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Weather & Climate

CLIMATE is what you ______ WEATHER is what you ___– R.A. Heinlein

How do we determine climate?

• Temperature• Precipitation• Wind, Humidity, ….• …… over many years• Hydrologists focus on streamflow!

• Most important features: – Variability & Predictability

Tucson Climate Pattern

http://www.wrcc.dri.edu/summary/climsmaz.html3

Winter:• Large scale, homogenous storms from thePacific Ocean

• Important for water supply and snow

Summer:• Complex convective storms from the Gulf of Mexico

• Small scale, heterogeneous, intense and short-lived storms

• High evaporation

Regional Seasonal Climatic Patterns% Precipitation in Winter (Oct-Mar)

% Precipitation in Summer (July & Aug)

Annual variability of temp/precip

http://www.wrh.noaa.gov/twc/climate/seazDM.php5

www.wrh.noaa.gov/climate/temp_graphs.php?wfo=twc

http://www.wrcc.dri.edu/pcpn/westus_precip.gif

Remember-What factors control precipitation in the SW?

2010 -- SWE Variability -- 2006

Hydrologic events affected by climatic fluctuations

Timing of snowmelt runoff

Quantity of baseflow

Occurrence of floods

Duration and extent of drought10

MAJOR SOURCES OF VARIABILITY

Can we predict next year’s water supply?

What are El Niño & La Niña events?

• Changes(+/-) in normal sea surface temp. (>0.5°C)

Eastern Pacific:• El Niño: increase (+), warmer water temperature• La Niña: decrease (-), cooler water temperature

“Watch Areas”

Pacific sea surface temperatures along the equator tend to oscillate between warm and cold along the equator every three to seven years.

This oscillation is called the El Nino-Southern Oscillation (ENSO).

El Niño episodes (also called Pacific warm episodes or ENSO) and La Niña episodes (also called Pacific cold episodes) represent opposite extremes of the ENSO cycle.

Nice ENSO educational resources: http://www.srh.noaa.gov/srh/jetstream/tropics/enso.htm

http://www.srh.noaa.gov/srh/jetstream/tropics/enso_patterns.htm

El Nino – Weak Walker Circ. La Nina – Strong Walker Circ.

coolerwarmer

http://www.esrl.noaa.gov/psd/people/klaus.wolter/MEI/#LaNina

http://www.worldatlas.com/webimage/countrys/islands/pacifics/tahiti.gif

http://www.hplgroup.com/img/map_darwin.gif

www.asturi.com/pages/ galleries.html/tahiti_moorea_map.gif

The Southern Oscillation Index (SOI) is one measure of the large-scale fluctuations in air pressure occurring between the western and eastern tropical Pacific (i.e., the state of the Southern Oscillation) during El Niño and La Niña episodes.

Traditionally, this index has been calculated based on the differences in air pressure anomaly between Tahiti and Darwin, Australia.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensocycle/soi.htmlArizona Water Issues 16

THE SOUTHERN OSCILLATION INDEX (SOI)

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensocycle/soi.shtml

The Southern Oscillation Index (SOI) is one measure of the large-scale fluctuations in air pressure occurring between the western and eastern tropical Pacific (i.e., the state of the Southern Oscillation) during El Niño and La Niña episodes.

ENSO cycle has an average period of about four years, although in the historical record the period has varied between two and seven years.

El Niño

17www.cpc.ncep.noaa.gov/data/indices/

The "Pacific Decadal Oscillation" (PDO) is a long-lived El Niño-like pattern of Pacific climate variability. Causes for the PDO are not currently known.Two main characteristics distinguish PDO from ENSO: First, 20th century PDO "events" persisted for 20-to-30 years, while typical ENSO events persisted for 6 to 18 months; Second, the climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics -the opposite is true for ENSO.

warm phase cool phase

Arizona Water Issues 18

Pacific Decadal Oscillations

jisao.washington.edu/pdo

ENSO Forecast - Current

ENSO Forecast

Relative Performance

http://iri.columbia.edu/climate/ENSO/currentinfo/SST_table.html

Current conditions – Another strong El Nino?

http://earthobservatory.nasa.gov/IOTD

Can you interpret this?

iri.columbia.edu/climate/ENSO/currentinfo/QuickLook.html

CPC Ocean Temp. Forecast

www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/

El Niño = Wet in Southwest US

La Niña = Dry in Southwest US

Warm winter storms are more common during El Nino

Below average flows in the CR are more common during La Nina

“Tele – connections”

Teleconnections

REGIONAL EVIDENCE OF TELECONNECTIONS

Dry period with weak El Ninoand strong La Nina events

Strong El Nino events thatproduced wet winters andhigh flow in Arizona

Effect of ENSO on Winter Precip. in AZ

All EL NINO Years (1935-97)

Gila River @ Calva Daily Winter Streamflow (cfs)

All LA NINA Years (1935-97)

Climate variability: spatial, interannual, regimes (decadal), climate change

Credit: Tom Pagano

Annual State of the Climate1895-2009

http://www.ncdc.noaa.gov/oa/climate/research/2008/ann/ann08.html

How important is predictability?

Impacts of Climatic Variability - NW

http://cses.washington.edu/cig/pnwc/clvariability.shtml

How important is predictability?

Whisker plots

PALEO RECORDS

Climate Variability

Global warming or Global change?37

How do we determine climate for time before we took measurements?

• Tree-ring records• How do these work?• Tree ring width based on:

– soil and air temperatures – soil moisture conditions– sunshine– wind

• The factors change based on climate

Tree-ring and streamflow correlation

Annual Average Flow for the Gila River below Coolidge Dam

1000150020002500

1900 1920 1940 1960 1980 2000

•Tree-rings correlate to certain climate events

•Especially El Niño & La Niña events

•Tree-rings have a longer period of record than most streamflow & precipitation data sets

1500___1600___1700___1800___1900___2000

????????????????????????????1900___2000

CR at Lee’s Ferry

Adjusted for:• Water year vs. calendar year• 0.29 Maf bias in dam inflows• Glen Canyon Dam Construction• Consumptive users were kept in

Observed/Estimated CR flow data

Meko, LTRR, Presentation to CDWR, 6/04http://pubs.usgs.gov/fs/2004/3062/41

Tree ring dendro-hydrology:Fact: We are in a historic drought

Note 1920’s flow was historic high

Eos, Vol. 89, No. 9, 26 February 2008MacDonald, UCLA

“Taken together, climatological and paleo-climatological evidence does not provideany reason to conclude that events such asthe early 21st-century drought could notpersist longer than the 5- to 8-year durationof historical droughts of the twentieth century.Prolonged episodes of aridity persistingfor a decade or more are apparent in manypaleohydrological records, and conditionsin the Pacific appear to have played a keyrole in these episodes.”

Variability at 2 scales; Reconstructed flow

Things to think about• How to illustrate project city climate and what

factors affect it?• How does precipitation vary in time and

space?– What areas get the most precipitation and why?– Why are summer storms different from winter

storms?– What causes extreme events? Are they

predictable?• How does uncertainty in precipitation affect

water resources?• What climate factors are of critical

importance to Arizona and the southwest?46

How will climate change affect AZ?

From: Climate Change and Natural Resources in Pima County, 2010

Hotter & Drier

Declining Sierra Snowpack

ftp://

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