Modeling of land hydrology with the use of topographical features

 V.N.Krupchatnikoff and A.I.Krylova

 

Institute of Computational Mathematics and Mathematical Geophysics SB RAS, Novosibirsk, Russia

e-mail: vkrup@ommfao1.sscc.ru, alla@climate.sscc.ru 

IntroductionIntroduction An anthropogenic changes in atmospheric An anthropogenic changes in atmospheric

composition are expected to cause climate composition are expected to cause climate changes: increasing surface temperature, changes: increasing surface temperature, intensification of the water cycle with a intensification of the water cycle with a consequent increase of frequency of flood consequent increase of frequency of flood Output from 900-yr “control” (constant radiative Output from 900-yr “control” (constant radiative forcing) experiment with coupled ocean-forcing) experiment with coupled ocean-atmosphere-land model has been used to atmosphere-land model has been used to evaluate flood risk (P.C.D. Milly, R.T. Wetherald, evaluate flood risk (P.C.D. Milly, R.T. Wetherald, K. A. Dunne, T.L. Delworth, 2002)K. A. Dunne, T.L. Delworth, 2002)

Focus of this work to prepare new version of the Focus of this work to prepare new version of the surface hydrology with topography-based runoff surface hydrology with topography-based runoff scheme to produce topography – related runoff scheme to produce topography – related runoff and river discharge in coupled atmosphere-land and river discharge in coupled atmosphere-land model (INM/RAS – ICMMG/SB RAS)model (INM/RAS – ICMMG/SB RAS)

Model DescriptionModel Description

AGCM/INM RAS 5x4 horizontal AGCM/INM RAS 5x4 horizontal resolution and 21-level vertical resolution and 21-level vertical resolution (Alexeev V., E.Volodin, resolution (Alexeev V., E.Volodin, V.Galin, V. Dymnikov, V. Lykosov, 1998)V.Galin, V. Dymnikov, V. Lykosov, 1998)

LSM/ICMMG SB RAS - biophysical and LSM/ICMMG SB RAS - biophysical and biochemical surface model (V. biochemical surface model (V. Krupchatnikov, 1998Krupchatnikov, 1998))

Terrain-following vertical coordinate (21 Terrain-following vertical coordinate (21 σ-σ-levels)levels) Semi-implicit formulation of integration in timeSemi-implicit formulation of integration in time Energy conservation finite-difference schemes Energy conservation finite-difference schemes

(5(5x 4) x 4) (Arakawa-Lamb,1981)(Arakawa-Lamb,1981)

Convection (deep, middle, shallow)Convection (deep, middle, shallow) Radiation (H2O, CO2, O3, CH4, N2O, O2; 18 Radiation (H2O, CO2, O3, CH4, N2O, O2; 18

spectral bands for SR and 10 spectral bands for spectral bands for SR and 10 spectral bands for LR) LR)

PBL (5 PBL (5 σ-σ-levels)levels) Gravity wave drag over irregular terrainGravity wave drag over irregular terrain

1. Atmospheric model (INM/RAS):1. Atmospheric model (INM/RAS):

2.2. Land Land surfacesurface model(ICM&MG/SB RAS): model(ICM&MG/SB RAS):

Vegetation composition, structureVegetation composition, structure Radiative fluxesRadiative fluxes Momentum and energy fluxesMomentum and energy fluxes Vegetation and ground temperatureVegetation and ground temperature Soil and lake temperatureSoil and lake temperature Surface hydrology (snow, runoff, soil water, canopy Surface hydrology (snow, runoff, soil water, canopy

water etc.)water etc.) CO2 emissions from terrestrial vegetationCO2 emissions from terrestrial vegetation CH4 emissions from natural wetlandsCH4 emissions from natural wetlands

Структура ячейки сетки в модели Структура ячейки сетки в модели поверхностиповерхности

Плотность листового индекса в модели Плотность листового индекса в модели поверхностиповерхности

Структура и состояние растительного Структура и состояние растительного покровапокрова

Global Net CO2 fluxes(mmol CO2/m^2 c), Global Net CO2 fluxes(mmol CO2/m^2 c), (coupled simulation)(coupled simulation)

CH4 emissions from natural wetlands (coupled CH4 emissions from natural wetlands (coupled framework)framework)

West Siberia West Siberia

Модель биосферы поверхности земли Модель биосферы поверхности земли прогнозирует:прогнозирует:

Vegetation composition, structureVegetation composition, structure

(периодически сезонно меняющаяся) - (периодически сезонно меняющаяся) - нетнет Radiative fluxesRadiative fluxes - - дада Momentum and energy fluxesMomentum and energy fluxes - - дада Vegetation and ground temperatureVegetation and ground temperature - - дада Soil and lake temperatureSoil and lake temperature - - дада Surface hydrology (snow, runoff, soil water, Surface hydrology (snow, runoff, soil water,

canopy water etc.)canopy water etc.) - - дада CO2 emissions from terrestrial vegetationCO2 emissions from terrestrial vegetation - - дада CH4 emissions from natural wetlandsCH4 emissions from natural wetlands - - дада

Estimates of 100-yr flood discharges based on model and observations

( P.C.D. Milly, R.T. Wetherald, K. A. Dunne, T.L. Delworth, 2002 )

ECHAM4 and HadCM3 climate modelsECHAM4 and HadCM3 climate modelsEffect on river discharge of increasing surface Effect on river discharge of increasing surface

temperaturetemperature

Results. INM/RAS-ICMMG/SB RAS coupled model Results. INM/RAS-ICMMG/SB RAS coupled model responseresponse

1. The topography-based hydrological model (TOPMODEL) 

By using the a priori computed topography index of a catchment and average water storage deficit calculated in the drainage, TOPMODEL directly estimate spatial distributions of the groundwater table and local water storage deficit in the unsaturated zone, and predict the portion of area in the catchment where saturation excess runoff will occur:

.

tanln

amss

...

