Jeffrey Richey & Colleague University of Washington SEA-BASINS

Transcription

1 Does Deforestation affect River Flows across the Mekong Basin? What Controls Water Flows across the Mekong Basin: (Geology), Climate, Landcover (Change), Engineering, Jeffrey Richey & Colleague University of Washington SEA-BASINS

2 We have 2 OBJECTIVES: Mine: Evaluate the Issue of Mekong Flows - Measured truth - Modeling as analytical tool - Details of discharge regime: Climate influences - Engineering - Landcover change My friend s sub-plot: To remind us that the integrated approach used is more than just hydrology modeling, is imminently transportable to other regions, the sheer act of building such an analysis promotes interdisciplinary cooperation, and there are very useful stakeholder/policy applications..

3 Mae Chaem Basin, NW Thailand (as proxy for feeder to Mekong) 55 5 % croplands Observed discharge, m3/s 19.9 Pearson r = Simulated 19.1 discharge, m3/s /94 1/94 5/95 11/95 5/96 11/96 5/97 11/97 5/98 11/98 5/99 11/99 5/ 11/

4 Yunnan >461 m <3 m CS Chiang Saen Luang Prabang Vientiane Mukdahan Pakse LP MN BHH MM Vt NP BC Mk Ys RS Ub BKD Pk Stung Treng Phnom Penh ST Tonle Sap PP

5 *How does land use intensification affect watershed functions in large-scale drainage basins (high flow, low flow)? Would switching landcover back to forest change flow regimes? *How does total water yield depend on the distribution of rainfall and portioning between hydrologic processes, under historical and current conditions? *How are the temporal dynamics of high and low flows of rivers influenced by spatial scale? *How are Far field effects on people living downstream linked to changes in total and seasonal water yield?

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7 3 2 Chiang Saen LONG-TERM DISCHARGE: THE TRUTH Mekong Mainstem Luang Prabang Vientiane Mukdahan Stung Treng

8 Ubon LONG-TERM DISCHARGE: THE TRUTH Mun-Chi (NE Thailand) Yasothon Rasai Salai Ban Chot

9 To deconvolve the signal, we need suitable tools.. MEKONG These geospatially-explicit VIC (Variable Infiltration process-based Capacity) models are an Meso/Macroscale Landscape/Hydrologic Model exciting new tool, as + Reservors representation + Irrigation of space and dynamics, from tectonics to a local (Daily, rainstorm. 1-1 km) This allows exploration, but the answer is grounded in the assumptions.. Should be thought of as intelligent interpolators of diffuse data Today is Version 3, advanced as (solid) basis for discussion of details. not a priori the definitive answer

10 Virtual Scaled Basin The Mekong (and 1km (or 1 m).

11 Digital Elevation Model & River Network Tonle Sap 1-km GTOPO3 DEM 1-km resolution, using upscaling

12 SOILS From USDA texture classes to soil parameters saturated hydraulic conductivity (Ks), porosity (qs), field capacity (qc), wilting point (qw), and parameter n in the Brooks-Corey equation for unsaturated conductivity Top layer (-1 cm) Deeper layer (1-1 cm)

13 VEGETATION GETTING IT RIGHT MODIS/ OGE Rice OGE UMD MSU MODIS/ OGE Rice GLC/SE Asia GLC/Asia

14 VEGETATION CLASSES.of interest to many, for multiple purposes Minimum stomatal resistance, RGL, and solar radiation attenuation Vegetation height, displacement height, roughness length, and architectural resistance Leaf Area Index, albedo Maximum rooting depth, and distribution of root mass with depth Wind height and wind attenuation

15 Surface Climatology Wind speed data: interpolated from the NCEP-NCAR Reanalysis data set; Minimum and maximum daily temperature and wind speed value, Surface Summary of Day Data (SoD) records from the National Climate Data Center (NCDC); interpolated

16 * Approximate from DEM Observed vs Predicted River Flow Issues of calibration, validation

17 MEKONG DISCHARGE (m 3 /s; monthly) OBSERVED ( ) VIC-COMPUTED ( ) 12 Chiang Saen Phnom Penh Luang Prabang Stung Treng 2 Vientiane Pakse 28 Mukdahan Nakhon Phanom

