Improvement of surface layer forecasts by modifying the hydrological cycle in NOAH LSM used in GRAPES_Meso model

Transcription

1 Improvement of surface layer forecasts by modifying the hydrological cycle in NOAH LSM used in GRAPES_Meso model Dr. Dehui CHEN and Dr. Lili WANG National Meteorological Center, China Meteorological Administration, China for EMS2012, Sep. 12, 2012, Lodz, Poland

2 Outline 1 Motivation 2 Modification of hydrological cycle in NOAH LSM 3 Simulations with GRAPES_Meso using the improved NOAH LSM 4 Conclusion and Future plan 2

3 Outline 1 Motivation 2 Modification of hydrological cycle in NOAH LSM 3 Simulations with GRAPES_Meso using the improved NOAH LSM 4 Conclusion and Future plan 3

4 1 Motivation NOAH LSM is one of the most advanced LSM in the literature and widely used in both weather and climate modeling. Since 1990s, NOAH LSM has been operationally used in the NWP systems of NOAA/NCEP/EMC (refs. Ek, 2003; Chen et al., 1996) The main features of NOAH LSM can be illustrated the following figure (refs. Chen et al 1996; Schaake et al., 1996; Koren et al 1999; Ek et al., 2003) 4

5 (1) linearized (non-iterative) surface energy budget (2) intercepted canopy water (3) bare soil evaporation (4) vegetation-reduced soil thermal conductivity (5) multiple soil layers, with soil moisture diffusion and soil heat conduction equation for different soil textures (6) frozen soil processes (7) single-layer snowpack, snow density, max snow albedo (8) patchy snow cover affect on surface fluxes (refs. Chen et al 1996, Schaake et al 1996,Koren et al 1999, Ek et al 2003) Noah land-surface model 5

6 Hydrological cycling in Noah LSM Noah-LSM hydrological cycling by a SWB (Simple Water Balance): where Rs: surface runoff; P: net precipitation; E: evapotranspiration; Imax: maximal Infiltration to the ground with I max ( P E) P D d R x P E s I max 1 1 exp kdt exp kdt t t Two main disadvantages in Noah LSM: (1) The inhomogeneity of amount of precipitation and area of runoff yield within a coarser grid box (0.15 o 0.15 o for this case) is not considered in NOAH LSM; (2) There is no flow routing between the grid box during integration.

7 Runoff depths simulated by GRAPES_Meso with Noah LSM: 0-6h 6-12h 12-18h 18-24h Runoff depth(mm) (initial time: Jul.15 th, 2010, 8:00 BJT) Nearly no changes of the runoff depths during the integration time 7

8 Objective of Research (1) To improve hydrological cycling in Noah LSM by 1) Modification of the SWB (Simple Water Balance) process; 2) Addition of flow routing to complete the hydrological cycling; (2) To investigate their impacts on surface layer forecasts with GRAPES_Meso. GRAPES: is short form of Global/Regional Assimilation and PrEdiction System for the new generation of NWP system of CMA (refs. Chen et al., 2003, 2008; Xue and Chen, 2008) 8

9 Outline 1 Motivation 2 Modification of hydrological cycle in NOAH LSM 3 Simulations with GRAPES_Meso using the improved NOAH LSM 4 Conclusion and Future plan 9

10 For improving Hydrological Cycling in Noah LSM: (1) to use Zhao-84 scheme with soil water storage variations; (ref. Zhao,1984); (2) to introduce MC (Muskingum-Cunge) method for flow routing to descript surface flow, interflow and groundflow between the grid box; (ref. Bates, 2000). 10

11 Soil Water Storage Curve in Zhao-84 scheme Variation of runoff yield depending on : Runoff yield in part of grid box: Runoff yield in whole grid box: where f is area of runoff yield(km 2 ); F is area of grid box(km 2 );W is water content (mm) at a point; WMM is max water content (mm) at a point; B is index of soil water storage curve; W0 is initial water content (mm); WM is average of max water content (mm); Rs is surface runoff (mm); A is specified by: Root Zone Unsaturated Zone Saturated Zone Bedrock Soil Water Storage Curve Stream Water Table 11

12 Improvement of runoff-depth simulation with NOAH LSM used in GRAPES_Meso: 0-6h 6-12h with new scheme 0-6h 6-12h with old SWB Runoff depth(mm) (initial time: 8:00 Jul.15th.2010, BJT) 12

13 Improvement of of runoff-depth simulation with NOAH LSM used in GRAPES_Meso : 12-18h 18-24h with new scheme 12-18h 18-24h with old SWB Runoff depth(mm) (initial time: 8:00 Jul.15th.2010, BJT) 13

14 t 1 t t 1 t i 1 1 i 2 i 3 i Method to determine flow routing: As shown, the flow at the grid a, b, and c can all flow into grid d. The outflows is Qa, Qb, Qc respectively. Q a is obtained by the Muskingum-Cunge s flow routing method (ref. Bates, 2000) : ' t 1 t t 1 ' t Qai 1 C1Q ai C2Qai C3Qai 1 Q C Q C Q C Q 1 Same as Q b and Q c.

