The Link between Soil Moisture and Drought as Examined in DRI

Transcription

1 The Link between Soil Moisture and Drought as Examined in DRI John Pomeroy Centre for Hydrology Department of Geography University of Saskatchewan, Saskatoon

2 THE TEAM Co-leads leads: Ron Stewart (PI, McGill) ) and John Pomeroy (Sask( Sask) Network Manager: Rick Lawford (Manitoba) Information Managers: Matt Regier (HAL, EC), Patrice Constance (Ouranos) Investigators (13): Bonsal (Sask/NHRC( Sask/NHRC), Bullock (Man( Man), Gyakum (McGill( McGill), Hanesiak (Man( Man), Hayashi (Calg( Calg), Leighton (McGill( McGill), Lin (McGill( McGill), Pietroniro (Sask/NHRC( Sask/NHRC), Snelgrove (Memorial)( Memorial),, Strong (Alta), van der Kamp (Sask/NHRC( Sask/NHRC), Wheaton (Sask/SRC( Sask/SRC), Woodbury (Man( Man) Collaborators (+14): Boer (MSC( MSC), Caya (Ouranos), Derome (McGill( McGill), Derksen (MSC), Donaldson (MSC( MSC), Granger (NHRC( NHRC), Martz (Sask( Sask), Raddatz (MSC( MSC), Ritchie (MSC( MSC), Shabbar (MSC), Sills (MSC), Smith (MSC( MSC), Szeto (MSC( MSC), Walker (MSC( MSC), more.. Research expertise covers critical areas for DRI Solid track record of working together as well as being in and leading l networks

3 OBJECTIVE OF DRI To better understand the physical characteristics of and processes influencing Canadian Prairie droughts, and to contribute to their better prediction, through a focus on the recent severe drought that began in 1999

4 DRI THEMES 1. Quantify the physical features, flows of water and energy into and out of the region, and storage and redistribution within the region 2. Improve the understanding of processes and feedbacks governing the formation, evolution, cessation and structure of the drought 3. Assess and reduce uncertainties in the prediction of drought 4. Compare the similarities and differences of current drought to previous droughts and those in other regions 5. Apply our progress to address critical issues of importance to society

5 1. QUANTIFY THE DROUGHT Observational Networks Surface Storage Change 200 m GRACE satellite Many Springs Crestomere Lake Gull Lake Ponoka Sylvan Lake Red Deer Dickson DamInnisfail Olds Calgary Elnora Irricana OkotoksHigh River Pine Lake Carseland Buffalo Lake Buffalo Lake DrumhellerHand Hills Cluny Stettler Kirkpatrick Lake Sounding Creek Sibbald Big Stone Gem Cessford Buffalo North Duchess Cavendish Tyner Duck Lake Hague Warman Saskatoon Saskatoon Vanscoy Blucher Swanson Conquest Bruno Enchant Barons Medicine Hat Mud Lake Orton Lethbridge Oldman Dam Forty Mile Coulee Elkwater Warner Pakowki Cypress Verlo Instow Shaunavon Swift Current Smith Coulee Del Bonita Legend Wells in South Saskatchewan Observation Well Location Kilometers

6 2. UNDERSTAND THE DROUGHT Drought Vertical Scale Drought Non-drought Non-drought Storage of Water Horizontal Flux of Water

7 3. SIMULATE AND PREDICT THE Global Climate model DROUGHT NWP Model AGCM3 200 km Global Reanalysis GEM 15 km Regional Climate Model CRCM4 45 km Cloud-Resolving Model GEM-LAM 2.5 km Forcings and Initial conditions Process Parameterizations LDAS data flow LDAS Land Surface Hydrology Models CLASS, WATCLASS / MESH 15 km CPM, CRHM 1 km Hydrological Process Models Regional Analysis & obs (for LDAS)

8 Soil Moisture and Drought Agricultural Drought based on soil moisture Atmospheric feedbacks from evaporation and sensible heat controlled by soil moisture Hydrological flows strongly influenced by soil moisture in drought.

9 Hydrological Drought and Soil Evaporation control Moisture Antecedent conditions for runoff generation Unfrozen soils some effect on streamflow generation from heavy rainfall, but not extreme rainfall or snowmelt (upper layers) Frozen soils unsaturated frozen soil moisture content (top 40 cm) can have a strong effect on runoff generation from snowmelt

10 Infiltration into Frozen Soils Snowmelt Water Unlimited Infiltration Limited Infiltration Restricted Infiltration INF = ( 1 θ ) SWE p or Parametric Equation Soils Runoff References: Granger et al., Gray et al., Zhao & Gray

11 Snowmelt Runoff over Frozen Soils Semi-arid SW Saskatchewan Soil moisture is FALL soil moisture Snowmelt runoff is Spring Physically based Infiltration equations (Zhao & Gray, 1999) Cold Regions Hydrological Model

12 Evaporation and Soil Moisture Water vapour flux to the atmosphere from Soil Open Water Vegetation Interception water/snow Stomatal release Snow/ice Precipitation (? depends on how defined) Phase change and transport provides coupling of atmosphere, land surface and sub-surface surface water and energy balances

13 Drought, Soil Moisture & Evaporation Should be Easy! If R = 0, then P = E Not that easy.. E = P - S S This is when sub-surface surface coupling becomes critical to the atmosphere Storage is dynamic during drought. Decreasing surface area of open water, increased root depths, increased depth to water table Seasonality most runoff is from snowmelt (snowfall), most evaporation is from rainfall + snowmelt Precipitation or melt at times of low evaporative energy goes into storage (including soil moisture) or runoff Episodic Events runoff removes water before it can infiltrate and form storage for evaporation. Snowmelt over frozen soil Intense rainfall rates (convective storms).

