Climate changing from rain to snow with some measurable flooding impacts

We had flood warnings over the weekend that didn't amount to much, fortunately. Yesterday the weather cleared enough to show the Mount Hamilton Range covered in snow, which helps a great deal. The higher-altitude precipitation comes down as snow instead of rain during storm events and melts slowly over a period of days, instead of surging down in a few hours with all the other rain.

That's how it's happened in the past and today, but will be less true in the future due to climate change. While more intense storms and flooding are a possible consequence of warming due to changed weather patterns, that effect is hard to quantify. Changing from snow to rain, however, isn't so hard to make some rough calculations.

The saturated adiabatic lapse rate is just under 5 degrees Celsius per 1000 meters. The standard prediction from the latest International Panel on Climate Change for warming in the next few decades is .2 degrees Celsius per decade. Putting the two figures together means that after ten years, the snow line in a typical storm would be 40 meters higher than today, or 80 meters higher after 20 years (about 130 and 260 feet, respectively). While that may not sound like a lot, it could potentially turn a great deal of snowfall into rain, and it's only going to get worse.

While this is far from the most serious climate change impact, it's fairly quantifiable. The question is whether land use agencies will take this under consideration in their new responsibilities to prepare for flooding.

-Brian

UPDATE: See page 2 to see a graph of California temperatures. It's in Fahrenheit, but looks like roughly .5 degrees/decade, or about the same as the IPCC global prediction in Celsius.

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Meeting notes on AB162 - new requirements for General Plans to address flooding

(Another in my occasional series of notes from meetings, this one a briefing by the Water District to other agencies regarding new requirements under California law AB162 to address flooding issues in General Plan revisions. Hopefully it translates beyond just being notes to myself. -Brian)

AB162 Meeting Notes Feb 18 at Water District

Mandatory for housing revision after 1/1/09

Also requires flood analysis in land use, housing, conservation, and safety

Requires local govts to collaborate plan for and reduce flood risks

Requires update frequency, content analyses for flood and data required

Q for audience when planning GP updates?

Mtn View expects complete by end 2010

Water Board proposing new beneficial use - flood storage

County just working on housing

San jose – almost done with housing, comp update end by 2011

Palo Alto – amending GP just cleanup, draft hsg by june 30

Cupertino – updating housing, haven't begun GP update

Santa Clara city – GP update in 2010

Campbell Sunnyvale, LA Hills – working on hsg

General hierarchy of 162

Rv FEMA maps, DWR maps, any relevant COE maps/data

162 says updates of hsg triggers updates of two other elements (my note – if this is true, major probs ahead)

Water Dist draft Comp Plan URL: state-scvwdcp.migcom.com

Land use element

162 req annual rv of areas subject to mapping from FEMA and DWR – NEW

Must i.d. flood risk areas – overlay

Specified data from FEMA or DWR

Msc.fema.gov

Releasing gis online in may

Other data also useful – such as historic flooding data from Wat Dist – flood damages reports dating back to 1967 with maps

Online at Valleywater.org – flood protection – flooding in valley – historic flood reports

My notes – this is good – cannot ignore historic flooding data

Opportunity to consider how imperv surface lead to increased flooding among other impacts

Conservation element – upon next revision of hsg element, the conservation element – i.d. streams, flood corridors, rip habitats, and land that may accommomodate flloddwater for purposes of groundwater recharge and stormwater mgmt.

My note – recharge, not just stormwater

Where do you get data

Gis based stream maps

Recharge maps

Project specific info

Valleywater.org – quicklinks – gis – looks like needs arcview software

Useful piece of info – wetlandtracker.org

Safety element – reviewed every time housing element reviewed

Min risks of llod to new development; evaluate whether ne dev should be located flood zones; maintain pub services during flooding; locate essential facilities outside flood hazard; establish coop among pub agencies resp for flood protection

A flood ordinance can replace or be the relevant part of safety element if meets same requirements

Opportunities – policies that reduce runoff and increase absorption

Housing - consider level of protection provided by flood mgmt infrastructure

City of Richmond incorporating a climate change element into their GP

Feb 26^th joint venture climate change and transprortclimate action plan for san jose

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The highway lobby can be beaten

Jonathan Zasloff writes of the difficulty that environmental advocates have had in fighting the highway lobby, pointing to SB375, a California climate change law, that was nearly defeated solely by the highway lobbyists. Still, SB375 became law, and our earliest victories here at CGF were in fighting plans to strew massive highways all over the Peninsula.

Lots to be done, but we'll be working hard to do it.

Bonus blogging - new information's out showing the earthquake hazard of building in floodplains of major streams: "If a major earthquake rattles the South Bay, the sandy soils alongside San Jose's two largest rivers pose the highest risks to modern businesses and homes in Santa Clara County, according to new seismic maps by the U.S. Geological Survey. The maps reveal the hidden danger along San Jose's ancestral Guadalupe River and Coyote Creek flood plains...."

Still more reasons to keep those floodplains natural and open, whenever possible.

-Brian

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