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Simulaciones del ciclo hidrológico en la Península Ibérica con WRF: importancia del reciclaje de agua en la precipitación. Alexandre Rios Entenza, Lucía.

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Presentation on theme: "Simulaciones del ciclo hidrológico en la Península Ibérica con WRF: importancia del reciclaje de agua en la precipitación. Alexandre Rios Entenza, Lucía."— Presentation transcript:

1 Simulaciones del ciclo hidrológico en la Península Ibérica con WRF: importancia del reciclaje de agua en la precipitación. Alexandre Rios Entenza, Lucía Gestal Souto, Gonzalo Miguez-Macho Grupo de Física Non-Lineal Universidade de Santiago de Compostela

2 Outline 1.Explore the link between evapotranspiration and precipitation in the Iberian Peninsula: estimate importance of recycling 2.Evapotranspiration, soil moisture and the water table 3.Calculation of the water table depth for the Iberian Peninsula 4.Conclusions and future work

3 1. LINK BETWEEN EVAPOTRANSPIRATION AND PRECIPITATION: RECYCLING RATIO Question: how much of the precipitation amount falling on a region is actually water originating from the surface in the same region by evapotranspiration? Calculate the recycling ratio (a good measure of the control that local ET fluxes exert on precipitation)

4 Water budget : Balance equation Change in precipitable water Evapotranspiration Precipitation Moisture convergence

5 - RECYCLING RATIO Method 1, using two experiments Control simulation Experiment Method 2, with just one experiment Well mixed atmosphere (based on Trenberth, 1999) Assume that the ratio between the amount of precip. originating from ET and from MC is the same as the ratio between ET and MC themselves (eliminate precipitated water, no infiltration, no feedback)

6 EXPERIMENTAL SETUP: -WRFV model -Nested grid of 1500 km x 1500 km covering the Iberian Península -5 km horizontal resolution -Parent grid (20 km res.) using spectral nudging. -We assume convection is resolved in the nested domain (convective parameterization is turned off).

7 EXPERIMENTS: Large amount of convective precipitation Very wet month with record rainfall in some locations After a very dry winter In the growing season Period: May 2008 Cut-off low around or over the Iberian Peninsula most of the month Monthly mean moisture flux at low levels Two simulations with initial and boundary conditions from GFS: Control Experiment: no feedback between ET and precipitation (precipitated water is eliminated)

8 - Comparison to satellite data (TRMM) RESULTS Even after 23 days, spectral nudging keeps the large scales close to GFS

9 Recycling ratio for the whole Iberian Península; Control Experiment (no infiltration) Difference in total precip (control- experiment)

10 Northwest North Plateau South Plateau West Est Northeast Center High resolution: there are many points in all boxes

11 Control simulationExperiment Reduced precipitation when we suppress infiltration

12 12Z 21 What is the role of water recycling on convective precipitation regimes? Large scale moisture convergence (MC) triggers precipitation (P); evapotranspiration (ET) sustains precipitation after moisture convergence ceases MC P ET Ppw 5 days: May 2008

13 2. EVAPOTRANSPIRATION, SOIL MOISTURE AND THE WATER TABLE Equilibrium soil water profile above a water table at four depths (1, 2, 5, and 10m) for three typical soil types. The water table acts as a lower boundary condition for the unsaturated soil Clay LoamSilt LoamSandy Loam Water table at 10m 5m 2m 1m 10m 5m 2m 1m 5m 2m 1m 10m a) From groundwater to soil moisture:

14 The water table evolves slowly primarily a sink of water source of water for the unsaturated soil A shallow water table increases persistence of root zone soil moisture Beginning of summer End of summer Warm season off-line simulation for North América with LEAF-HYDRO (includes water table dynamics) Flux of water across the water table

15 In a semiarid climate like Arizona, wetter soils in the wtd experiment lead consistently to more ET and more precipitation In Texas, soil moisture has still an important control on ET and ET on precipitation and therefore the impact of the water table is still notable. In Kansas, remote transport of moisture from other continental areas make the response more complicated. A shallower water table still leads in general to more ET, but not always to more precipitation. In the humid climate all year round of Indiana, ET is mostly controlled by atmospheric demand. The presence of the water table still produces a wetter soil, but this does not have a large impact on ET (the soil is sufficiently wet without the water table as well). ET has little control on precipitation, which depends more on large scale moisture convergence Evapotranspiration (blue bars) Precipitation (green bars down) Moisture converge (red curve) Precip.water difference (black curve)

16 b) From soil moisture to evapotranspiration and precipitation Soil moisture control on evapotranspiration and precipitation is largest in semi-arid (water limited) regions. In humid climates, evapotranspiration is more controled by atmospheric demand, and large scale convergence controls precipitation -The Iberian Peninsula is largely a semi-arid region and ET has an important role on precipitation. Groundwater (the water table) can potentially have an important impact on soil moisture dynamics and evapotranspiration, and therefore on precipitation and climate. Question: what does the water table look like?

17 We use a groundwater model to calculate the equilibrium water table, or the position where climatological recharge balances the lateral flow R Qn R Qr R R msl Dry climate Humid climate We use an estimation of recharge from ECMWF HTESSEL model Resolution is 30’’ (~1km)

18 Lateral flow w i,j Q1Q1 Q2Q2 Q3Q3 Q4Q4 Q5Q5 Q6Q6 Q7Q7 Q8Q8 Plan view h i,j Mean sea level SgSg Q8Q8 Q4Q4 Rech. Cell ij Cross section view width of flow cross section Transmisivity Head difference divided by distance conductivity (Darcy’s law)

19 - Equilibrium water table depth (EWTD, m) for the Iberian Peninsula The WATER TABLE is shallow in many areas, and precisely in those were we found a highest recycling ratio

20 Mean WTD from all available times at observation points EWTD from model at observation points Well known wetland areas don’t show up clearly in the observations (problem with obs: agricultural pumping)

21 Many observation time series have marked trends of decreasing water table depth due to massive agricultural use of groundwater Example of observations in the La Mancha húmeda area

22 5. CONCLUSIONS -We find important recycling ratios during the springtime, where precipitation is especially important for plants and agriculture. -The highest recycling ratios are located in some of the dryest regions, which suggest that recycling and evapotranspiration play a key role in precipitation and climate there. -The water table is shallow in a significant area of the Iberian Peninsula, even in semiarid regions. We expect in these areas that groundwater affects soil moisture dynamics and evapotranspiration and therefore precipitation and climate. Future work: run coupled hydro simulations for longer periods to establish the role of groundwater on soil moisture dynamics, ET and precipitation. and the impact of the observed water table depletion on climate

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