Canadian Hydrological Drought: Processes and Modelling John Pomeroy, Robert Armstrong, Kevin Shook, Logan Fang, Tom Brown, Lawrence Martz Centre for Hydrology, University of Saskatchewan, Saskatoon

Prairie Hydrology - Reality Smith Creek, Saskatchewan

Overview OBJECTIVE OBJECTIVE To better understand, describe and model the development of hydrological drought on the Prairies FOCUS – evaluation and drought sensitivity of FOCUS – evaluation and drought sensitivity of Processes Processes Snow Redistribution, Accumulation and Melt Snow Redistribution, Accumulation and Melt Runoff Generation/Wetland Recharge Runoff Generation/Wetland Recharge Areal Evaporation Areal Evaporation Modelling Modelling Prairie Hydrological Modelling – CRHM platform to create physically based hydrological models of soil moisture, evaporation, snow accumulation, small prairie stream runoff and wetland recharge Prairie Hydrological Modelling – CRHM platform to create physically based hydrological models of soil moisture, evaporation, snow accumulation, small prairie stream runoff and wetland recharge

Calculating Prairie Snowmelt Runoff Calculating Prairie Snowmelt Runoff

Spatially distributed blowing snow model Spatially distributed blowing snow model 262,144 grids 262,144 grids On each grid calculation of fluxes based on On each grid calculation of fluxes based on St Denis, Saskatchewan

Spatially Distributed Blowing Snow Accumulation - Feb

Spatially Distributed Blowing Snow Accumulation – End of March

Blowing Snow in Operational Drought Modelling For hydrological and agricultural water balance applications, need landscape type specific calculations, aggregated approach For hydrological and agricultural water balance applications, need landscape type specific calculations, aggregated approach To calculate mass balance for landscape unit (TILE), need inputs from upwind tiles (source to sink) To calculate mass balance for landscape unit (TILE), need inputs from upwind tiles (source to sink) Possible to calculate transport from one tile to another Possible to calculate transport from one tile to another Calculation order based on tile aerodynamic sequence (smooth to rough; high elevation to low elevation). Transport out from one tile is transport in to next tile. Calculation order based on tile aerodynamic sequence (smooth to rough; high elevation to low elevation). Transport out from one tile is transport in to next tile. Important to preserve continuity at multiple scales Important to preserve continuity at multiple scales Fallow Field Stubble Field GrasslandBrushTrees

Spatially Aggregated Blowing Snow Accumulation, 7 tiles

Distributed vs Aggregated Blowing Snow Modelling Areal average SWE from two resolutions of blowing snow model and snow surveys distributed = 111 mm, aggregated = 90 mm, and observed = 97 mm.

Prairie Evaporation Actual Evaporation critical component of drought Actual Evaporation critical component of drought Uncertainty in estimating Evaporation Uncertainty in estimating Evaporation Various theoretical relationships with differing sets of parameters (α, z o, d, vegetation, water), variables (K↓, L↓, u, T, q) and state variables (θ, T s ) Various theoretical relationships with differing sets of parameters (α, z o, d, vegetation, water), variables (K↓, L↓, u, T, q) and state variables (θ, T s ) Highly spatial variability) – Highly spatial variability) – subgrid variability subgrid variability Advection to ponds Advection to ponds Aggregation in LSS. Aggregation in LSS. Tiles Tiles Problem of changing tile area during drought Problem of changing tile area during drought Continuity Continuity All models limit water for evaporation by tracking supply All models limit water for evaporation by tracking supply Prairie plants don ’ t care and send roots to available water (+3 m) Prairie plants don ’ t care and send roots to available water (+3 m)

Field Observation NECESSARY St Denis National Wildlife Area, Saskatchewan

St Denis, SK, summer 2006, dry but no drought 3 physically based methods (Granger GD, Penman-Monteith, Dalton Bulk transfer {LSS-like} compared to best observation sets from eddy correlation. Possible to set soil moisture for resistance and continuity aspects of CRHM from field measurements of soil water (no model calibration).

Lethbridge Ameriflux Site (2001) Entered Drought as summer 2001 Progressed Severe Decline in Soil water content and daily actual evaporation

Modeling evaporation under drought conditions requires soil moisture accounting Influence of canopy resistance term increases as season progresses Uncertainty in reference minimum for resistance – PM, BT Not possible to set physically realistic parameters for Penman-Monteith and Dalton Bulk Transfer resistance schemes, Granger GD method in CRHM performed well in severe drought

Important for hydrology Wetland recharge and dessication Streamflow generation, contributing area for runoff Two eddy correlation systems, 2007, pond and dryland Spatial Variability of Prairie Evaporation

