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2009/10 CalWater

Energy, Water and Regional Climate

Overview

The National Oceanic and Atmospheric Administration (NOAA), the
California Air Resources Board (CARB), the Department of Water Resources
(DWR), and the California Energy Commission (CEC) are proposing a joint
field study of atmospheric processes over California and the eastern
Pacific coastal region that will start in the winter of 2009 and will
continue to the end of the summer of 2010. This overall study will
particularly emphasize the interactions between air quality and climate
change issues including the hydrologic cycle. It will constitute one of
a series of comprehensive regional air quality and climate assessments
conducted by NOAA, the continuation of the CEC regional climate change
studies, an expansion of CARB's leadership of California air quality
studies, an continuation of DWR studies coordinated with the NOAA's
Hydrometeorological Testbed (HMT) activity to include aerosol impacts on
flooding and water resources. In addition, many of the Nation's experts
in air quality, hydrology, and climate change research reside in
California; involving them in the field study will enhance the program
and improve the communication of the scientific findings to the State's
decision makers.

The overall study is composed of two highly coordinated research
activities: 1) a winter/spring study on regional climate and water
resources headed by NOAA's HMT, DWR, and CEC; and 2) a spring/summer
study focused on air quality and regional climate headed by NOAA's air
quality group, ARB, and CEC. The first part of the study is known as
CalWater and the second part of the study as CalNex. This document
mainly discusses the CalWater part of the overall study.

This proposed California-NOAA partnership is consistent with NOAA\'s
emerging vision for a national climate services partnership to manage
risks associated with climate through a distributed network of regional
resources working in close collaboration to ensure that highly usable,
actionable, issue- focused information is produced and evaluated.

**Problem Statement**

Over the past decades in the U.S., emissions reductions implemented for
vehicles and point sources have significantly improved air quality in
most metropolitan areas, while accelerating emissions of greenhouse
gases have increased the net radiative forcing of the climate system.
Overall, from 1990 to 2005, total emissions of CO~2~ in the US are
estimated to have increased by 20.3 percent (from 5062 to 6090 Tg per
year) (*EPA*, 2007). Current trends imply a shift of the state of the
atmosphere toward worsening climate change impacts with only modest
improvement in air quality. The challenge for the future is to adopt new
policies that slow the increase in radiative forcing and increase the
current rate of improvement in air quality. These policy decisions must
recognize that some climate change impacts have a strong regional
dependence, and not simply a uniform global impact.

At present, the ways that interactions between air quality
and warming trends will affect California\'s water supplies
is essentially unknown. Some interactions may tend to reduce and some
interactions are likely to aggravate the effects of warming. Two
examples of how increased air pollution may reduce the adverse effects
of warming include the increased scattering of sunlight off of aerosols
which could partially offset the warming and the reduction in rainfall
intensities due to anti-cloud seeding effects may partially ameliorate
flood risks resulting from warmer conditions. On the other hand,
increased air pollution deposited within the snowpack will reduce the
snow albedo hastening snowmelt which will reduce the efficacy of
California's natural snowpack reservoirs. These non-linear interactions
are dependent on the state of the regional climate with some
interactions dominate in a cooler climate and others dominate in a
warmer climate.

 

California has taken the lead in the Nation's effort to address global
climate change and has proposed an ambitious program to control the
emissions of greenhouse gases in the State. Therefore, California is
particularly interested in finding the most effective way to
simultaneously reduce emissions of greenhouse gases, aerosols, other air
pollutants and their precursors while maximizing the benefits for air
quality, water resources, and climate change.

The goal of CalWater and CalNex 2010 are to develop the science needed
to support policy decisions for the State of California on air quality,
energy generation from hydro power units, and water resources in
general.

**CalWater and CalNex Goals and Objectives**

The goal of this research intuitive is to study the important issues at
the nexus of air quality, climate change and water cycle resource
problems, and to provide scientific information regarding the trade-offs
faced by decision makers when addressing these inter-related issues. In
order to achieve these goals, four main objectives have been created.

1)  Improve our ability to inventory the source and extent of greenhouse
    gas, ozone, aerosol precursors, sulfate and atmospheric mercury
    emissions in California.

