Evaluating Hydrological Response to Forecasted Land-use Change: Scenario Testing in Two Western

U.S. Watersheds

William Kepner1, Darius Semmens2, Mariano Hernandez3 and David Goodrich3

1. US Environmental Protection Agency2. US Geological Survey3. USDA, Agricultural Research Service

Introduction• Alternative Futures is an

approach to represent the impact or benefits of decisions and policy in future scenarios

• It can be provide information which can be used to assess potential changes of the landscape relative to human use

• It can provide options that could be useful for sustainable mgt. and thus minimize impacts for future generations

Geographically-based Ecosystem Services Conceptual Approach

1) Service identification2) Scenario development

• Stakeholder engagement3) Ecosystem goods and services assessment

• Baseline and scenario assessments (e.g. water provisioning)

4) Valuation5) Integrated risk assessment

• Analysis and reporting of comprehensive scenario impacts & tradeoffs

6) Risk management• Working with stakeholders to identify

management solutions

PREMISE:PREMISE:

Envisioning needs to be a critical part of Envisioning needs to be a critical part of both science and social decisionboth science and social decision--making making with the purpose of creating a shared with the purpose of creating a shared common vision for both a desirable and a common vision for both a desirable and a sustainable future.sustainable future.

QUESTION:QUESTION:

How do changes in land use, and any How do changes in land use, and any subsequent change to land cover, affect subsequent change to land cover, affect hydrologic and ecological conditions and hydrologic and ecological conditions and what are the tradewhat are the trade--offs between offs between management decisions?management decisions?

Analyzing Consequences of Future EnvironmentsAnalyzing Consequences of Future Environments

Ecosystem Services

Human Needs

Find and Maintain a Balance

Alternative Futures & Landscape Change

38

1021

10937

35

8

-2429

79

47

21

1

528

12

9

13

7

10

33

11

828

15

9

1652

-6

6

33

16

15

114

3

2

13

41

4

10

28

6

30

60

56

39

17

46

15

-5

6

Projected State Population Percent Change: 2000 to 2030

Source: U.S. Census Bureau, Population Division,Interim State Population Projections, 2005

San Pedro Valley, AZ near U.S./Mexico Border

Yuqiong Liu et al. 2008. Formal Scenario Development For Environmental Impact Assessment Studies In "Developments in Integrated Environmental Assessment, Elsevier.”

Scenario Development and Analysis

1. Scenario Definition• Stakeholder focus group meetings to

determine user preferences for alternative management options;

2. Scenario Construction• Model future land cover & hydrology based

on stakeholder input & system conceptualization;

3. Scenario Analysis• Comparison of scenario results relative to

baseline conditions (change analysis);

4. Scenario/Risk Assessment• Identify socio-economic, institutional, &

environmental dimensions• Visualization & presentation of results;

5. Risk Management• Decision makers choose course of action.

San Pedro (Stakeholders, Researchers, & Decision-makers)

Steinitz et al. 2003. Alternative Futures for Changing Landscapes, The Upper San Pedro River Basin. Island Press.

Future Urbanization Change Scenarios for Upper San Pedro River (2020).

1. CONSTRAINED (CONSERVATION) – Assumes population increase less than 2020 forecast (78,500). Development in existing areas, e.g. 90% urban.

2. PLANS (TREND) – Assumes population increase as forecast for 2020 (95,000). Development in mostly existing areas, e.g. 80% urban and 15% suburban. Assumes existing comprehensive land-use plans are implemented as written, with few exceptions, and recent trends (e.g. population) continue.

3. OPEN (DEVELOPMENT) – Assumes population increase more than 2020 forecast (111,500). Most constraints on land development removed. Development occurs mostly into rural areas(60%) and less in existing urban areas (15%).

Steinitz et al. 2003. Alternative Futures for Changing Landscapes, The Upper San Pedro River Basin. Island Press.

San Pedro General Conceptual Model(based on Havstad et al., 2007)

Semi-Arid Watershed

ET Infiltration Runoff

Surface WaterShallow Deep

Consumptive Uses

Plant Growth & Composition

Soil Erosion

Ground Water

Agricultural Production

IndustrialProduction

ResidentialConsumption

Water Quality Air Quality

Recreation

UrbanLandscaping

Wildlife Habitat

Microclimate Modification

Provisioning

Supporting

Cultural

Regulating

Disturbance Factors

or Stressors

Urbanization, Climate, Fire, Grazing,

etc.

Herbivore Production

BiodiversityConservation

Wildlife Habitat

CarbonSequestration

Fisheries

Watershed Discretization(model elements) ++

LandCover

Soils

Rain (Observed or

Design Storm)

Results

Run model and import results

Intersect model elements with

Watershed Delineation using Digital Elevation

Model (DEM)

Sediment yield (t/ha)Sediment discharge (kg/s)

Water yield (mm)Channel Scour (mm)

Transmission loss (mm)Peak flow (m3/s or mm/hr)

Channel Disch. (m3/day)Sediment yield (kg)

Percolation (mm)Runoff (mm or m3)

ET (mm)Plane Infiltration (mm)

Precipitation (mm)Channel Infiltration (m3/km)

SWAT OutputsKINEROS Outputs

AGWA Conceptual Design: Inputs and Outputs

Output results that can be displayed in AGWA

• There is considerable variation – particularly between extremes produced by constrained and open scenarios. Assessment unit = 68 subwatersheds

• Surface runoff will increase in all three scenarios

• Sediment yield will increase with increasing surface runoff

• Changes in channel flow are a proxy for riparian impact, and can guide targeted monitoring and mitigation plans

Scenario Analysis – Relative Change

Model Simulation Results

Average daily value change over 20 years

1,1261,0811,0881,042Sediment Yieldt/day

40,77441,48341,59342,760Percolationm3/day

199,325193,364194,573186,538Surface Runoffm3/day

2020 Open

2020 Plans

2020 Constrained

2000 Baseline

Some General Study Conclusions

• All 3 scenarios produce a generally negative set of impacts as a result of predicted urbanization;

• There is considerable spatial variation across the basin and between the 3 scenarios– particularly between extremes produced by the Constrained and Open options;

• The Open (Development) scenario demonstrates the greatest increase in surface runoff, flow discharge and sediment yield, especially in the downstream reaches;

•Percolation, and thus groundwater recharge, will be most reduced under the Open scenario;

•All changes in hydrological response likely due to land cover change associated with replacement of vegetated surfaces to impervious surfaces (urbanizing environment).

Cont’d

Some Future DirectionsHow do changes in land use and any subsequent change to land cover affect the hydrologic and ecological conditions and what is the economic value of these impacts?

What are the spatial and temporal patterns of LU/LC that maximize the environmental and economic value of (selected) ecosystem services?

Stakeholder Engagement & Dialogue

Scenario Construction

Biophysical/Hydrological Modeling

Economic Models & Analysis

Ecosystem Service Maps & Analysis

Non-market Valuation & Tradeoff

Some concluding remarks• The developed methods provide the potential to

assess the spatial and temporal changes in land cover at a landscape or watershed scale.

• Specifically, they provide an ability to characterize large assessment areas and provide a comparative mechanism to visualize and understand results across scientifically and socially meaningful assessment units, i.e. watersheds/subwatersheds.

• Collectively, the combination of technology and the decision analysis framework provide an improved ability to understand the conditions of current and past environment and provide a better predictor for consequences of future actions.

THANK YOU-

William Kepner, Darius Semmens, Mariano Hernandez, and David Goodrich