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Modifications and Experiments Default CLM2: precipitation occurs over the entire grid cell Interception Scheme: Convective precipitation occurs only (RE Dickinson) Pconv f conv Plarge = 0. fconv = 10% Pl arg e 10 * Pconv Pconv = 0. fconv = 100% Simplified Topmodel : more closely following TOPMODEL but improved schemes for water table, saturated area, surface runoff and baseflow; super-saturated water recharged to unsaturated soil layers. Frozen Soil: Relax frozen soil control on hydraulic conductivity ( hsat increased in cold regions) The NCAR CLM2-GSWP2 The CLM2 run with the GSWP2 3-hr forcing data at 1-hr time step (1983-1995) 10-year monthly runoff outputs (1986-1995) Improvement index = 12 ( EXP OBS ) / 2 imon1 12 2 ( Default OBS ) imon1 <1 improvement >1 degradation TOPMODEL vs. CONTROL Degrade Improve Frozen Soil Effects Degrade 0 Improve Runoff over snow-covered areas UNH-GRDC Observed Runoff (mm/day) The NCAR CLM2 simulated Runoff (mm/day) CLM2 – USAF/ETAC observed Snow Depth (m) The simulated runoff in May is much higher than the GRDC observed in North Europe and West Siberia, because the CLM2 produced much more snow than the USAF/ETAC observed Regional Averages (Arctic and Boreal Regions) North Europe (55-70N, 5-60E) West Siberia (50-70N, 60-90E) Model OBS East Siberia (50-70N, 90-140E) North Canada (50-70N, 90-170W) Regional Averages (Tropical Regions) Central America (10-25N, 60-110W) Amazon Basin (10S-0N, 50-70W) Congo (10S-5N, 10-30E) India (10-30N, 70-90E) Regional Averages (Midlatitudes) Western U.S. (30-50N, 110-130W) Central U.S. (30-50N, 90-110W) Eastern U.S. (30-50N, 70-90W) Central Europe (40-55N, 0-40E) Regional Averages (Arid Regions) Sahara+Arabian Peninsula(10-30N, 0-50E) Southern South America (25-60S, 50-80W) South Africa (10-35S, 10-40E) Australia (10-40S, 110-160W) Soil Moisture (mm/day) Surface Runoff (mm/day) Canopy Evaporation (mm/day) Amazon Region The new interception scheme intercepts less water, allowing more water to reach the ground and increase surface runoff instead of increasing soil moisture. The simplified TOPMODEL largely decreases the surface runoff, allowing more water to infiltrate into deeper soil and increase soil moisture. Infiltration and the Water Table • After a storm event, water infiltrates through the unsaturated zone, and recharges the ground water reservoir • This raises the elevation of the water table, increasing the gradient and the flow of ground water away from the recharge point. This results in increased flow at the discharge point • Increased evaporation, or withdrawal by pumping, lowers the water table by increasing the discharge from that reservoir Aquifers • Unconfined Aquifers have an upper boundary defined by the water table • Confined aquifer (Artesian): The upper boundary is a confining layer (Aquitard) – The water level (head) in a well penetrating confined aquifer rises above the level of the confining layer – The surface defined by the water level is the piezometric (or potentiometric) surface, and is not the water table – Some are also flowing artesian wells Water Table Simulations over the Amazon Basin Topographic Index λ Simulations over the Amazon Basin Simulations over the Amazon Basin