Geophysical Fluid Dynamics Laboratory Review

May 20 – May 22, 2014

Presented by

Hydrology

Chris Milly

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

Hydrology: Preview

①Land model LM3, used in all GFDL CMIP5

streams, contains new physical/hydrologic

features that

• improve fluxes to atmosphere and oceans;

• support terrestrial biogeochemical modeling;

• represent impact-relevant hydrologic variables (streamflow, lake levels, water table).

②A focus on potential evapotranspiration (PET)

helps reconcile conflicting projections of

water availability and drought.

1

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

LM3 Hydrology: Features

2

soil-veg column (tile)

lake tile

landscape unit

grid cell

river network

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

lake

leve

ls

LM3 Hydrology: Stand-Alone Evaluation

3

annual range of water storage (mm)

LM3 storage variables compare well with observations.

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

LM3 Hydrology: Evaluation

4

permafrost extent

late

nt

hea

t fl

ux

Observations

LM3

DICE: Diurnal Land/Atmosphere Coupling Experiment

(credit: Adrian Lock, Martin Best)

LM3 reproduces permafrost extent well.

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

Work in Progress: Toward LM4

5

Hill-slope tiling (Subin) Urban tiling

+ Higher Resolution + Biogeochemistry (Shevliakova)

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

Potential Evapotranspiration

6

Climate

Projections

Empirical Relations

(e.g., Thornthwaite)

Hydrologic Models,

Drought Metrics

(e.g., PDSI)

P

T PET Water

Projections

Many hydrologic impact analyses have PET as a

pivotal link:

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

Potential Evapotranspiration

7

• In a case study, PET change

had been overestimated by a

factor of ~3 vs. that implicit in

the climate model.

• Substantial negative bias in

runoff change results.

• SREXAR5: “AR4 conclusions

regarding global increasing

drought since the 1970s were

probably overstated.”

y = 3.0x

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.2

Relative Change in PET

climate model

hyd

rolo

gic

mo

del

(after Milly and Dunne [2011])

Geophysical Fluid Dynamics Laboratory Review

May 20-22, 2014

Hydrology: Recap

①Land model LM3, used in all GFDL CMIP5

streams, contains new physical/hydrologic

features that

• improve fluxes to atmosphere and oceans;

• support terrestrial biogeochemical modeling;

• represent impact-relevant hydrologic variables (streamflow, lake levels, water table).

②A focus on potential evapotranspiration (PET)

helps reconcile conflicting projections of

water availability and drought.

8