Andes-Amazon Project: Hydrology Model-Data Intercomparison Brad Christoffersen Nov. 08, 2010 Moore Foundation

Key Questions Water budget partitioning The case of CLM & modifying hydrology structure Was soil physics standardization across models effective? Do models capture observed ET, runoff partitioning (Manaus site)? Soil moisture dynamics across models Are remaining model differences due to physics, or biology? Are vertical gradients & seasonal variability corroborated by observations?

Hydrology in CLM3.5 Oleson et al., 2008, JGR water table depth When W a = W a,max = 5000 mm, water table depth = depth of the bottom soil layer When water table is below the soil column One additional water storage variable: W a

Modified CLM3.5 per Site Simulation Protocol Oleson et al., 2008, JGR water table depth –> Aquifer storage held const = 0

Modified CLM3.5 per Site Simulation Protocol Oleson et al., 2008, JGR water table depth –> Aquifer storage held const = 0 --> Water table depth const > 10 m Zwt = constant

Modified CLM3.5 per Site Simulation Protocol Oleson et al., 2008, JGR water table depth –> Aquifer storage held const = 0 --> Water table depth const > 10 m --> Drainage out bottom layer = hydraulic conductivity of bottom layer Free drainage (= kbot) Zwt = constant

Modified CLM3.5 per Site Simulation Protocol Oleson et al., 2008, JGR water table depth –> Aquifer storage held const = 0 --> Water table depth const > 10 m --> Drainage out bottom layer = hydraulic conductivity of bottom layer --> Soil depth set from 3.5 m to site soil depth Free drainage (= kbot) Zwt = constant

Modifying hydrology: The case of CLM

CLM3.5 Aquifer 3.5 m soil depth Correct ET seasonality (wrong reason?) Modifying hydrology: The case of CLM Surface Runoff Subsurface Runoff

CLM3.5 Free drainage 3.5 m soil depth CLM3.5 Aquifer 3.5 m soil depth Incorrect ET seasonality (what's missing?) Correct ET seasonality (wrong reason?) Modifying hydrology: The case of CLM Surface Runoff Subsurface Runoff

CLM3.5 Free drainage 8m soil depth CLM3.5 Free drainage 3.5 m soil depth CLM3.5 Aquifer 3.5 m soil depth Correct ET seasonality (right reason?) Incorrect ET seasonality (what's missing?) Correct ET seasonality (wrong reason?) Modifying hydrology: The case of CLM Surface Runoff Subsurface Runoff

Was soil physics standardization effective? JULESED2IBIS CLM Similar pattern & magnitude of water budgets JULES, IBIS, CLM potentially overestimate ET Manaus K34 - Yes! Surface Runoff Subsurface Runoff

JULESED2IBIS CLM Evergreen Tapajos K67

JULESED2IBIS CLM Evergreen Tapajos K67 Transitional/Semideciduous Reserva Jaru

JULESED2IBIS CLM Evergreen Tapajos K67 Transitional/Semideciduous Reserva Jaru Savanna Pe de Gigante

OBS Data from Tomasella & Hodnett 2008 JULESED2IBIS CLM OBS Are predicted budgets consistent with observations? (Manaus K34)

Interlude: Model structure I Infiltration/Surface Runoff: JULES: Infiltration excess + PFT-dependent infiltration “enhancement factor” ED2: Infiltration excess + Surface water storage (8- hour lifetime) IBIS: Green-Ampt wetting front CLM: Infiltration excess + Maximum ponding depth (10 mm H2O)

Interlude: Model structure I Infiltration/Surface Runoff: JULES: Infiltration excess + PFT-dependent infiltration “enhancement factor” ED2: Infiltration excess + Surface water storage (8- hour lifetime) IBIS: Green-Ampt wetting front CLM: Infiltration excess + Maximum ponding depth (10 mm H2O) theta.i theta.s water soil wetting front psi = H z = 0 z = f Green-AmptStandard Darcy ponding depth theta.1, theta.1.sat 1 2 3

Interlude: Model structure II Rooting dynamics and water extraction: JULES, CLM (& IBIS?): proportional to water availability & root fraction in each soil layer ED2: proportional to water availability and maximum rooting depth (by veg. cohort) Consider special case: Homogeneous soil water profile, (& for ED); mid- to late-successional forest:

Interlude: Model structure II Rooting dynamics and water extraction: JULES, CLM (& IBIS?): proportional to water availability & root fraction in each soil layer ED2: proportional to water availability and maximum rooting depth (by veg. cohort) Consider special case: Homogeneous soil water profile, (& for ED); mid- to late-successional forest: Fraction of transpiration Depth (m) JULES, CLM (& IBIS?) ED2 0 1

Soil Moisture Dynamics: Are remaining differences due to physics or biology? JULESED2IBIS CLM Green-AmptDarcy's Law Free drainage Other mechanisms? Free drainage INFILTRATION BOTTOM BOUNDARY Manaus K34

JULESED2IBIS CLM K67 RJA PDG

What happens in CLM when we implement an ED-like root water uptake scheme?

Free drainage soil depth 8 m Root distribution-dependent water stress Free drainage soil depth 8 m Root distribution-independent water stress

Summary & Conclusions Overall water balance: Encouraging. (Standardization of surface runoff necessary?) ET Seasonality: All models predict peak of transpiration in dry season; some (ED) predict constant ET year-round. Soil moisture dynamics: Interesting, important differences among models. IBIS has much higher surface water content ED develops wet season pool near bottom boundary Discriminating among model mechanisms: Vertical profiles of root water uptake needed (esp. under drought!) Existing soil moisture datasets: Potentially a powerful tool to discriminate among model mechanisms of root water uptake.