Anthropogenic impacts on the water balance of large river basins

Transcription

1 Anthropogenic impacts on the water balance of large river basins Ingjerd Haddeland, Thomas Skaugen (University of Oslo) Dennis P. Lettenmaier (University of Washington)

2 Outline Background Approach Results Conclusions

3 Introduction Irrigation: 6-7 % of global water withdrawals (Shiklomanov, 1997) ICOLD: >3, large dams 35 % built for irrigation purposes alone Freshwater scarcity: one of the most important environmental issues of the 21st century (UNEP, 1999) Vörösmarty and Sahagian, Bioscience, 2.

4 Irrigated areas

5 Irrigated areas 5 N 4 N 3 N 6 N 12 W 11 W 1 W 9 W 8 W 7 W Percent irrigated areas > <.1 3 E 6 E 9 E 12 E 15 E Irrigated areas, globally: 2.5*1 6 km % of global land area Location of irrigated areas: Asia: 68% America: 16% China, India, USA: 47% 3 N Stefan Siebert, Petra Döll, Sebastian Feick and Jippe Hoogeveen (25), Global map of irrigated areas version 3, Institute of Physical Geography, University of Frankfurt, Germany / Food and Agriculture Organization of the United Nations, Rome, Italy

6 Irrigation: Definitions Irrigation water requirements: Water required in addition to water from precipitation (soil moisture) for optimal plant growth during the growing season (Consumptive) irrigation water use: Water, in addition to water from precipitation, actually used by plants. Is equal to, or less, than irrigation water requirements. Irrigation water deficits: Irrigation water requirements Irrigation water use

7 Reservoirs

8 Reservoirs 5 N 4 N 3 N 12 W 11 W 1 W 9 W 8 W 7 W Percent irrigated areas > <.1 Dam 3 E 6 E 9 E 12 E 15 E Irrigation Flood Fraction of all dams Hydro Fishing Navigation Main purpose of dam Recreation Water supply Unknown 6 N 3 N Irrigation Flood Hydro Fishing Navigation Recreation Water supply Unknown ICOLD, 23. World Register of Dams 23, International Commission on Large Dams (ICOLD), Paris, France.

9 Previous studies 2% of global mean annual runoff can be retained in reservoirs (Vörösmarty et al., Ambio, 1997) Reservoirs alters continental monthly river disharge by up to 34% (Hanasaki et al., Journal of Hydrology, 26) Irrigation water requirements range from 11 km 3 year -1 (Döll and Siebert, Water Resources Research, 22) to 23 km 3 year -1 (Shiklomanov, United Nations, 1997) Irrigation increases latent heat flux by 9.5% over the Indian Peninsaula (derosnay et al., Geophysical Research Letters, 23) Global mean radiative forcing is increased by up to.1 Wm -2, temperatures decreases up to.8k over irrigated areas (Boucher et al., Climate Dynamics, 24)

10 Measurements

11 Objective of this study The effects of irrigation and large reservoirs on the water balance are studied with the objective of obtaining plausible reproductions of observed flows at the outlets of large river basins, with a special emphasis on river basins affected by irrigation. Traditional macroscale models: Simulates naturalized streamflow Model development: Generic reservoir model Irrigation scheme m 3 s ) Columbia J F M A M J J A S O N D Naturalized Observed

12 Variable Infiltration Capacity model

13 Approach Macroscale hydrologic model: VIC Resolution Spatial:.5 degrees Temporal: Daily Input data Precipitation, max/min temperature, wind Land cover data (vegetation, soil properties, topography) Time period: Irrigation scheme VIC. Surface water withdrawals only Reservoir module Routing model Cropland Grasslands Open Shrublands Closed Shrublands Wooded Grasslands Woodland Mixed Cover Deciduous Broadleaf Deciduous Needleleaf Evergreen Broadleaf Evergreen Needleleaf Bare soil/ice Dominant vegetation type Evergreen Needleleaf Evergreen Broadleaf Deciduous Needleleaf Deciduous Broadleaf Mixed Cover Woodland Wooded Grasslands Closed Shrublands Open Shrublands Grasslands Cropland Bare soil/ice Second most dominant vegetation type

