LandClimate Interactions

1
Land/Climate Interactions
Lecture 1 Global Hydrology
A walking tour through the global water cycle,
with an emphasis on complicating and/or
unresolved research issues.
2
Issue Imperfect knowledge of the
globally-averaged fluxes.
Two different estimates (even after
normalization)
3
Issue The components of the water cycle operate
at different timescales...
4
and different spatial scales
A Plan for a New Science Initiative on the
Global Water Cycle, USGCRP, 2001
Opportunities in the hydrologic sciences,
National Academy Press, 1991
5
Issue The global water balance is inextricably
tied to the global energy balance.
latent heat release during condensation in
atmosphere
6
Issue measurements of the global water balance
are far from perfect.
Precipitation, a relatively well-measured
hydrological field, is still not known with
certainty.
Two alternative, state-of-the-art estimates
disagree in places
7
1. Precipitation events can easily be missed by
raingauges. 2. Structure of precipitation events
is critical. In these events, the average rain
depth over the catchment is about the same, yet
the hydrological response will differ markedly.
Fennessey et al., Ralph M. Parsons Tech Report
307, MIT, 1986
8
Evaporation, a critical element of the
hydrological cycle, can only be roughly estimated
on the global scale.
One approach determine evaporation by forcing a
land surface model with observed meteorological
data
9
In situ soil moisture measurements are spotty and
are not global. Satellite soil moisture
measurements are global but only access the top
millimeters of soil. Modeled soil moisture
reflects observed antecedent forcing but is
limited by realism of model used.
Global Soil Moisture Data Bank
http//climate.envsci.rutgers.edu/soil_moisture/in
dex.html
10
Validation Standard Error3
Soil Moisture Mapping and Single Channel
Algorithm Validation Using ESTAR in SGP97
11
Satellite vs. model surface soil moisture
(1979-87)
12
Runoff integrates hydrological response over
large areas. Data is not compete, however, and
communication between data centers is less than
perfect.
Active streamgages operated by the
USGSStreamgages currently operated by other
agencies and in the NSIP planStreamgages that
are inactive, to be reactivated in the NSIP
planProposed new streamgages in NSIP Plan
Global Runoff Data Center
13
Issue realistic modeling is difficult.
Simple models of soil moisture transport,
commonly used in todays models...
ignore tremendous complexity below the surface
100s of km
14
Nevertheless, different models, forced with the
same met. data, produce different evaporation
rates.
Models often go to great lengths to characterize
the evaporation process properly.
Bowling, PILPS 2-e
15
Two critical roles for a land surface model
Partition incoming radiative energy into latent
heat, sensible heat, heat storage, and outgoing
radiative energy Partition precipitation into
evaporation, runoff, and water storage.
Proper land surface modeling has many potential
benefits. It will be the focus of much of the
first part of this course.
16
Precipitation, a relatively well-measured
hydrological field, is still not known with
certainty.
Two alternative, state-of-the-art estimates
disagree in places
GCMs can be way off!
17
Different AGCMs
OBS
18
Issue variations in the global water cycle can
have tremendous impacts on society, yet they
often cant be predicted.
1) Floods
During 1991-1995, flood related damage totaled
more than US200 billion (not inflation adjusted)
globally, representing close to 40 of all
economic damage attributed to natural disasters
in the period. (Pileke Jr. and Downton, 2000,
citing IFRCRCS, 1997)
1993 Mississippi River flood
19
Impacts of floods and droughts have been known
for a long time...
2) Droughts
Droughts can be expensive --1988 midwest
drought 40 billion -- 1998 southern U.S.
drought 6 to 9 billion
Drought near Bracketville, Texas, in 1980
20
Predictions of water cycle variations, however,
are gradually becoming better, largely through
the development of earth system models and
improved understanding of phenomena like El Nino.
prediction
observed
21
Background photograph (taken by Philipp
Hoelzmann) shows rock paintings of mid-Holocene
fauna near Zolat el Hammad, North Sudan. Today
this region, like the largest part of the Sahara,
is a hyperarid desert. The desert formed some
5,000 to 6,000 years ago. Ensemble simulations
using a coupled atmosphere-ocean-vegetation model
reveal a rather abrupt change in Saharan
vegetation (superimposed blue lines indicate
fractional vegetation cover), which was triggered
by subtle changes in Northern hemisphere summer
insolation (Claussen et al.,1999).
Issue because our observational record is
limited, we dont have a full characteriza-tion
of the variability of the water cycle -- we dont
necessarily know what nature will throw at us in
the years to come.
A Plan for a New Science Initiative on the
Global Water Cycle, USGCRP
Figure 2. Winter-spring precipitation
