Update on LMWG Proposed Hydrologic Improvements to CLM •Overview of proposed hydrology schemes (3) •CAM/CLM and offline CLM simulations – Follow the water •Preliminary conclusions •Validation against tower fluxes Project Objectives: Wetter soils, increased transpiration/photosynthesis, improved partitioning of evapotranspiration and representation of land- atmosphere feedbacks, particularly in the tropics (Amazon)
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Update on LMWG Proposed Hydrologic Improvements to CLM Overview of proposed hydrology schemes (3) CAM/CLM and offline CLM simulations – Follow the water.
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Update on LMWG Proposed Hydrologic Improvements to CLM
•Overview of proposed hydrology schemes (3)
•CAM/CLM and offline CLM simulations – Follow the water
•Preliminary conclusions
•Validation against tower fluxes
Project Objectives: Wetter soils, increased transpiration/photosynthesis, improved partitioning of evapotranspiration and representation of land-atmosphere feedbacks, particularly in the tropics (Amazon)
Summary of Hyd_dlptmcs (NCAR)Interception (decrease) – Reduce fraction of potential intercepted water by ¼.
Transpiration (increase) –Soil moisture stress as in LSM (linear function between optimum and dry soil moisture).
Soil Evaporation (decrease) – Reduce soil-canopy air space conductance.
Surface Runoff (decrease) – Saturated fraction runoff unchanged. Runoff over non-saturated fraction controlled by enhancement factor based on root fraction in top 3 layers (macropores).
Soil Water Dynamics (increase) – Remove exponential decrease in hydraulic conductivity. Depends only on sand content of each layer.
Drainage (increase) – Eliminate saturated and non-saturated fraction drainage. Free drainage from layer 10 controlled by hydraulic conductivity.
Note that Infiltration is a residual of surface water flux - evaporation - surface runoff.
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
RedistributionOcean
Soil Water
Snow
Dra
inag
e
Summary of Hyd_bd_nlai (GIT)
Interception (decrease) – Limit storage capacity and Limit storage capacity and leaf wet fraction by fractional area of liquid leaf wet fraction by fractional area of liquid precipitation (convective rain falls over 10% of precipitation (convective rain falls over 10% of gridcell).gridcell).
Surface Runoff (decrease) – Saturated fraction runoff is exponential function of existing water table scale height. No non-saturated fraction runoff.
Soil Water Dynamics (increase) – Remove exponential decrease in hydraulic conductivity. Depends only on sand content of each layer.
Drainage (increase) – Eliminate saturated and non-saturated fraction drainage. No flux boundary condition at bottom layer. Base flow consists of weighted contributions of freely draining soil and that impeded by coupling to water table and applied to bottom layer . Water table depth based on lowest saturated layer and soil matric potential.
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
RedistributionOcean
Soil Water
Snow
Dra
inag
e
Summary of Hyd_nli
Interception (decrease) – Reduce fraction of potential intercepted water by fractional area of precipitation (convective precip falls over 10% of gridcell)(convective precip falls over 10% of gridcell). Leaf wet fraction unchanged. Applied to convective snow as well.
Surface Runoff (decrease) – Saturated fraction runoff is exponential function of water table depth. Max saturated runoff provided by topographic index.
Soil Water Dynamics (increase) – Exponential decrease in hydraulic conductivity but enhanced by factor of seven.
Drainage (increase) – Eliminate saturated and non-saturated fraction drainage. No flux boundary condition at bottom layer. Excessive water above saturation added to above unsaturated layer. Base flow based on maximum baseflow parameter and exponential function of water table depth and applied to all layers.
CAM3/CLMx - Follow the water
Ocean
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx - Follow the water
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
Redistribution
Soil Water
Snow
Dra
inag
e
CAM3/CLMx Global Land Annual Average
Photosynthesis
65
100115
158142 143
120
-101030507090
110130150170190
Pg
Partitioning of Evapotranspiration
010203040506070
%
Transpiration Ground Evap Canopy Evap
Partitioning of Runoff
00.10.20.30.40.50.60.7
Su
rfac
e R
un
off
Rat
io
0.7
0.75
0.8
0.85
0.9
To
tal R
un
off
(m
m/d
ay)
Surface Runoff Ratio Total Runoff
Hydrologic Cycle
0.5
1
1.5
2
2.5
Hyd_c
on
Hyd_s
unsh
a
Hyd_p
law_p
lsc
Hyd_d
lptm
cs
Hyd_n
li
Hyd_b
d_nlai Obs
mm
/da
y
Precipitation Evapotranspiration Runoff
CAM3/CLMx
River Discharge to Ocean
Offline CLM (“Examining the simulated hydrology under biased
forcings makes no sense”)
Atmospheric forcing courtesy of T.Qian/A. Dai - NCAR
CAM3/CLMx
Discharge for World’s Top 10 RiversOffline CLM
CAM/CLMx Climate Changes
CAM/CLMx Climate Changes
CAM3/CLMx
CAM3/CLMx Volumetric Soil Moisture
Conclusions• All schemes (in combination with sun/shade model and new surface datasets) offer
substantial improvements in producing wetter soils, increasing transpiration and photosynthesis, and improving the partitioning of evapotranspiration.
• Hyd_dlptmcs and Hyd_bd_nlai are most similar in terms of partitioning of evapotranspiration and surface runoff ratio. Globally, Hyd_nli has less transpiration and canopy evaporation, more ground evaporation, lower surface runoff ratio than the other two schemes.
• All schemes produce reasonable river discharge to ocean compared to observations.
• In the Amazon, all schemes improve temperature and precipitation biases and hydrologic cycle.
• In general, the three schemes produce similar but small changes in climate. The most notable exceptions to this are:
– All schemes produce cooling in Arabian Peninsula and India in DJF (undesirable) with Hyd_nli resulting in the largest cooling
– Increase in wet season precipitation in the Amazon in all schemes (desirable) and an enhanced seasonal cycle in the Congo (undesirable).
– In JJA, all schemes produce cooling in Europe and near Caspian/Black seas, most of U.S., and Amazon (desirable). All schemes increase positive bias in precipitation in Arabian Peninsula and southern India (undesirable).
Conclusions
• All schemes require minimal software engineering for implementation and only small changes to documentation (tech note)
• All schemes have free parameters that could be “tuned”.
• Final optimal scheme will likely consist of some combination of desirable aspects of each scheme. How to determine this requires more testing against observations and a deeper understanding of why each scheme performs as it does.
EXTRA SLIDES
Hydrology
Canopy Water
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface Runoff
Evaporation
Transpiration
Precipitation
RedistributionOcean
Soil Water
Snow
Dra
inag
e
Summary of Hyd_con (CAM3/CLM3)Interception – Fraction of potential intercepted water is an exponential function of leaf and stem area.
Transpiration – Soil moisture stress is a non-linear function of root distribution and soil water potential.
Soil Evaporation – Soil-canopy air space conductance is a weighted function of bare soil and dense canopy conductances where weights depend on leaf and stem area.
Surface Runoff – Sum of runoff from saturated and unsaturated fractions which are determined from a water table scale height (conceptual TOPMODEL).
Soil Water Dynamics – Exponential decrease in hydraulic conductivity.
Drainage (increase) – Sum of drainage from saturated and non-saturated fractions plus drainage from layer 10 controlled by hydraulic conductivity.
Note that Infiltration is a residual of surface water flux - evaporation - surface runoff.