14 Irrigation scheme Irrigation starts Irrigation ends Soil moisture Soil moisture Field capacity Wcr 1 Time

15 Irrigation scheme VIETNAM Irrigated area Rice 45 (1 ha) Crop area as percentage of the total area equipped for irrigation by month J F M A M J J A S O N D Rice-one Rice-two Maize Sweet potatoes Sugarcane Vegetables Bananas Citrus All irrigated crops Equipped for irrigation 3 Cropping intensity 171

16 Irrigation scheme ET = K c * ET o ET o : Reference crop evapotranspiration

17 Irrigation scheme Non-irrigated Irrigated

18 Irrigation scheme: Validation a) b) c) a) Mean annual simulated irrigation water requirements compared to irrigation water use in USA. b) Mean annual simulated and reported irrigation water requirements for countries in Asia. c) The lower values shown in b).

19 Irrigation water requirements 12 W 11 W 1 W 9 W 8 W 7 W 5 N a) 8 N 6 N 4 E 6 E 8 E 1 E 12 E 14 E a) 4 N 4 N 3 N 2 N 12 W 11 W 1 W 9 W 8 W 7 W 5 N b) 8 N 6 N 4 E 6 E 8 E 1 E 12 E 14 E b) 4 N 4 N 3 N 2 N a) b) 2 4 mm year a) Irrigation water requirements. b) Corresponding increases in latent heat fluxes Wm -2

20 Reservoir model 1 st priority: Irrigation water demand 2 nd priority: Flood control 3 rd priority: Hydropower production If no flood, no hydropower: Make streamflow as constant as possible River Non-irrigated part of grid cell Irrigated part of grid cell Reservoir Dam Water withdrawal point Water withdrawn from local river Water withdrawn from reservoir

21 Reservoir model 7q1 + irrigation water requirements: Naturalized inflow Simulated inflow Operational year Storage settings Q = ( + ) min Si 1 Qin Si 1 Send Qin Qmin E i day day= i day= i+ 1 day= i max, i res day

22 Reservoir model 1 st priority: Irrigation water demand 2 nd priority: Flood control 3 rd priority: Hydropower production If no flood, no hydropower: Make streamflow as constant as possible River Non-irrigated part of grid cell Irrigated part of grid cell Reservoir Dam Water withdrawal point Water withdrawn from local river Water withdrawn from reservoir Objective functions used to optimize Q: Irrigation: Flood protection: Hydropower: Water supply, navigation: 365 min min min min i= i= i= 1 Qr i ρηhg 365 Optimization scheme: SCEM-UA algorithm of Vrugt et al. (Water Resources Research, 23) 1 ( Qr i Q mean ) i= 1 ( Qd Qr ), Qd > Qr i i 2 ( Qr i Q flood ), Qr > Q flood

23 Reservoir model: Evaluation m 3 /s Columbia, The Dalles J F M A M J J A S O N D Model evaluation: 1) Columbia, 2) Colorado, and 3) Missouri River basins m 3 /s Naturalized streamflow Simulated, no irrigation, no reservoirs Observed streamflow Simulated, irrigation and reservoirs m 3 /s 42 Colorado, Glen Canyon J F M A M J J A S O N D Missouri, Hermann J F M A M J J A S O N D Percent irrigated > <.1 Dam

24 Irrigation water use: Validation Simulated (km 3 year -1 ) a) India b) c) 3 4 California Iran 2 3 Florida Pakistan 2 Thailand 2 1 China 1 Former USSR Indonesia 1 Texas Nebraska Reported (km 3 year -1 ) Reported (km 3 year -1 ) Reported (km 3 year -1 ) Mean annual simulated and reported irrigation water use (o) and simulated irrigation water requirements (+) in the conterminous USA. Groundwater withdrawals Diversions