2)  Determine chemical transformations and climate processes, including
    modeling nighttime chemistry, ozone transport and effects from
    aerosols.

3)  Characterize and model air flow with considerations for oceanic
    boundary conditions, the coastal range, large inland basins,
    physical and chemical processes, important transport corridors and
    long-range transport to California.

4)  Examine the effects of aerosols and climate change impacts on
    precipitation, water resources and flooding. Studies will
    investigate the effects of aerosols, atmospheric rivers, albedo and
    black carbon deposition on hydrologic resource management.

**Background information on Particulate Matter in the Atmosphere**

***Aerosols***

Aerosols not only have significant and complex climate impacts, but they
also constitute particulate matter (PM), an important air pollutant that
has significant human health impacts, degrades visibility, and
contributes to acidic deposition. The scattering of sunlight by aerosols
presently mask as much as 50% of the greenhouse forcing (Ramanathan et
al., 2001). It should be recognized that where aerosol loading is high,
as in many of the populated areas of the globe (Ramanathan et al.,
2007), the regional cooling effects of aerosols can be much greater than
expected from the global averages that are usually discussed.

Aerosols play a complex role in the climate and water cycle. As
discussed above, improving air quality by reducing aerosols will lead to
increases in greenhouse forcing of the atmosphere (except for Black
Carbon which will decrease the forcing). But not improving air quality
will lead to increases in aerosols which could lead to decreases in the
rainfall and snowpack in the Sierra Nevada Mountains. Some preliminary
insights into this problem are provided by a CEC's Public Interest
Energy Research (PIER) Program study suggesting that aerosols are
already affecting precipitation levels and surface temperatures in
California (Jacobson, 2004).

***Black carbon***

Soot particles are emitted by combustion of fossil fuels and wood. Soot
contains an assortment of carbon compounds that both scatter and absorb
solar radiation in the atmosphere. The particles in soot that absorb
solar radiation are referred to as black carbon (BC). BC is an important
source of global warming and a major contributor to the melting of sea
ice and snow. It is removed from the atmosphere mainly through wash-out
in rainfall and snowfall. BC particles are deposited in snow or ice
during snowfall and "darkens" it. The adsorption of the sun's heat by
the darkened snow increases snow and ice melt rates.

Enhanced melting exposes the underlying darker surface (land or sea)
which enhances solar absorption by about 50 percent or more and
contributes to a substantial surface warming. This mechanism has
contributed to the Sierra snow-pack melting earlier and faster, thus
affecting California's fresh water availability (Hadley et. al. 2007).

In California sources of BC include regional emissions from California's
industrial centers and long-range transport of pollution from East Asia
across the Pacific Ocean. A 2007 CEC funded report by Hadley et al.
(2007) has shown that significant quantities of pollution are
transported from Asia and Eurasia to the West Coast every year.

***Rain Cloud Inhibition***

Particulate matter in the atmosphere has also been shown to increase
cloud formation at the expense of reducing surface precipitation.
Pollution aerosols act as cloud condensation nuclei that are
subsequently incorporated into clouds, thereby slowing the coalescence
of raindrops and delaying the conversion of cloud water into
precipitation. The net rain volume losses in the polluted central and
southern California Sierra Nevada are estimated at 4 x 10^9^ cubic
meters of water per year (over 3 million acre feet of water) (Borys et
al., 2003). Such reductions could cause management problems and
water-supply deficits even without other effects due to a changing
climate.

**Previous Work Supported in part by California**

Air quality studies that have been carried out over three decades in
California, and their results provide a firm foundation for defining
outstanding air quality problems that can be directly addressed by
CalWater and CalNex 2010. Previous work by the California Energy
Commission has investigated the amount of BC in the rain and snow of
California. The average BC concentration in coastal rain was 5.7
[+]{.underline} 3.5 ng/g (Hadley et. al. 2007). The average BC
concentration in snow was 5.0 [+]{.underline} 2.3 ng/g at the remote
mountain site and 6.9 [+]{.underline} 3.1 ng/g at the polluted site.
Calculated air mass back trajectories indicate strong regional and local
sources for the aerosol, including BC, in the precipitation and snowfall
of California.