In TOPMODEL total streamflow is the sum of saturation overland flow and subsurface flow .

Saturation overland flow is the sum of direct precipitation on saturated areas and return flow  .

subsurfaceoverlandtotal QQQ

returndirectoverland QQQ

Direct runoff flow is generated when precipitation falls on a saturated area:  Asat is calculated by computing s at any point. If s is less than or equal to zero, the soil is completely saturated and any rain on the surface will become direct overland flow. This occurs most easily for points within the catchment where the topographic index is large. Return flow occurs where s is less than zero. The return flow is given by:

.. .

PAQ satdirect

satreturn AsQ

To compute the mean subsurface discharge, qsubsurface is integrated along

the length of all stream channels and divided by the catchment area: 

or .

dLeTA

qL

m

s

subsurface

tan

10

m

s

subsurface eeTq

0

2. Topography-related runoff model2. Topography-related runoff model

2.1. Saturated hydraulic conductivity

In the ICM&MG land-surface model, the soil moisture is calculated at the interface level of the model layers

, .

For the i- th layer , . Hydraulic conductivity at saturation ksat vary with percent of sand according

to , where and can be determined through optimization procedures.

12/1

12/12/1

i

iiii z

kq

11

2/12/1 //

2

iiii

ii kzkz

zk

sat

isati kk

b

sat

satsati

100070556.0)0(satk

2.2. Bottom drainage

The gravitational loss of soil water from the bottom of the model soil column is given by the following: for bottom layer i=6 ,

66

666

d

dkkq n

2.3. Saturation excess 

The soil water may exceed the physical constraints. Any soil in excess of saturation   

exisati Wz is added to the soil, starting at the top of the soil layer.

If a column becomes oversaturated, the subsurface runoff due to a saturation excess is 

tzR isatisbsat /,0max,

The water table depth zwt is used to determine a saturated function, a surface

runoff and a baseflow. The water table depth zwt is computed by the iterative solution of the

equality

.. /;;;;;;; …… ……………………..

dzzWwtz

satex 0

)(

2.4. Subsurface runoff

The subsurface runoff is parameterized in the form where is a subsurface runoff due to the topographical control (calculated by the TOPMODEL), is the bottom drainage, and is a saturation excess.

exsubdrainsubsubsub RRRR ,,,

,subRdrainsubR , exsubR ,

2.5. Topographical control The subsurface runoff due to the topographical control is given by  , where is a factor with allowance for a difference in the saturated hydraulic conductivity in the lateral and the vertical directions.  

)(,

)0(wtsat fz

sub ef

KR

3. The river discharge model

Using linear advection scheme at 100 resolution river rout water model from one cell to its downstream neighboring cell by considering balance of horizontal water inflows and outflows:  , where is divergence source of river water, , is the effective water flow velocity ; Wriv is storage of stream water within

the cell (m3).

RFFt

Woutiin

riv

,

rivr

out Wl

F

dlrr

r

Figure 2. Upscaling function for obtaining 10' equivalent of a topographic index from its values for 30-arc-second DEM

01

03

0301 62.107.0

Figure 1. ln(a/tan b) distribution function computed from GTOPO30 DEMs for the Tom river basin

Figure 3. Seasonal water discharge of the Tom river. The solid line – the model result (off-line simulation). Clauster of lines – observations of discharge for period of 1965-1984 years.

ConclusionConclusion

Total runoff (surface and sub-surface drainage) is routed Total runoff (surface and sub-surface drainage) is routed downstream to oceans using a river routing model. River downstream to oceans using a river routing model. River routing model is based on TOPMODEL ideasrouting model is based on TOPMODEL ideas

    A river routing model is coupled to the Land Surface Model A river routing model is coupled to the Land Surface Model (ICMMG SB RAS) for hydrological applications and for improved (ICMMG SB RAS) for hydrological applications and for improved land-ocean-sea ice-atmosphere coupling in the Climate System land-ocean-sea ice-atmosphere coupling in the Climate System Model (CSM). Model (CSM).

  We have implemented this model (off-line)We have implemented this model (off-line) on a 1-degree grid. on a 1-degree grid. Land model interpolates the total runoff from the column Land model interpolates the total runoff from the column hydrology (2.8 by 2.8 degree) to the river routing 1-degree grid. hydrology (2.8 by 2.8 degree) to the river routing 1-degree grid.

    Pictures we shown here are results from a regional 1° by 1° Pictures we shown here are results from a regional 1° by 1° simulation (River Tom basin) using global ICMMG LSM. The simulation (River Tom basin) using global ICMMG LSM. The model is driven with AMIP data from 1979 to 1993.model is driven with AMIP data from 1979 to 1993.

Thank youThank you