Overview of the Water and Energy Cycle

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Overview of the Water and Energy Cycle
Paul R. Houser

• Outline
• Define water and energy cycle
• Why water energy cycle is important
• Outstanding water energy cycle issues
• NASAs role in water energy cycle research
• The need for an integrated research program

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Earth Science Enterprise
Earth Science Enterprise
National Aeronautics and Space Administration


Water and Energy Cycle Focus Area
The global water and energy cycle encompasses the
movements, transformations, and reservoirs of
water, energy, and water-borne materials
throughout the Earth system and their
interactions with ecosystems and the global water
system. The global water and energy cycle
operates on the full continuum of space and time
scales and involves phase changes and energy
exchanges.
Paul R. Houser, NASA/GSFC Hydrological
Sciences Paul.R.Houser_at_nasa.gov
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The Water and Energy Cycle
Water in the climate system functions on all time
scales From hours to centuries

• The Earths climate is primarily driven by solar
  forcing and terrestrial radiation processes
• The key feedbacks effecting climate sensitivity
  are water vapor and cloud-radiation processes
• Terrestrial hydrologic processes drives climate
• Changes in precipitation patterns and
  intensity, represents the most serious
  manifestation of climate variability and change

The Energy and Water Cycles are tightly
intertwined Solar radiation drives and
feedbacks with the water cycle, and energy is
transferred through water movement and phase
change.
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Seamless Suite of Forecasts to meet WE cycle
needs
Boundary Conditions
Initial Conditions
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Do we need better water energy cycle
prediction?
The Grim Arithmetic of Water---Official
Discussing Emerging Freshwater Crisis---Source
September 2002 National Geographic
Water and energy research is required for better
prediction of freshwater resources, climate
change , weather, and the precipitation because
it is the key process that links them all.
Population is dramatically increasing Ultimately,
a limited water supply will meet limited needs
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Why study the water and energy cycle?...
Variations in greenhouse gases, aerosols, and
solar activity force changes in climate
but, consequences of climate change are realized
through the water cycle.
and climate warming is regulated through
water-energy feedbacks.
is the cycling, distribution, or extremes of the
global water and energy system changing?
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The Water-Energy-Climate Feedback

• Increasing Temperature -gt increased atmospheric
  moisture -gt increased Precipitation
• Hence increased risk of hydrologic extremes

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Climate Predictions of Water Energy Cycle Trends
source Ziegler et al, J. Clim, 2003
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A generally accepted hypothesis regarding
acceleration of the global water cycle

• According to model predictions, the most
  significant manifestation of climate change would
  be an acceleration of the global water cycle,
  leading to a general exacerbation of extreme
  hydrologic regimes, floods and droughts (NASA
  Global Water and Energy Cycle solicitation,
  2000).
• There is evidence that suggests that the global
  hydrologic cycle may be intensifying, leading to
  an increase in the frequency of extremes
  (Hornberger et al, USGCRP water cycle science
  plan)
• Climate models generally project an acceleration
  in the rate of global water cycling and an
  increase in global precipitation (Morel, GEWEX
  News, 2001)

Observations over the last century indicate

• Increased in mean and extreme P over much of
  continental U.S. except winter
• Apparent changes in floods.

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Precipitation Trends
Percent contribution of upper 10th percentile
daily precipitation to annual total, averaged
over U.S.
from Karl and Knight, 1998
Since 1910, precipitation has increased by about
10 across the contiguous United States. The
increase in precipitation is reflected primarily
in the heavy and extreme daily precipitation
events. For example,over half (53) of the total
increase of precipitation is due to positive
trends in the upper 10 percentiles of the
precipitation distribution.
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Flood Frequency Trends
Number of Floods
Number of People Displaced by Flooding
From Dartmouth
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4XCO2 Flood Frequency Predictions
source Milly et al, 2001
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Current state of climate-change science

• Models can match observed global warming
• Models cant match significant trends or simulate
  precipitation variations is inadequate
• Significant water cycle prediction skill is
  achievable

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• Role of Planetary Atmospheric Boundary Layer in
  Energy and Water Cycle Science
• Interfacial heat, water, momentum, biogeochemical
  flux processes at the heart of coupled Earth
  System variability
• Science Importance of PBL
• Planet is in near radiative balance at TOA, but
  system components are not ? PBL mediates fluxes
  which cool surface, heat atmosphere, dissipate
  momentum.
• PBL rooted clouds (virtually all atmospheric
  convection) are strongly linked with energetics
  of surface fluxes and have large impacts on
  radiative feedbacks.
• Diurnal cycle of PBL important to warm season
  precipitation processes.
• Air quality / aerosol issues of diffusion /
  transport related to PBL ventilation.