Thermal Image of St. Denis NWA (2007) Taken from an infrared imager from an airplane Island Mixed Grasses Cultivated Pond 90 wetlands Trees Aug 5, 2007;12:12 pm road Provides basis for spatial distribution of net radiation in Granger GD evaporation method

Distributed Daily Evaporation St Denis Distributed: -Outgoing longwave -Outgoing shortwave -Aerodynamic roughness Granger GD Model with “ common ” atmospheric feedback, T, RH,

Spatial Frequency Distribution of Actual Evaporation (one day) wetland dryland mm daily actual evaporation

Cold Regions Hydrological Model Process Modules Developed from research at University of Saskatchewan and EC over several decades Developed from research at University of Saskatchewan and EC over several decades Radiation (slopes, estimation procedures) Radiation (slopes, estimation procedures) Blowing snow (snow transport & sublimation) Blowing snow (snow transport & sublimation) Interception (rain and snow) Interception (rain and snow) Snowmelt (open & forest, advection, energy balance) Snowmelt (open & forest, advection, energy balance) Infiltration (frozen and unfrozen soils) Infiltration (frozen and unfrozen soils) Evaporation (Granger or Penman-Monteith) Evaporation (Granger or Penman-Monteith) Soil moisture balance (with groundwater interaction) Soil moisture balance (with groundwater interaction) Routing (hillslopes, sub-surface and streamflow) Routing (hillslopes, sub-surface and streamflow)

CRHM Use for DRI Hydrological evolution and feedbacks in drought Hydrological evolution and feedbacks in drought Hydrological Drought Indices based on small basin soil moisture, streamflow and wetland levels Hydrological Drought Indices based on small basin soil moisture, streamflow and wetland levels Scaling methodology and process test bed Scaling methodology and process test bed Evaluate prairie land surface parameterisations and aggregation for MESH Evaluate prairie land surface parameterisations and aggregation for MESH Develop prairie hydrology routing for MESH Develop prairie hydrology routing for MESH Provide drought hydrology tool for users Provide drought hydrology tool for users

/05 Drought Impact at St. Denis, cumulative effect on the hydrological processes and wetland water level modelled with CRHM

CRHM Test at Wetland 109, St Denis

CRHM Application to Prairies Apply to two representative types of basins (RB) Apply to two representative types of basins (RB) Well drained small prairie stream Well drained small prairie stream Wetland basin with much surface storage Wetland basin with much surface storage Create prairie drought surface of basin state variables Create prairie drought surface of basin state variables Need standard atmospheric observations or reanalysis data (U,T, RH, Precip) Need standard atmospheric observations or reanalysis data (U,T, RH, Precip) Needs radiation (sparse observations!!!) Needs radiation (sparse observations!!!) Calculates soil moisture, streamflow, water storage, snowpack as state variables Calculates soil moisture, streamflow, water storage, snowpack as state variables

NARR Daily Qsi

NARR => CRHM Simulated Hourly Qsi

Creating Frequency Distributions of Wetlands for Hydrological Modelling of Prairie Wetland Representative Basin Need to have characteristic frequency distribution of wetlands – this changes during drought. Need to have characteristic frequency distribution of wetlands – this changes during drought. Test at St Denis where excellent data exists …… Test at St Denis where excellent data exists …… Simply route water excess along surface topography from one storage area to the next Simply route water excess along surface topography from one storage area to the next

0.1 m water added to DEM

0.3 m water added to DEM

St. Denis Slough Simulation Runoff from spatially-constant precip - spatially-constant Evap. Need spatially variable evaporation

Conclusions Successful physically-based prairie hydrological modelling for small basins using CRHM – no calibration Successful physically-based prairie hydrological modelling for small basins using CRHM – no calibration Spatial scale for blowing snow accumulation and spring runoff calculation determined – tiled approach adequate Spatial scale for blowing snow accumulation and spring runoff calculation determined – tiled approach adequate Suppression of blowing snow transport and enhancement of frozen soil infiltration responsible for much of wetland desiccation in drought Suppression of blowing snow transport and enhancement of frozen soil infiltration responsible for much of wetland desiccation in drought Evaluation of evaporation models and observations suggests that soil moisture should be a product rather than a driver of evaporation calculations. Possible to distribute Granger method. Evaluation of evaporation models and observations suggests that soil moisture should be a product rather than a driver of evaporation calculations. Possible to distribute Granger method. Spatial distribution of evaporation, pond storage and runoff provides basis for upscaling atmospheric feedbacks and calculating hydrology in drought. Spatial distribution of evaporation, pond storage and runoff provides basis for upscaling atmospheric feedbacks and calculating hydrology in drought. CRHM ready for application to develop Prairie-wide hydrological drought products, Representative Basin soil water, runoff, water storage CRHM ready for application to develop Prairie-wide hydrological drought products, Representative Basin soil water, runoff, water storage