Mississippi River Basin

1
Mississippi River Basin Since 1948 there have
been striking changes in many meteorological
variables. Surprisingly, many can be described by
linear trends Precipitation ? Runoff ?
Cloud ? Diurnal Temperature Range DTR
? Sunshine (dimming) ? Dimming has led some
researchers to deduce that evapotranspiration ET
may have decreased. But increased rainfall and
soil moisture imply greater latent vs sensible
heating and increased ET.
2
Mississippi River Basin Has ET increased or
decreased? Can we satisfy BOTH the heat and
water budgets?
Tools Community Land Model 3 CLM3 Global, T42
and 0.5? grid Observations of some
variables Result an observationally constrained,
physically consistent view of changes over time.
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Mississippi River Basin Observations Monthly
mean Temperatures CRU, NCDC DTR
NCDC Precipitation (Chen et al, GPCP) Streamflow
(Vicksburg, MI) Surface cloud High frequency
(within month) from NRA, similar to
ERA-40 Relative humidity from NRA Verification S
olar radiation Soil moisture
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W Soil liquid and ice moisture, snow moisture,
canopy moisture P precipitation E
Evapotranspiration R Runoff, surface and
subsurface G Ground heat flux (incl snow) LH
latent heat SW Shortwave LW Longwave LH ? E
Water Budget dW/dt P - E - R Energy
Budget G SW - LW - SH - LH.
RT
SH
LE
Rs
LP
Fs
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Divergence of atmospheric moisture is balanced by
E-P and change in atmospheric storage
E P
Runoff
Soil moisture
Divergence of surface moisture runoff is
balanced by E-P plus change in soil moisture
storage
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Anomaly time series for annual (water-year)
Surface air temperature (CRU red) and (GHCN2
black dashed) Diurnal Temperature Range
(DTR, scaled as 5DTR5, Cloud cover (CLD) and
cloud-adjusted downward solar radiation (SW?,
increases downward right ordinate)
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Time series of annual (water-year) surface water
budget components and linear trends ( b in mm
yr-1/decade for all except for W in mm/decade).
Precipitation observed (P), Runoff observed
(Robs) Runoff model (CLM3) (R) EB the water
budget-derived evapotranspiration E model
(CLM3) dW/dt change of land water storage (note b
for this quantity is d(dW/dt)/dt) W water storage
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Annual (water-year) surface energy budget And
trends (b in W m-2 decade-1).
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Mississippi River Basin
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Precip Runoff Evap
Storage Temp Cloud
Linear trends October 1948-September 2004
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SW LH LW SH Net
radiation SHLH
Linear trends October 1948-September 2004
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Mississippi River Basin
M is the long-term (1948-2004) annual
(water-year) mean mm yr-1 for water components
W m-2 for energy components b annual linear
trend 1948-2004 mm yr-1/decade for water W
m-2/decade for energy (proportional to arrow
shaft width). Note that the downward arrow
means that the flux increases the trend of dW/dt
or G.