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• PBL - Current state of understanding
• We dont understand how moisture and heat fluxes
  from surface control evolution of convection and
  precipitation production. How do we model this
  (convective closure issue)? Basic energy and
  water cycle understanding weakness
• Global models lack resolution and physics to
  handle shallow MBL clouds or diurnal controls on
  cloudiness well ? adverse impact on radiative
  fluxes, optical and IR feedback responses?
  climate projections uncertain.
• Roadblocks to advancement
• PBL transports accomplished by transport
  processes (e.g. mesoscale roll convection)
  subscale to most satellite observations PBL top
  (inversion thickness typically lt 100 m thick ?
  strong vertical gradients not amenable to passive
  remote sensing.
• No global active remote sensing capability to
  place local / regional process studies in
  context.
• Strong coupling between radiation, clouds, PBL
  structure and dynamics means that these processes
  have to be studied together. Computational
  Issue CRMs still too coarse resolution, LES not
  large enough domain.

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Predicting Clouds in climate models 250km
Solar
thermal
 
cloud system 1000km
ice particles
The Cloud/Climate Challenge
latent heat H-bomb
overlap
precipitation
water droplets
convergence
aerosols 0.1um
drizzle
red future observations
yellow current capability
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Why are clouds so tough?

• Aerosols lt0.1micron, cloud systems gt1000 km
• Cloud particles grow in seconds climate is
  centuries
• Cloud growth can be explosive 1
  thunderstorm packs the energy of an H-bomb.
• Cloud properties can vary a factor of 1000 in
  hours.
• Few percent cloud changes drive climate
  sensitivity
• Cloud updrafts are a 100m to a few km.
• Best current climate models are 250km scale.
• Atmospheric fluid dynamics COUPLES all these
  scales (at least gt 100m) and INTEGRATES over
  them.
• A climate model resolving all cloud physics down
  to aerosol scale would require 1038
  supercomputers 190 years of current Moores Law
  rate of advance.
• We have to BE SMARTER than a brute-force attack
  on the problem, and may need a bulk statistical
  theory, like thermodynamics for quantum mechanics.

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Global Water Energy Cycle Advance
Understanding and Model Physics
Climate models grid-box representation of
Earths processes...
Each grid-box can only represent the average
conditions of its area.
However, controlling processes of the water cycle
(e.g. precipitation) vary over much smaller
areas.

• How can climate models effectively represent the
  controlling processes
• of the global water cycle?
• Conventional approach make the model
  grid-boxes smaller (increase resolution)
• Slow progress may take 50 years to be
  computationally feasible
• Breakthrough approach Simulate a sample of the
  small-scale physics and dynamics using high
  resolution process-resolving models within each
  climate model grid-box
• Short-cut the conventional approach (10 years
  to implement)

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Motivation and Methodology

• Assess capability/consistency of rate changes
  in global water cycle detection.
• Assess our global-scale capabilities for
  providing an observed climatology and evaluation
  tool.

• Check for global balance/consistency
• Use optimal amount of satellite-based information
  from disparate data sets which comprise the major
  global water cycle components (i.e. atmos, ocean
  and land)

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Data Synthesis period July,1987-Dec., 1999

• Observationally-based Estimates
• Precipitation (1979-1999) GPCP monthly mean
  gridded data, 2.5 resolution
• Ocean Evaporation (1987-1999) GSSTF2 Global
  Ocean Gridded Data Set - monthly-mean data, SSM/I
  based estimates (Chou et al., 1997), 1
  resolution
• Land Evaporation
• Global Offline Land Dataset (GOLD) 1979-1999
• COLA-SSiB forced by biased-corrected reanalysis
  data (Dirmeyer and Tan, 2001)
• T63 equivalent grid (1.8 resolution)
• Global Soil Wetness Project Phase 2 (GSWP2)
  1986-1995
• Global land models forced with ISLSCP II data at
  1 resolution
• 6 submitted simulations analyzed.
• Total Precipitable Water (1988-1994)
• NASA Global Water Vapor Project (GVAP)

• Model NSIPP AGCM (http//nsipp.gsfc.nasa.gov)
• Resolution 2 by 2.5 degrees, 34 vertical sigma
  layers
• Forced by monthly mean sea surface temperatures
  (SSTs) and sea ice from Reynolds O-I data set
  (Reynolds Smith, 1994).
• Ensemble mean taken from 9 member simulation
  (1930-2000)

For (most of) this analysis, all units converted
to mass (flux)
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Geographic Distribution of Annual P-E (mm)

• Evaporation excess nearly ubiquitous over
  sub-tropical oceans, with a sharp contrast at
  coastal regions.
• Equatorial ocean evaporation minimum consistent
  with other findings (e.g. Seager et al., 2003).
• Tropical land areas show richest excess in
  precipitation.
• Major desert regions, tundra, and mountainous
  regions all indicate deficit to
  marginally-balanced conditions.
• Mid-latitude and boreal coastal/maritime
  environments exhibit adequate precipitation
  supply over evaporation.