Several field studies, conducted within the last decade have shown that
Trans-Pacific transport of pollution, including BC, from Asia to North
America can be significant, especially in the late winter and early
spring (Hadley et al. 2007). Not only does the timing of this enhanced
transport occur at the same time as the onset of spring melt, it also
impacts high-elevation sites with greater significance (Hadley et al.
2007).

A recent long-range aircraft experiment using the NCAR-GULF V (Stith and
Ramanathan 2007) tracked soot-dust plumes from western Pacific to North
America. They found that the BC observed in California precipitation is
likely a combination of both local and transported sources, especially
in March and early April. Their modeling studies have predicted that
snow surface albedo has reduced by approximately 0.3 percent, snow depth
by about 0.5 percent, and increased ground temperatures over land by
about 0.198°F due to BC in California precipitation.

A 2005 study funded by the California Energy Commission with Dr. Daniel
Rosenfeld and Dr. William Woodley, along with their research team, found
that atmospheric aerosols can impede rain and snow formation in the
Sierra Nevada Mountains (Woodley Weather Consultants, 2005; Rosenfeld et
al. 2008). This effect is exhibited in different ways in clouds --
either strengthening deep convective clouds or suppressing the amount of
surface precipitation from shallow clouds over mountains. These studies
estimate that California's annual mountain precipitation has decreased
by 10 to 25 percent due to pollution aerosols emitted from urban and
industrial areas.

A more recent study by the Woodley Weather Consultants (2007) showed
that increased aerosol pollution from urban areas over the last 50 years
has reduced rain and snow formation in the central and southern Sierra
Nevada Mountains. This decreasing water runoff directly impacts in-state
hydroelectric generation and that California's water supplies,
especially for agriculture, could be jeopardized. The net rain-volume
losses in the polluted central and southern California Sierra Nevada are
estimated at 4 x 10^9^ cubic meters (over 3 million acre feet) of water
per year.

**Previous NOAA-led Work on Precipitation and Water Resources in
California**

NOAA has conducted a number of major field studies in California since
1997 (CALJET, PACJET, HMT) focused on understanding key precipitation
process from both weather and climate perspectives, exploring how better
to predict the major storms and developing techniques to monitor key
atmospheric conditions. This work has resulted in the following key
developments and findings relevant to CalWater.

Observations using new radar and in situ techniques have documented a
shallow, but efficient precipitation process (referred to as
"non-bright-band rain'). It is important because it produces typically
30% of the total seasonal rainfall, is capable of producing heavy enough
rainfall to cause flooding, and yet is not monitored by traditional
radar or satellite methods and is not well represented in numerical
models (White et al. 2003, Neiman et al. 2005). It is characterized by
very small drop sizes with small fall velocities, and occurs in both the
Coast Ranges and Sierra Nevada. Distinguishing anthropogenic aerosol
impacts on precipitation must control for this natural phenomenon.

Atmospheric rivers (AR), first explored via numerical model diagnostics
in the 1990s, have now been documented both offshore and along the coast
using data from NOAA P-3 research aircraft, satellites and wind
profiling radars. AR's are narrow regions of strong horizontal water
vapor transport located mostly in the lowest 2 km of the atmosphere.
They typically contribute to major snowfall events that build snowpack
(Neiman et al. 2008) and the strongest and slowest moving ARs cause
flooding (Ralph et al. 2006). The role of ARs in transporting aerosols
across the Pacific and from the coast to the Sierras, where the AR
conditions are responsible for major rain and snow events, remains to be
explored.

These studies have also helped develop and test new observing
techniques, including those that use ground-based remote sensors (S-band
vertically profiling precipitation radars -- see White et al. 2003; wind
profiling radars -- see Ralph et al. 2006; polarimetric scanning radar),
in situ sensors to measure drop size distributions in rain and snow
(disdrometers), an integrated approach to monitoring AR conditions at
the coast (see Ralph et al. 2006), and aircraft-based sampling
strategies to monitor ARs offshore with manned or unmanned aircraft.

