CZOs & water security: Western U.S. lessons &

global implications

NASA-MODIS satellite image

Roger BalesProfessor & Director

Sierra Nevada Research Institute

UC Merced

Making a water-secure world – the three I’s

Better & more-accessible

INFORMATION

INFRASTRUCTURE to store, transport

& treat water

Stronger & more-adaptable

INSTITUTIONSHARD SOFT

Making a water-secure world – the three I’s

Better & more-accessible

INFORMATION

INFRASTRUCTURE to store, transport

& treat water

Stronger & more-adaptable

INSTITUTIONS

Water security: the reliable availability of an acceptable quantity & quality of water for health, livelihoods & production, coupled w/ an acceptable level of water-related risks

Ecosystem services

Making a water-secure world – the three I’s

Better & more-accessible

INFORMATION

INFRASTRUCTURE to store, transport

& treat water

Stronger & more-adaptable

INSTITUTIONS

Ecosystem services

Making a water-secure world – the three I’s

Better & more-accessible

INFORMATION

INFRASTRUCTURE to store, transport

& treat water

Stronger & more-adaptable

INSTITUTIONS

Water is fundamental to sustainable ecosystem services. Water management therefore translates into managing ecosystem services, and must be a fundamental goal of virtually all such efforts.

Much of the water supply for the semi-arid Western U.S. derives from mountain snowpacks

Warming by +2 to +6oC drives significant changes:

– rain-vs-snow storms *– snowpack amounts *– snowmelt timing *– flood risk– streamflow timing *– low baseflows– growing seasons *– recharge?– drier soil in summer

Precipitation changes?

Already observed (*)

Water security lies at the heart of adaptation to climate change

Includes both:̶8 ‘hard’ options to capture & control water̶8 ‘soft’ tools to manage demand as well as

increase supply, e.g. water allocation, conservation, efficiency & land-use planning

What California is doing:̶+ Planning for infrastructure̶+ Collaboration & integration in planning,

management̶+ More information-intensive decision support

General feeling in the water community that soft opportunities will be insufficient

Southern Sierra CZO is addressing knowledge gaps in all 3 areas

Critical zone observations are a foundation for water security

CZO

UCM

CZO location

Southern Sierra CZO is located at elevations 1750-2100 m, across the rain-snow transition, in a very productive mixed-conifer forest, with extended measurement nodes at elevations 400-2700 m

lidar

A new generation of integrated measurements

eddy correlation

satellite snowcover

embedded sensor

networks

isotopes & ions

sap flow

low-cost sensors

sediment

Southern Sierra CZO

CZO

N-S transect of research catchments

MODIS image

Main CZO site

6001200180024003000

Elev., m

San Joaquin Experimental

Range400 m

Shorthair Creek

2700 mCZO P301

2000 m

Soaproot Saddle1100 m

E-W transect of flux towers

NEON to follow same E-W transect as CZO

Increase in water yield w/

elevation

Decreasing temperatureIncreasing snow fractionDecreasing LAICoarser soils

Implication for 2oC warmer climate:Reduce runoff by 10-40% in mixed conifer forest

0.1 increase per 350 m

95018001950

750

Year Precip, mm

Wet years

Dry years

3oC

X

X

X Water-balance Et (2009-10)

Elevation, m

ET fl

ux, m

m y

r-1Evapotranspiration (ET) across an elevation transect

– Lower elevation is water limited– Higher elevation is cold limited– Highest current ET in rain to rain-snow-transition region of

mixed conifer forest – year-round growth

Is ET really this high?

Modeled ET in Yosemite (Lutz et al., 2010) – Ecological & climate models often have ET values in the 200-500 mm range

– Deficit based in part on 1-m or 2-m soil depth

– CZO results suggest values in the 500-1200 mm per year range –deeper active storage of water

Precip = ET + Streamflow

0

50

100

150

200

250

300

350

400

015

030

045

060

075

090

010

5012

0013

5015

0016

5018

0019

5021

0022

5024

0025

5027

00

Num

ber o

f day

s

Elevation (m)

Days water limited

Days freeze limited

Growing season

0

50

100

150

200

250

300

350

400

400 1160 2060 2700

Num

ber o

f day

s

Elevation (m)

Days water limited

Days freeze limited

Growing season

water limit

cold limit

growing season

100

0

200

300

Days

100

0

200

300

Days

300 900 1500 2100 2700Elevation, m

water limitcold

growing season

Conventional wisdom: short growing seasons, small changes w/ elevation

Observations: – Water & cold limitation thresholds

that kick in at lower/higher elevations

– Sweet spot at mid elevation – only weak water/cold co-limitation

Implications– Warming alone could cause big

change in growing season length– Ecohydrologic & biogeochemical

processes may not be buffered against warming

Water & temperature limits

Some implications of steep elevation gradients in ET & runoff for water resources

Forest management is important for water yield & the timing of snowmelt runoff

Downstream beneficiaries have a stake in upstream watershed management

Better measurement & process understanding are critical to realizing benefits of management actions

SS-CZO is addressing knowledge gaps & stimulating adaptive management

Developing a new water-information system for California & beyond – American R. basin prototype

Strategically place low-cost sensors to get spatial estimates of snowcover, soil moisture & other water-balance componentsNetwork & integrate these sensors, w/

satellite data & modeling, into a single spatial instrument for water-cycle estimates in progress

Scaling CZO results for water, flood & drought management

Southern Sierra CZO is a multi-campus program & a community resource

R. Bales, P. KirchnerM. Conklin, R. LucasS. Hart, J. BlankenshipA. Behre, E. Stacy

M. Goulden, A. Kelly

C. Tague, K. Son

J. Hopmans, P. HartsoughB. Houlton, S. EndersT. O’Geen

D. Johnson, C. Woodward

C. Riebe, B. Jessup

S. Glaser, B. Kerkz

C. Hunsaker

N. Molotch, K. Musselman