1. What affects SiB2 runoff? TANG QIUHONG OKI/KANAE LAB. MEETING Univ. of Tokyo 2006/01/30

2. Objective  To make a better runoff and discharge simulation with SiB2 in arid environment.  Requires data on Forcing data for SiB2 Observed discharge to check the SiB2 output

3. Runoff Calculation of Current SiB2

4. Runoff components Roff1: 57%Roff2: 3% Roff3: 34%Roff4: 6% Yellow River basin, Averaged

5. What makes the Roff1? Yellow River basin, One Grid Left: Canopy interception loss (j m 2 ) Right: Ground interception loss For the running time from 94-1-1 to 94-7-3 : Precipitation = 228 mm ; NET E cg = E c (32.6) + E g (0.96) = 33.5 mm Ec = 124.8 - 92.3; condensation is 92.3 mm Eg = 2.82 - 1.85; condensation is 1.85 mm Condensation ( 92.3+1.85= 94.1 mm ) is too large.

6. Revision of SiB2 condensation Limit condensation, and change SH (Sensible heat) to balance energy.

7. After Revision (1) Roff1: 1%Roff2: 9% Roff3: 79%Roff4: 11% Roff1: 57%Roff2: 3% Roff3: 34%Roff4: 6% OLD NEW Yellow River basin, Averaged Yellow River basin, Huayuankou Station D obv = 1088 m 3 /s D new = 747 (-31%) D old = 2225 (104%) D obv = 1088 m 3 /s D new = 747 (-31%) D old = 2225 (104%)

8. After Revision (2) Yellow River basin, Tangnaihai Station Yellow River basin, Zhangjiashan Station D obv = 644 m 3 /s D new = 111 (-83%) D obv = 644 m 3 /s D new = 111 (-83%) D obv = 46 m 3 /s D new = 43 (-8%) D obv = 46 m 3 /s D new = 43 (-8%) No baseflow No surface runoff

9. Conclusion on SiB2 Runoff (1)  SiB2 generates too large condensation and get a ‘error’ runoff.  Limiting condensation can improve much of the runoff and discharge simulation.  But the model gives little surface runoff. the model underestimates runoff. Base flow can not be simulated. Still problems exist

10. Counter the ‘problems’ in SiB2 Richard Equation

11. Surface runoff Infiltration capacity Surface runoff Infiltration Surface runoff Infiltration Infiltration capacity Subgrid variability of precipitation

12. Base flow Flow over a sloping bed Target: To get a ‘steady’ base flow Soil parameters: FAO soil components Cosby et al parameters Slope θ: FAO soil map slope (S s ) θ = α S s

13. Discharge at stations (1982-2000) Time resolution: daily Discharge at stations (1982-2000) Time resolution: daily

14. Discharge at stations (1982-2000) Time resolution: monthly Discharge at stations (1982-2000) Time resolution: monthly

15. Discharge at stations (1982-2000) Time resolution: monthly 1982-2000 averaged value Discharge at stations (1982-2000) Time resolution: monthly 1982-2000 averaged value

16. Balance check (for information) Radl – raul +rans =radt Radt - raet - raht - rast = BALE Radl – raul +rans =radt Radt - raet - raht - rast = BALE Prec -ET + IRR - Roff -DSiB = BAL IRR = 0.

17. Conclusions on Runoff Calculation  The calculated runoff is much decided on the runoff generating mechanism in the hydrological model. Groundwater is required to simulate the base flow.  Subgrid heterogeneity is very important to runoff calculation. Precipitation heterogeneity will affect the runoff calculation.

18. Study area map 17 YONGNING 18 GUYUAN 19 HUANXIAN 17 YONGNING 18 GUYUAN 19 HUANXIAN 20 TONGWEI 21 XIFENGZH 31 TIANSHUI 32 LUSHI 20 TONGWEI 21 XIFENGZH 31 TIANSHUI 32 LUSHI Soil station

19. Soil water depth in top 2cm soil (cm) Time resolution: daily Soil water depth in top 2cm soil (cm) Time resolution: daily

20. Soil water depth in top 1m soil (cm) Time resolution: daily Soil water depth in top 1m soil (cm) Time resolution: daily

21. Soil water depth in top 2cm soil (cm) Time resolution: monthly Soil water depth in top 2cm soil (cm) Time resolution: monthly

22. Soil water depth in top 1m soil (cm) Time resolution: monthly Soil water depth in top 1m soil (cm) Time resolution: monthly

23. Soil water depth in top 2cm soil (cm) Time resolution: monthly 1982-1993 averaged value Soil water depth in top 2cm soil (cm) Time resolution: monthly 1982-1993 averaged value

24. Soil water depth in top 1m soil (cm) Time resolution: monthly 1982-1993 averaged value Soil water depth in top 1m soil (cm) Time resolution: monthly 1982-1993 averaged value

25. Conclusions on soil moisture  Top 2cm soil moisture is relatively well reproduced.  Simulated 1m soil moisture variation is smaller than the observation.  The simulated soil water content (absolute water content) is much decided by the soil parameters.  The station observations may not represent the averaged states of soil moisture.  Subgrid heterogeneity of soil parameters should be considered.

26. Future plan  Subgrid heterogeneity of soil parameters (e.g. K s, porosity, etc.)  Irrigation water withdrawals prediction.

27. Thank you for your attention!