Planning and Integration of Research Programs for CalWater and CalNex
2010

The major research efforts are planned for 2009/2010 but some work will
take place during summer 2008 and winter 2009. The season and length of
time of the major platform deployments has not yet been determined. It
may be possible to deploy the two NOAA aircraft during two shorter
deployments (3 to 4 weeks) in different seasons (for example, early
spring and summer), or a single longer deployment (approximately 6
weeks). The NOAA ship will be available for only a single deployment,
which has tentatively been scheduled for spring, but it may be possible
to modify that schedule if the scientific objectives dictate. Most of
the CEC efforts will be focused in the winter and spring seasons and
will be designed to address the effect of aerosols on the hydrologic
cycle and regional climate.

Planning decisions for CalWater and CalNex 2010 measurements will be
informed by interim studies funded by CARB, NOAA, and CEC:

-   During the summer of 2008 the NASA DC8 will characterize atmospheric
    composition through in situ measurements, and the NASA P3 will
    examine vertical profiles of radiative fluxes and in situ aerosol
    properties. ARB is funding this study.

-   A key opportunity for leveraging on water-resources applications is
    the collaboration with the NOAA Hydrometeorological Testbed (HMT)
    and Coastal Weather and Air Quality programs that have been
    collecting observations in California since 1997. DWR and NOAA are
    working on this interim study.

-   The CEC has contracted with the Scripps Institution of Oceanography
    to use unmanned aircraft to determine the concentration of black
    carbon aloft during different parts of the year in 2008, and will
    also conduct preliminary measurements to determine how black carbon
    and aerosols are affecting the atmospheric energy budget. Scripps
    will also continue to measure the amount of black carbon deposited
    to the snow pack in the Sierra Nevada to estimate its effect on snow
    albedo.

-   Prof. Steve Cliff from U.C. Davis will continue measuring particles
    at different size bins and determining the chemical composition of
    these particles. These measurements are being taken in medium to
    high elevation sites in the Sierra Nevada.

Research Platforms and Instrumentation

*Measurements Via Aircraft*

#  One of NOAA's four-engine Lockheed WP-3D Orions will take measurements of a wide variety of pollutants, particulate matter and greenhouse gases, with 100 m spatial resolution. The WP-3D is able to follow the transport and transformation of emissions throughout California and surrounding regions. A differential absorption lidar (DIAL) will be deployed on a NOAA Twin Otter aircraft for remote sensing of local and regional ozone and aerosol distributions. This instrument is designed to characterize the three-dimensional structure of pollution plumes from urban areas and point sources. The instrument can also identify and isolate regions and layers of high ozone concentration, observations of atmospheric layering as characterized by aerosol and ozone structure, and investigate local meteorological effects such as sea breezes, urban heat islands and orographic effects on pollution transport and mixing. 

#  

A CEC-sponsored project with Scripps would deploy light-weight unmanned
Aircraft Systems (UASs) in California to routinely monitor vertical
profiles of black carbon, ozone, aerosol concentrations and solar fluxes
(to estimate aerosol forcing). In addition, Scripps will collaborate
with NOAA to deploy the UASs from ships to conduct detailed vertical
structure measurements of water vapor, aerosol concentrations, cloud
condensation nuclei and cloud drop concentrations in atmospheric rivers
offshore. The CEC may also be able to bring a cloud-physics aircraft for
in-situ measurements of aerosols and cloud properties.

***Ship based Measurements***

An instrumented ship is an ideal platform to study the meteorological
and chemical processes occurring within port areas (e.g. Long Beach, San
Francisco Bay) and along the coast of California. The NOAA *R/V* *Ronald
H. Brown* can be used to investigate air masses as they move offshore or
onshore and study the chemical transformations in the polluted marine
boundary layer. The instrumentation available for the ship includes in
situ measurements comparable to those on the WP-3D aircraft plus remote
sensing instruments including ozone/aerosol lidar, radar wind profiler,
Doppler lidar, C-band radar and radiosondes.

***Ground-Based Measurements***

California experiences a heterogeneous and complex diurnal cycle of
meteorology caused by its proximity to the Pacific Coast, large urban
areas and a variety of heterogeneous land-surface types that produce
local circulations. Therefore, three types of ground-based measurements
will be made. First, upper-air observations will be made to characterize
California's meteorological processes controlling the transport of
atmospheric pollutants. NOAA and partners in CalNex 2010 will deploy a
network of integrated boundary layer observing systems. These
instruments provide continuous profiles of wind speed and wind direction
in the boundary layer and lower free troposphere and derived mixing
heights. Each profiler will also include a radio acoustic sounding
system (RASS) for temperature profiling.