15 The Yellow River and The Yangtze River basins (after filled DEM) 15

16 Outline 1 Motivation 2 Modification of hydrological cycle in NOAH LSM 3 Simulations with GRAPES_Meso using the improved NOAH LSM 4 Conclusion and Future plan 16

17 Experiment(1) design: Impacts on surface layer forecasts GRAPES_Meso: Initial and bi-lateral conditions: NCEP global operational GFS with 1ºX1ºresolution H. resolution: 0.15ºX15º V. levels: 26 levels Forecast: 72hrs Domain: (1) 33º-42ºN, 110º-122ºE Period: case studies (initial Time: , 00UTC) NOAH LSM: SWB hyd. cycle vs modified Hyd. cycle 17

18 Simulations with old and new H.C. scheme 0-6h 0-6h Soil moisture with old with old 0-6h 0-6h Precipitation with new with new

19 Simulations with old and new H.C. scheme 6-12h 6-12h Soil moisture with old with old 6-12h 6-12h Precipitation with new with new

20 Simulations with old and new H.C. scheme 12-18h 12-18h Soil moisture with old with old 12-18h 12-18h Precipitation with new with new

21 Simulations with old and new H.C. scheme 18-24h 18-24h Soil moisture with old 18-24h 18-24h with old Precipitation with new with new

22 Simulations with old and new H.C. scheme 6-12h Soil moisture with old 6-12h with new

23 Simulations with old and new H.C. scheme 18-24h Soil moisture 18-24h with old with new

24 Simulations with old and new H.C. scheme soil moisture surface evaporation soil temperature surface temperature

25 Simulations with old and new H.C. scheme T2m ground heat flux surface latent heat flux surface sensible heat flux

26 Simulations with old and new H.C. scheme cloud cover at 850hpa cloud water 850hpa water vapor at 850hpa few changes, except to qc

27 Precipitation forecasts vs Observation new old 48hrs accumulated precipitations of two runs: quite similar, except to location of precipitation zones. Obs. Initial time: UTC

28 Handan station Patou stations obs. with new with SWB Wuyi station Pingxiang station

29 Experiment(2) design: Impacts on hydrological forecasts GRAPES_Meso: Initial and bi-lateral conditions: NCEP global operational GFS with 1ºX1ºresolution H. resolution: 0.15ºX15º V. levels: 26 levels Forecast: 48hrs Domain: (1) 30º-37ºN, 111º-120ºE Period: case studies ( , 00UTC) NOAH LSM: SWB hyd. cycle vs modified Hyd. cycle 30

30 Experiment (2) Old NOAH LSM 24-30h 24-30h Runoff Depth 24-30h 24-30h Precipitation Modified NOAH 31

31 Experiment (2) Old NOAH LSM 30-36h 30-36h Runoff Depth 30-36h 30-36h Precipitation Modified NOAH 32

32 Experiment (2) Old NOAH LSM 36-42h 36-42h Runoff Depth 36-42h 36-42h Precipitation Modified NOAH 33

33 Experiment (2) Old NOAH LSM 42-48h 42-48h Runoff Depth 42-48h 42-48h Precipitation Modified NOAH 34

34 Experiment (2) GRAPES_Meso with modified LSM GRAPES_Meso with old LSM Wangjiaba Station 08:00 15 th - 08:00 18 th Jul.2010,BJT 35

35 Experiment(3) design: Impacts in a GRAPES_Meso: Initial and bi-lateral conditions: NCEP global operational GFS with 1ºX1ºresolution H. resolution: 0.15ºX15º V. levels: 26 levels Forecast: 48hrs longer period Domain: (2) 15º-64.5ºN,70º-145.3ºE Period: 9 Aug to 27 Sept, 2008 NOAH LSM: SWB hyd. cycle vs modified Hyd. cycle 36

36 Experiment (3) Station Name Latitude(ºN) Longitude(ºE) Province Basin Nanchong Sichuang Yangtze River Linfen Shanxi Yellow River 37

37 Outline 1 Motivation 2 Modification of hydrological cycle in NOAH LSM 3 Simulations with GRAPES_Meso using the improved NOAH LSM 4 Conclusions and Future plan 38

38 Conclusions The hydrological cycle in NOAH LSM has been successfully modified by (1) using Zhao-84 scheme with soil water storage variations(ref. Zhao,1984), and (2) adding M-C method for flow routing to descript surface flow, interflow and groundflow between the grid box(ref. Bates, 2000) ; Impacts on surface layer forecasts: having more evaporation, more soil moisture, reducing surface temperature; forecasts of soil moisture improved in comparison to observations; Impacts on hydrological forecasts: significantly increasing runoff depth, so improving prediction of discharge of water; 39

39 Future plan Hydrological parameters need to be further optimized in the modified Noah LSM; It is necessary to carry out the off-line tests and more and real-time experiments to verify its performance of both meteorological and hydrological forecasts; It is planning to introduce the modified NOAH LSM to GRAPES_GFS for the experiments of global medium range forecasts. 40

40 for your attention 41