Motivation

Western US-Mexico Border Region

Similarities across the border

• Arid climate with highly variable precipitation

(Fig. 1a)

• North American Monsoon is a major source of

surface water

• Rapidly growing population

• Cities, irrigated agriculture, and livestock

raising (Fig 1b) all compete for scarce water

resources

Differences

• Wealth (GDP per capita, 2014 $USD)

• US: $55,000/y

• Mexico: $10,000/y

• Water policies

• US: better monitoring; pay by volume

• Mexico: poor monitoring; agricultural users

pay flat annual fee

Land Surface Model:• Variable Infiltration Capacity (VIC) release 4.2 (Fig. 2)

• Added irrigation scheme of Haddeland et al. (2006)

• New clumped canopy scheme that allows for soil evaporation in spaces

between plants in sparsely-vegetated biomes (Bohn and Vivoni, 2016)

(Fig. 3)

• Driven by gridded meteorology of Livneh et al. (2015)

• Vegetation parameters (LAI, canopy fraction, albedo) derived from

MODIS observations 2000-2012

Analysis Tools: Modeling and Remote Sensing Data

Land Cover/Use Changes and their Socio-Economic Drivers, 1993-2011

Major Trends:

• Expansion of croplands in Mexico, particularly NE Chihuahua (1) and Sinaloa and S Sonora (2); these are primarily

horticulture (fresh fruits and vegetables) for export to the US, and alfalfa (for cattle feed)

• Reduction of croplands in W Sonora (3) due to groundwater overexploitation

• Reduction of croplands in central Arizona (4) due to urbanization

1. Changes in cropland area

2. Changes in pasture area

Impacts on Irrigation, 1993-2011

Major trends:

• Increases in irrigation usage in NE Chihuahua (1) and Sinaloa and S. Sonora (2) of 100-200 mm/y

• Increases consist almost entirely of groundwater extraction (fruits, vegetables, and alfalfa)

• Declines in irrigation in W. Sonora (3) due to aquifer overexploitation and saltwater intrusion

• Decline in irrigation usage in central Arizona (4) due to conversion of croplands to urban

Implications for Sustainability and Future Work

NAFTA has placed increasing pressure on Mexico’s overexploited aquifers

• NAFTA has enabled the growth of export-oriented agricultural and pastoral industries in

northern Mexico

• These industries are both water-intensive and best-suited for customizable

groundwater extraction

• Because of Mexico’s lax agricultural water policies, Mexican farmers have a

comparative advantage, particularly near the US border

• This has encouraged increased groundwater extraction near the US-Mexico border,

increasing pressure on many of Mexico’s overexploited aquifers (Fig. 9)

• Aquifers in W. Sonora have already failed

Future Work

• Assess impacts on streamflows, surface temperatures

• Estimate virtual water transfers between the US and Mexico

• Compare values of commodities and water

References

Science QuestionsOverarching Question: How have changes in land cover and use in the post-NAFTA period altered the hydrology of the

US-Mexico border region?

Subsidiary Questions:

1. Which changes in land cover and use have had the biggest impact on hydrology and water resources?

2. What were the major socioeconomic drivers of these changes?

3. What are the implications for sustainability in the future?

Figure 2. VIC large-scale hydrology model.

Land Cover MapsUS: National Land Cover Database (NLCD; MRLC, 2015)

• Derived from 30m Landsat imagery

• Snapshots: 1992, 2001, 2011

Mexico: Insitituto Nacional de Estadistíca y Geografía

(INEGI, 2015)

• Derived from 30m Landsat imagery

• Snapshots: 1993, 2002, 2011

This material is based on work supported by the National Science Foundation under Grant 1216037 of the Science, Engineering and Education for Sustainability (SEES) program; and Grant SES-0951366, Decision Center for a Desert City II: Urban Climate Adaptation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

1. Bohn, T. J., and E. R. Vivoni, 2016: Process-based characterization of evapotranspiration sources over the North American Monsoon region, Water Resour. Res., 52(1), 358-384, doi:

10.1002/2015WR017934.

2. Haddeland, I., D. P. Lettenmaier, and T. Skaugen, 2006: Effects of irrigation on the water and energy balances of the Colorado and Mekong river basins, Journal of Hydrology, 324(1), 210-223.