reconstructed from tree ring data, Durango,
Mexico (normalized and smoothed to highlight
decennial variability). The tree-ring estimates
explain 56 of the variance in precipitation for
Durango and are consistent with independent
precipitation data. This reconstruction is well
correlated with the all-Mexico rainfall index (r
0.76 p lt 0.001) and with precipitation over
north central Mexico, where the cocoliztli
epidemics appear to have been most severe. Note
the unprecedented 16th-century megadrought during
both cocoliztli epidemics.
Megadrought and Megadeath in 16th Century Mexico,
Rodolfo Acuna-Soto, David W. Stahle, Malcolm
K. Cleaveland, and Matthew D. Therrell
22
Issue certain components of the global water
cycle contain information about past climate.
Ice cores
Groundwater
Phillips et al., 1986
23
Issue Humans may be modifying the global water
cycle in significant ways.
Stan Leake and Dave Goodrich, viaA Plan for a
New Science Initiative on the Global Water
Cycle, USGCRP
24
Observations Glacier Extent
1986
1973
Retreat of Muir Glacier, from Landsat
25
Global warming may or may not be affecting or
even accelerating Earths hydrological cycle.
Some evidence is suggestive...
whereas other evidence appears to fly in the
face of model predictions.
26
Issue predictions often are made at large
scales, but sociological impacts tend to occur at
much smaller scales. How do we translate
predictions between scales?
Nesting climate and hydrologic models. A coupled
ocean-atmosphere model is used to compute global
sea surface temperatures (SSTs), which are
transferred as input, along with the land-surface
state, to a global atmospheric model. The global
model output drives a large-scale atmospheric
circulation model, whose output serves as an
input to a regional atmospheric dynamics model.
This regional model computes surface temperature,
precipitation, and other radiation components
which, when spatially disaggregated, and upon
specifying the land state again at basin
resolution, provide the input for a basin-scale
coupled hydrology-ecosystem model. The hydrologic
model predictions along with risk statistics can
provide input to a complex decision making
process. Shukla staircase, printed inA Plan
for a New Science Initiative on the Global Water
Cycle, USGCRP, 2001
27
Issue the global water cycle is strongly tied to
global geochemical cycles.
Water is the universal solvent.
Societal Need Understanding the links among the
C, N, and water cycles in terrestrial and inland
aquatic systems and the factors driving the human
activities that impact vegetation distribution
and water quality.
A Plan for a New Science Initiative on the
Global Water Cycle, USGCRP
28
La Conchita mudslide, January 2005
(photo taken off web. AP?)
29
Issue the global water cycle is strongly linked
to global ecological distributions.
Wang and Eltahir
Eagleson and Segarra
http//www.tkl.iis.u-tokyo.ac.jp/RGOE/actual.html
30
Issue the global water cycle is a strong control
on human society.
Annual precipitation field
Population density
Oki, 2002
31
Issue the global water cycle includes the ocean.
The terrestrial branch of the water cycle can
affect the ocean circulation.
32
Issue How do we take best advantage of the new
kinds of data (particularly satellite data) now
being made available?
33
Issue Hydrological science may have
extraterrestrial relevance!
Methane river channels on Titan
European Space Agency scientists report the
first look at data from Huygens' descent and
landing on Titan shows the Saturnian moon has
Earth-like geophysical processes operating on
exotic materials in very alien conditions. (Jan.
21)
34
A Plan for a New Science Initiative on the
Global Water Cycle by the USGCRP Water Cycle
Study Group
Three science questions 1. What are the causes
of water cycle variations on global and regional
scales? 2. To what extent are these variations
predictable? 3. How are water and nutrient cycles
linked? Three pillar initiatives 1. Determine
whether the global water cycle is intensifying
and, if so, to what degree human activities are
responsible. 2. Extend the science to decrease
the costs of water cycle calamities (droughts,
floods, eutrophication, etc.) 3. Develop the
ability to predict the effects of changes in land
use, land cover, and cryospheric processes on the
cycling of water and associated geochemical
constituents.
35
Lectures
Intro Land Climate / Global Hydrology The
Surface Energy BalanceThe Surface Water
Balance Radiation Turbulence Land Surface
Parameterizations (part 1) Land Surface
Parameterizations (part 2) Land Surface
Parameterizations (part 3)Comparisons of LSMs
Land and Climate Modeling Studies Land and
Climate Observational Studies Land Use Land
Cover Change Natural Variability of the Land
Surface Long-Term Vegetation Changes
Introduction

Basic constraints on land surface behavior
simple modeling approaches.

Structure and performance of land surface models
used with todays GCMs.

Role of the land surface in the climate system.