Second, Ground-based chemical measurements will include both in situ and
remote instrumentation comparable to the WP-3D and *Ronald H. Brown*
instrument packages plus instrumentation that cannot be deployed on
either platform. A transect of sites from the coast to the central
valley will count the number and size of raindrops along with their
chemical and isotope concentration. This operation will provide valuable
information on the life history of the surface precipitation.

Third, a ground-based precipitation measurement system will be deployed
that will include precipitation radar and in situ capabilities in the
region of the Sierras that is often downwind of San Francisco. Adding in
situ and ground-based aerosol measurement capabilities to selected NOAA
Hydrometeorological Testbed (HMT) field sites which already have
precipitation radars and other meteorological instruments in the
American River Basin would enable studies like that of Borys et al.
(2003) on the impact of aerosols on precipitation efficiency, including
the impact on riming. In addition, the coastal area north of San
Francisco could be instrumented with in situ aerosol sensors at NOAA HMT
field sites to provide a comparison in a relatively pristine
environment. Each of these is already heavily instrumented as
*atmospheric river observatories* intended to make long-term
measurements to monitor changes in atmospheric rivers that may develop
in a changing climate. Finally, efforts to measure integrated water
vapor using GPS sensors at the surface should be considered to extend
the satellite-based measurements from SSM/I available offshore.

***Satellite Observations***

Retrievals of aerosol and trace gas information from current research
and operational satellites have great potential to assist in several of
the science objectives. Instruments on NASA and NOAA satellites are able
to observe pollutants, aerosol transport, the distribution of droplet
sizes in clouds and integrated water vapor contents over the oceans.
Polar-orbiting satellites (e.g., MODIS) provide coverage once a day
globally, while geostationary satellites (e.g., GOES) provide coverage
over the continental United States once every fifteen minutes. It will
be very important to integrate the satellite instrumentation community
into the planning process. Integrating *in situ* and satellite data with
modeling will be essential to address the science objectives.

Organization of a Detail Science Plan

DWR, NOAA, and CEC will prepare a detailed science plan with assistance
from the following scientists: Prof. Ramanathan (Scripps), Dr. Dan Cayan
(Scripps), Dr. Michael Dettinger (Scripps), Prof. Rosenfeld (Hebrew
University), Prof. Mark Jacobson (Sanford), Dr. R. Borys (DRI), Dr.
Christopher Williams (CIRES), Dr. David Kingsmill (CIRES), Dr. George
Kiladis (NOAA/ESRL), Paul Neiman (NOAA/ESRL), and Dr. F. Martin Ralph
(NOAA/ESRL). The three agencies plan to organize a workshop in San Diego
in the summer of 2008 to start developing a detailed science plan that
includes scientific hypotheses and critical elements of an
implementation strategy. Four subjects that will be addressed at this
workshop include:

1)  Long-range transport and deposition of black carbon in snow and its
    impacts on snowpack.

2)  Reducing uncertainties in the impacts of anthropogenic aerosols on
    precipitation.

3)  The role of shallow (non-bright-band) rain processes in modulating
    aerosol impacts on precipitation and the deposition of black carbon.

4)  Understanding the role of atmospheric rivers on black carbon
    transport, aerosol entrainment and precipitation formation, for both
    water supply and extreme events.

Science Synthesis and Assessment: Providing Timely and Relevant
Information for Policy Makers

NOAA, ARB, DWR, and CEC will provide Fact Sheets and Synthesis Reports
that provide the most relevant results of the field studies involved
with CalNex 2010. Informal presentations and conferences will also be
organized to transfer scientific results to a lay audience.