3. INEGI, 2015: Instituto Nacional de Estadistica y Geografia, https://www.inegi.org.mx, last accessed: Oct 1, 2015.

4. Livneh B., T. J. Bohn, D. W. Pierce, F. Muñoz-Arriola, B. Nijssen, R. Vose, D. R. Cayan, and L. Brekke, 2015: A spatially comprehensive hydrometeorological data set for Mexico, the U.S., and

southern Canada 1950-2013, Nature Scientific Data, 2, 150042, doi: 10.1038/sdata.2015.42.

5. MRLC, 2015: National Land Cover Database, https://www.mrlc.gov, last accessed: Oct 1, 2015.

Figure 1. Western US-Mexico border region: (a) mean annual precipitation, 1980-2013

(Livneh et al., 2015); (b) dominant land cover in 2001/2 (MRLC, 2015; INEGI, 2015).

Abbreviations: CA = California; AZ = Arizona; NM = New Mexico; TX = Texas; BC =

Baja California; BCS = Baja California del Sur; SON = Sonora; CHI = Chihuahua; SIN

= Sinaloa; DGO = Durango.

1994 North American Free Trade Agreement

(NAFTA)• Lifted trade barriers between the US and Mexico

• Allowed market forces to exploit differences in land valuation,

water pricing, and wages between the US and Mexico

• Drove expansion of export-oriented industries in:

• Horticulture (fresh fruits and vegetables)

• Cattle

• Factories (maquiladoras)

Figure 3. Previous (a) and new (b) canopy schemes in VIC model.

Merged NLCD-INEGI maps:

3. Changes in urban area

4. Conversions between anthropogenic and natural covers

Figure 4. Cropland area fractions at 1/16 degree resolution, in 1992/3 (a), 2011 (b), and difference (c). Figure 6. Urban area fractions at 1/16 degree resolution, in 1992/3 (a), 2011 (b), and difference (c).

Figure 7. Changes in areas of natural land covers between 1992/3 and 2011 that were due to

changes in anthropogenic covers. (a) forests; (b) shrublands; (c) grasslands.Major Trends:

• Expansion of pastures in Sonora and W Chihuahua (1)

• Reduction of pastures everywhere else, including the US

• This is due to (a) growth of Mexican cow-calf operations that export calves to US feedlots, (b) availability of suitable

rangeland in Sonora and Chihuahua, (c) proximity to US market, and (d) proximity to alfalfa croplands

Major Trends:

• Major expansion of urban areas in the US, particularly Phoenix and Las Vegas (1) due to retirement (low cost of living)

and employment

• Minor expansion of urban areas in Mexico near the US border, particularly C. Juarez (2), Tijuana (3), Hermosillo (4)

and C. Chihuahua (5); due to establishment of factories (maquiladoras) for export to US

Major Trends:

• Deforestation in the Sierra Madre Occidental mountains of Sonora, Chihuahua, and Sinaloa (1)

• Conversions of shrublands to pasture in Sonora (2), croplands in Chihuahua (3), and urban areas in Arizona (4)

• Conversions of grasslands to croplands and pasture in Chihuahua (5)

Figure 8. Simulated mean annual irrigation water use over the period 1980-2013, using land cover maps from (a)

1992/3 and (b) 2011; (c) difference between (a) and (b).

1

2

3

4

5

1

2

3

45

1

Simulations• 5 Simulations, each using one of the 5 NLCD-INEGI

maps

• Cover period 1980-2013

Figure 5. Pasture area fractions at 1/16 degree resolution, in 1992/3 (a), 2011 (b), and difference (c).

Figure 9. Mexico’s overexploited aquifers

(CONAGUA, 2016)

1

4

3

2

1

4

3

2

• Horticulture and cattle industries are water-intensive

• Expansion of these industries in Mexico occurred

while Mexico accumulated a 1.5 maf water debt to

the US

Name Description

1993 1992/3 merged snapshot

2002 2001/2 merged snapshot

2011 2011 merged snapshot

1993.anth 2002 baseline, with 1993 extents of urban, crop, pasture

2011.anth 2002 baseline, with 2011 extents of urban, crop, pasture