18 8 6 4 Ban Chot MEKONG TRIBS DISCHARGE (m 3 /s; monthly) OBSERVED ( ) VIC-COMPUTED( ) 28 Muong Ngoy Rasi Salai Ban Hin Heup Ubon Yasothon Inputs Tonle Sap 6

19 Diagnostic Landscape/Hydrology Processes Average annual simulated runoff ratio

20 Average monthly soil moisture saturation in in the calibrated simulation (farmers, flood prediction)

21 Functional Relations; e.g. Vientiane 4 3 Precipitation Soil Moisture) Discharge 8 4

22 Soil Moisture Antecedent: the 2 Flood Chiang Saen Ubon

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24 Vientiane DISCHARGE ANOMALIES (mo) Stueng Treng Ubon

25 REGIONAL CLIMATE PROXIES Indian Ocean Sea Surface Temperature Pacific Decadal Oscillation Southern Oscillation Index

26 Composite SLP anomaly maps for 12 highest & lowest Stueng annual flow years Jan-June (yr) Jul-Dec (yr) Highest Lowest Contour/shading interval =.5mb

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28 EFFECT OF DAMS ON FLOW 16 Ubol Ratana % (Σ=-14%) Input Output 5 Nam Ngum(Σ=-15%) % 8% 4% 4% 2% -2% % % -1%

29 Irrigation (esp NE Thailand) 12% 1% 8% Rasi Salai 6% 4% 2% % Ubon Yasothon J F M A M J J A S O N D Near Udonthani

30 Land Cover Scenarios Permanent v Swidden Agriculture (of different fallow periods) Scenario Ω f (yr) Percentage of current forest (and classes 21 and 22) replaced by these land cover classes 23 9 Total (agriculture) (6-15 years in fallow) 9A (1-5 years in fallow) 9B (16-3 years in fallow) Percentage of current permanent agriculture (class 23) replaced by forest (forest class 5; except for China, where forest class 28 is introduced) Permanent agriculture scenarios: Sc.1 1% deforestation - - 1% % - Sc.2 1% deforestation - - 1% % - Sc.3 1% afforestation % Sc.4 1% afforestation % Swidden agriculture scenarios: Sc.5 Increased Ω 5 Ω =131,245 km 2 Sc.6 Sc.7 Increased Ω but long fallow period No swidden agriculture 5 Ω =131,245 km 2 5 5/6 Ω =21,874 km 2 =11.5% 3 5/31 Ω =4,234 km 2 =2.2% 25/6 Ω =19,37 1 km 2 =57.4% 25/31 Ω =21,169 km 2 =11.1% - - 5/31 Ω =42,337 km 2 =22.2% 75/31 Ω =63,56 km 2 =33.3% 68.9% 68.9%? % - -

31 Land Cover Scenarios (Tributaries) 15% 1% 5% % -5% -1% -15% -2% 1% 5% % -5% -1% -15% Ban Hin Heup Muong Ngoy J F M A M J J A S O N D 1% def. 1% def. 1% aff. 1% aff. Fallow=5 yr Fallow=3 yr No swidd. ag.

32 Land Cover 1% : MEKONG BASIN 2% 15% 1% Deforestation 2% 15% 1% Deforestation 1% 1% 5% 5% % % J F M A M J J A S O N D J F M A M J J A S O N D % -2% -4% -6% % -5% -1% -8% -1% 1% Afforestation -15% -2% 1% Afforest Ban Hin Heup Muong Ngoy ` Ban Chot Rasi Salai Yasothon Ubon Chiang Saen Luang Prabang Vientiane Nakhon Phanom Mukdahan Pakse Stung Treng

33 Obj. 1. Are upstream changes detectable as farfield affects on water yield even in a very big basin? Depends quantitatively!- on relative magnitude, in a dynamic (in)balance: Transition forest to agriculture Irrigation Dams Climate Obj. 2. Applications of VSB Construct as a Tool Scenario & Dynamics Analyses: Past, Present, Future Now-casting Drought and flood forecasting (especially if coupled to climate model) Elsewhere very much! Mekong River Commission Secretariat, Vientiane