the contiguous U.S. from 2001 to urban expansion and intensification serve as driving forces altering surface runoff, resulting in more medium and very high runoff counties. County-based NAARD maps of contiguous U.S. in 2001, 2006, and

13 Results and Discussion 2. NAARD, Urban Land, and Population of Counties with Very High Urban Runoff Increasing Percent (%) from 2001 to Fort Bend, TX Fredericksburg city, VA Collin,TX Bexar, TX Manassas Park city, TX NAARD Population Urban Land Cobb, GA County Mecklenburg, NC Population is not a consistent factor stimulating urban development. Tarrant, TX Orange, FL Galveston, TX Change percentage of NAARD, population, and urban land from 2001 to 2011 of top ten counties with very high urban runoff Percent Change (%) from 2001 to Orleans, LA Wayne, MI Martinsville city, VA St. Louis city, MO NAARD Population Urban land Cuyahoga,OHHampton city, Jefferson, LA VA County Portsmouth city, VA Newport, RI Cook, IL Change percentage of NAARD, population, and urban land from 2001 to 2011 of some counties with very high urban runoff 13

14 Results and Discussion 3. Assessment of NAARD by States in the Contiguous U.S. NAARD (mm) DC RI FL NJ MA CT LA DE MD MS Top ten NAARD values states Urban Land Percent Change (%) to to to 2011 DC RI FL NJ MA CT LA DE MD MS Top ten NAARD values states Population Percent Change (%) to to to 2011 DC RI FL NJ MA CT LA DE MD MS Top ten NAARD values states The top ten NAARD states are mainly distributed in the northeast, east, southeast, and southern United States. Their NAARD values were jointly influenced by high precipitation and increasing urban land. 14

15 Results and Discussion NAARD (mm) 3. Assessment of NAARD by States in the Contiguous U.S AZ UT NV CO SC GA ID WY NM NC Top ten NAARD change percentage states Urban Land Percent Change (%) to to to 2011 AZ UT NV CO SC GA ID WY NM NC Top ten NAARD change percentage states Population Percent Change (%) to to to 2011 AZ UT NV CO SC GA ID WY NM NC Top ten NAARD change percentage states The top ten NAARD change percentage states in 2011 were mainly distributed in the western U.S. that has low precipitation, and their NAARD values were mainly influenced by high increases in urban land 15

16 Results and Discussion National average annual urban runoff volume increase due to urbanization Average Annual Urban Runoff Volume Increases (m 3 ) Billions to to to 2011 Net Gain Area (km 2 ) to to to 2011 Developed Open Space Developed Low Intensity Urban Land Developed Medium Intensity Developed High Intensity Urban land change between 2001, 2006, and 2011 for the contiguous U.S. (Data source: Homer et al., 2015) 16

17 Conclusions: (1) The majority of counties in the contiguous U.S. could be categorized as low urban runoff counties that had NAARD from urban land less than 17.8 mm. (2) Urban expansion and intensification resulted in more medium and very high urban runoff counties. (3) NAARD values of the top ten NAARD states in 2011 were jointly influenced by high precipitation and increasing urban land, while the top ten NAARD change percentage states in 2011 were mainly distributed in the western U.S. that has low precipitation, and their NAARD values were mainly influenced by high increases in urban land. 17

18 Continued: (4) Nationally, about 3.3 billion m 3 of urban runoff were gained due to urbanization from 2001 to (5) Population increases can stimulate urban development. However, some areas have undergone decreasing population but increasing urban land. Therefore, only considering population change is not sufficient to analyze the increase in urban development. 18

19 Thank you! Questions and Comments? 19

20 Preliminary Assessment of Land Use/Land Cover Change Impacts on Surface Runoff (16 land use types from the NLCDs) The outliers with respect to percentage change in average annual runoff depth (AARD) showed no pattern, and some of them were reversed between the two five-year periods. County based outlier of AARD change percentage 20

21 Land use/land cover change of counties belonging to outliers with increasing AARD from 2001 to