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Comparison of Global Fluxes to Previous Estimates

• Global fluxes of precipitation and evaporation
  are comparable to previous century of estimates.
• No discernable trend is seen in both compilations
  of the flux estimates.
• The notable disparity with this study is the
  lower values of both precipitation (not shown)
  and evaporation flux estimates over land.

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Comparison of Global Fluxes to Previous Estimates

• Global fluxes of precipitation and evaporation
  are comparable to previous century of estimates.
• No discernable trend is seen in both compilations
  of the flux estimates.
• The notable disparity with this study is the
  lower values of both precipitation estimates over
  land.

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Comparison of This Study to Previous Estimates
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Annual Variations of Estimated Global Budget

• Notable trend in global evaporation (from ocean)
  of 1/year.
• In any given year, precipitation and evaporation
  are within 10 - but TPW changes would indicate a
  substantially tighter agreement.
• Errors in precipitation preclude assessment of
  evaporation trend.
• Correlation between precipitation and evaporation
  annual variations is low (0.2).
• AGCM correlation very high at 0.99

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Water Energy Cycle Science IssuesPrecipitation
and Evaporation
Schlosser

• Observed averaged annual evaporation and
  precipitation mass flux balance to within 1.
• However, interannual global variations
  considerably uncorrelated.
• AGCM mean rate of annual global water cycle
  exceeds observed (15).
• AGCM interannual variability of annual global
  precip/evap 50/35 lower than observed.
• Relative contributions of land and ocean fluxes
  differ considerably.
• What are the sources of these discrepancies (both
  in the models and observations)?
• Trend in observed global evaporation (1
  /year), but no trend in precipitation.
• Trend in AGCM global water-cycle rate during
  1987-1999 and order of magnitude smaller.
• Source of modeled trend from prescribed SSTs, is
  the response accurate?
• Observations insufficient to detect AGCM trend
  (e.g. Ziegler et al., 2002).

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ROLES OF AGENCIES IN THE WATER CYCLE PROGRAM
UNDERSTANDING NSF, NASA, DOE
USDA USGS APPLICATIONS EPA BoR USACE
PREDICTION NOAA, DOE, NASA
OBSERVATIONS NASA, NOAA (DOE, USGS, USDA)
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Integrated Water and Energy Cycle Research From
Observations to Consequences
Interdisciplinary Research

• Interdisciplinary Linkages
• Aerosols link to precipitation development,
  interaction with energy/radiation cycles
• Carbon link to transpiration and radiation
  absorption
• Weather and Climate water and energy are at the
  heart of weather and climate physics
• Modeling, Assimilation, and Computing essential
  tools for integration and prediction
• Technology development of new observation
  technology
• Applications consequences of change delivered
  through water energy cycle

The availability of new observations strongly
motivates advances in understanding, prediction,
and application.
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Global Water Energy Cycle Linking Science to
Consequences
End-to-end coordination enabling understanding
and prediction of the Earths water cycle system
Research driven by the needs of society
To deliver social, economic and environmental
benefit to stakeholders through sustainable and
appropriate use of water by directing water cycle
science towards improved integrated water system
management
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Land Data Assimilation System (LDAS)
GOAL Produce optimal output fields of land
surface states and fluxes.
SIGNIFICANCE Results will be used for
initialization of weather and climate prediction
models and application investigations.
APPROACH Parameterize, force, and constrain
multiple, sophisticated land surface models with
data from advanced ground and space-based
observing systems.
Assimilation

• Precipitation
• Temperature
• Radiation
• Other variables

LDAS North American LDAS Global LDAS
Root zone soil water content

• Soil Moisture
• Evapotranspiration
• Energy fluxes
• River runoff
• Snowpack
• characteristics

Land Surface Models

• Vegetation Types
• Soil Classes
• Elevation
• Other data

M. Rodell and P. Houser / 974
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• What are the causes of
• water cycle variations?
• Are variations in the global
• and regional water cycle predictable?
• How are water and
• nutrient cycles linked?

NASA-ESE Water Energy Cycle Science Questions
(7 of 24 questions) How are global
precipitation, evaporation and the cycling of
water changing? What are the effects of clouds
and surface hydrologic processes on Earths
climate? How are variations in local weather,
precipitation and water resources related to
climate variation? What are the consequences of
climate change and increased human activities for
coastal regions? How can weather forecast
duration and reliability be improved? How can
predictions of climate variability and change be
improved? How will water cycle dynamics change in
the future?
NASA Water and Energy cycle Study (NEWS)
Challenge Document and enable improved,
observation-based water and energy cycle
consequence predictions (floods and droughts) of
earth system variability and change