14 Drought Simulation CRHM: Cold Regions Hydrological Model Rainfall Evaporation Infiltration Interception/Ponding Recharge Zone Soil Surface Runoff Sub-surface Runoff Groundwater Groundwater Flow

15 Change in Resistances to Evaporation during Prairie Soil Moisture Depletion ra (s m -1 ) May 31-May Aerodynamic and Canopy Resistances 5-Jun 22-Jun 27-Jun 2-Jul 14-Jul 26-Jul Date Aerodynamic canopy 7-Aug 17-Aug 23-Aug 28-Aug 4-Sep 9-Sep rc (s m -1 )

16 Page 1 of The Cold Regions Hydrological Model Platform 2006 C:\CRHM\Bad_DLL_7374_pasture.prj cum_soil_runoff(1) cumhru_rain(1) hru_cum_actet(1) soil_moist(1) (mm) P>E R > 0 S little change Energy control on evaporation No Drought /05/ /06/ /06/ /07/ /07/ /08/ /08/1974

17 Page 1 of The Cold Regions Hydrological Model Platform 2006 C:\CRHM\Bad_DLL_7374_pasture.prj cum_soil_runoff(1) cumhru_rain(1) hru_cum_actet(1) soil_moist(1) (mm) P/3 T + 3 o C R = 0 E > P S declines Plant, roots and soil moisture Become important 60 Early Drought /05/ /06/ /06/ /07/ /07/ /08/ /08/1974

18 Page 1 of The Cold Regions Hydrological Model Platform 2006 C:\CRHM\Bad_DLL_7374_pasture.prj cum_soil_runoff(1) cumhru_rain(1) hru_cum_actet(1) soil_moist(1) (mm) P/3 T + 3 o C Si/4 R = 0 E P S depleted Soil moisture critical and limiting 60 Full Drought /05/ /06/ /06/ /07/ /07/ /08/ /08/1974

19 Synthetic Drought Progression Rainfall 222 mm of water No Drought st Summer 1 st 75 Full Drought 75 Evaporation Storage Change Runoff

20 Lethbridge Ameriflux Site (2001)

21 Lethbridge Ameriflux Site (2001) Soil Moisture Initial = 52 mm Max = 200 mm Rech_initial = 13 mm Rech_max = 50 mm Obs G-D P-M BT

22 Lethbridge Ameriflux Site (2001) Soil Moisture Initial = 150 mm Max = 200 mm Rech_initial = 13 mm Rech_max = 50 mm G-D P-M BT Obs

23 DRI Evaporation Workshop Intensive: 19 papers and an open discussion in Saskatoon on 17 May 2007 Presenters identified soil moisture as the greatest unknown in estimating evaporation during drought. Soil moisture essentially controls evaporation during drought. Unknown because Not measured Not modelled well Not appropriately coupled to evaporation models (e.g. depth of rooting zone exceeds model soil depth ) Not linked well to groundwater

24 Evaporation Workshop Summary

25 Presentation Summary I Overview, Measuring and Understanding Need for improved observed data to calculate and bound evaporation (forcing variables, state variables, parameters). Need for new data assimilation (earth observation) to permit more confident evaporation estimation Drought indices may not capture drought evaporation well Need to improve turbulent transfer formulations to account for surface coupling, heterogeneity, advection, snow surfaces Need for better links between evaporation estimation methods and the true soil/ground water storage that is available for evaporation (roots, phenology,, ecosystem water management).

26 Modelling Evaporation Presentation Summary II Resistance networks vs. mosaic approach? Need to improve plant phenology,, root uptake, soil moisture representation. Variety of models available for evaporation. What is best application of the various strategies? Is a coordinated modelling strategy desirable? Possibility of using hydrological/agricultural models to model drought evaporation, concern on what information from streamflow can add during drought when contributing areas are small Model parameterizations Need to address changing landscape structure drying wetlands/lakes, changing root zone, changing land use. Snow redistribution modelling ready for LSS, hydrological models Satellite data assimilation useful way to set parameters and provide inputs (surface temperature, radiation) Feedbacks to atmosphere from evaporation can be important in convection Coupled land surface hydrology models as drought indices (MESH, VIC, VSMB, CRHM, PAM2, EALCO)

27 Discussion Questions/Answers What are the requirements for data and what is the availability of data for calculating evaporation? We need a soil moisture observation network.. Are current evaporation estimation techniques suitable for calculating evaporation (for atmosphere, soil, water resources) No. Problem with short term estimates, problem with soil moisture link via continuity and resistances How might we better estimate evaporation in drought and use estimates to assess drought severity Evaporation estimates in drought are completely controlled by moisture storage and this involves deep soil moisture and groundwater as a continuum How might the hydrometeorological community reduce uncertainty and improve accuracy of evaporation estimates in atmospheric, agricultural and hydrological models? WHAT CAN DRI CONTRIBUTE TO THIS? Prairie parallel to BERMS observational grid with model runs, algorithm testing, remote sensing, tests of data assimilation

28 Workshop Summary What can DRI do? Show how to use available data (surface obs, soil moisture, earth observation, model outputs) ) for calculating evaporation Suggest improvements to evaporation calculation routines Show how evaporation can be used in drought indices

29 DRI Soil Moisture Interests Need to characterize soil moisture spatially and temporally for the recent drought (lack of data!!) Need to understand how soil moisture storage interacts with drought evolution, including feedbacks to the atmosphere. Need to model soil moisture storage and surface interactions in drought accurately in order to better predict drought, water supply, evaporation and atmospheric feedbacks