**Projected Major Milestones**

Major milestones for this project include:

August/Sept 2008: CalWater Science Plan meeting (at Scripps)

October 2008: Joint CEC-NOAA Science Plan completed

November 2008: Begin "Early Start" Data collection Period (through
Spring 2009)

January 2009: NOAA and CEC overall resource levels defined

July 2009: Specific CEC and NOAA projects approved

Includes final Experimental Design and Implementation Plan

November 2009: Start CalWater 2009/10 Field Campaign

Spring 2010: End CalWater 2009/10 Field Campaign

Fall 2010: CalWater Field Campaign Data Workshop

Summer 2011: CalWater Summit: Lessons Learned and Recommendations

**References**

Borys, R. D., D. H. Lowenthal, S. A. Cohn, and W. O. J. Brown, 2003:
Mountaintop and radar measurments of anthropogenic aerosol effects on
snow growth and snowfall rate. Geoph. Res. Lett., 30, doi:
10.1029/2002GL016855.

EPA (2007), Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990
-- 2005, EPA-430-R-07-002, U.S. Environmental Protection Agency,
Washington D.C

Hadley, Odelle L, C. Corrigan and V Ramanathan, 2007.Measurements of
Black Carbon in Snow and Rain in the Sierra Nevada Mountains and on the
California Coast. California Energy Commission, PIER Energy-Related
Environmental Research.

Jacobson, M. (2004), Effects of Anthropogenic Aerosol Particles and
Their Precursor Gases On California and South Coast Climate.
CEC-500-2005-003 California Energy Commission, Sacramento, CA.

Neiman, P. J., B. E. Martner, A. B. White, G. A. Wick, F. M. Ralph, and
D. E. Kingsmill, 2005: Wintertime nonbrightband rain in California and
Oregon during CALJET and PACJET: Geographic, interannual, and synoptic
variability. Mon. Wea. Rev., 133, 1199-1223, doi:10.1175/MWR2919.1.

Neiman, P. J., F. M. Ralph, G. A. Wick, J. D. Lundquist and M. D.
Dettinger, 2008: Meteorological characteristics and overland
precipitation impacts of atmospheric rivers affecting the West Coast of
North America based on eight years of SSM/I satellite observations. *J.
Hydrometeor.*, **9**, 22-47.

Ralph, F. M., P. J. Neiman, G. A. Wick, S. I. Gutman, M. D. Dettinger,
C. R. Cayan, and A. B. White 2006: Flooding on California's Russian
River: The Role of Atmospheric Rivers. Geophys. Res. Lett., 33, L13801,
doi:10.1029/2006GL026689.

Ramanathan, V., F. Li, M.V. Ramana, P.S. Praveen, D. Kim, C.E. Corrigan,
H. Nguyen (2007). Atmospheric Brown Clouds: Hemispherical and regional
variations in long range transport, absorption, and radiative forcing,
*J. Geophys. Res.*, 112, D22S21, doi:10.1029/2006JD008124.

Ramanathan, V., P. J. Crutzen, J. T. Kiehl and D. Rosenfeld, 2001:
[Aerosols, Climate, and The Hydrological
Cycle](http://www.sciencemag.org/cgi/reprint/294/5549/2119.pdf).
Science, 294, 2119-2124.

Stith, J., and V. Ramanathan (2007), The Pacific Dust Experiment
(PaCDEX) Field Campaign: A summary of accomplishments during the field
campaign and examples of early results, paper presented at American
Geophysics Union Fall Meeting, San Francisco.

White, A. B., P. J. Neiman, F. M. Ralph, D. E. Kingsmill, and P. O. G.
Persson, 2003: Coastal orographic rainfall processes observed by radar
during the California Land-Falling Jets experiment. *J. Hydrometeor.*
**4**, pp. 264-282.

Woodley Weather Consultants. 2005. The Use of a Cloud Physics Aircraft
for the Mapping of Pollution Aerosols Detrimental to Winter Orographic
Precipitation over the California Sierra Nevada. California Energy
Commission, PIER Energy-Related Environmental Research.
CEC-500-2005-205.

Woodley Weather Consultants. 2007. Physical/Statistical and Modeling
Documentation of the Effects of Urban and Industrial Air Pollution in
California on Precipitation and Stream Flows. California Energy
Commission, PIER Energy‐Related Environmental Research Program.
CEC‐500‐2007‐019.

Rosenfeld, D., W. L. Woodley, D. Axisa, E. Freud, J. G. Hudson, and A.
Givati (2008), Aircraft measurements of the impacts of pollution
aerosols on clouds and precipitation over the Sierra Nevada, J. Geophys.
Res., doi:10.1029/2007JD009544, in press.