25 Results: Irrigation water 12 W 11 W 1 W 9 W 8 W 7 W 5 N a) 4 N 4 N 2 N 3 N 4 E 6 E 8 E 1 E 12 E a) a) Irrigation water requirements b) Irrigation water uses c) Irrigation water deficits 12 W 11 W 1 W 9 W 8 W 7 W 5 N b) 4 N 4 N 2 N 3 N 12 W 11 W 1 W 9 W 8 W 7 W 5 N c) 4 N 4 E 6 E 8 E 1 E 12 E b) 4 E 6 E 8 E 1 E 12 E c) Irrigation water requirements NLDAS: 18 mm year -1 Asia: 16 mm year -1 Irrigation water uses NLDAS: 1 mm year-1 Asia: 1 mm year-1 4 N 3 N 2 N 2 4 mm year -1 Global terrestrial - precipitation: 8 mm year -1 - evapotr.: 4 mm year -1 Haddeland, I., T. Skaugen, and D.P. Lettenmaier, 26, Continental-scale water resources modeling, Nordic Hydrological Conference

26 Results: Streamflow 5 N 4 N 3 N 12 W 11 W 1 W 9 W W 7 W Percent irrigated areas > <.1 Dam Basin boundary m 3 /s 1) Columbia J M M J S N 5) Ohio m 3 /s 2) Colorado J M M J S N 6) Yenisei m 3 /s 3) Missouri J M M J S N 7) Lena m 3 /s 4) Arkansas J M M J S N 8) Brahmaputra N 6 N 4 N 2 N 4 E 6 E 8 E 1 E 12 E 14 E Columbia 2 Colorado 3 Missouri 4 Arkansas 5 Ohio 6 Yenisei 7 Lena 8 Brahmaputra 9 Mekong 1 Xi 11 Chang Jiang 12 Huang He m 3 /s m 3 /s J M M J S N 9) Mekong J M M J S N m 3 /s m 3 /s J M M J S N 1) Xi J M M J S N m 3 /s m 3 /s J M M J S N 11) Chang Jiang J M M J S N m 3 /s m 3 /s J M M J S N 12) Huang He J M M J S N Simulated, no reservoirs, no irrigation Simulated, reservoirs and irrigation Observed streamflow

27 HuangHe Results: Irrigation water use Irrigation water use (km3/year) Columbia Colorado Arkansas Missouri Ohio Yenisei Lena Ganges-B. Mekong Xi Changjiang

28 Results: Flow duration curves Fract. of max flow Fract. of max flow Fract Fract. 1 Columbia Yenisei Percent of time exceed. Colorado Missouri Ohio Ganges-Brah Percent of time exceed. Changjiang Percent of time exceed. 1) Simulated, no irrigation, no reservoirs 2) Simulated, irrigation and reservoirs 3) 2) divided by 1) Huang He Percent of time exceed.

29 Results: Streamflow 12 W 11 W 1 W 9 W 8 W 7 W Percent irrigated areas 5 N > N N.1-1 <.1 Dam 3 E 6 E 9 E 12 E 15 E 6 N 3 N km 3 month -1 fraction a) b) c) East Pacific West Atlantic Arctic J M M J S N J M M J S N J M M J S N 1) No reservoirs, no irrigation 3) Reservoirs and irrigation assuming 2) Reservoirs and irrigation water is freely available d) 96 6 e) Indian West Pacific J M M J S N J M M J S N 4) Reservoirs, no irrigation Effects on freshwater fluxes reaching the oceans. a) and b) represent rivers draining the NLDAS region to the Pacific and Atlantic Oceans, respectively. c) represents rivers draining northwards to the Arctic Ocean in the Asian region, while d) and e) represent river draining Asia to the Indian and Pacific Oceans, respectively. The lower panels show the results of simulations 2 through 4 divided by simulation 1.

30 Results: Continental streamflow NLDAS Asia km 3 month km 3 month Fraction 1..8 J F M A M J J A S O N D Fraction 1..8 J F M A M J J A S O N D 1) Simulated, no irrigation, no reservoirs 2) Simulated, irrigation and reservoirs 3) 2) divided by 1)

31 The Colorado River basin Percent irrigated > <.1 Dam a) Irrigation water requirements b) Evapotranspiration increase c) Changes in latent heat fluxes d) Changes in sensible heat fluxes e) Changes in surface temperatures 1 2 mm 5 1 Percent 1 2 Wm Wm o C Naturalized: Q: 42.3 mm year -1 ET: 335 mm year -1 Irrigation included: Q: 26.5 mm year -1 ET: 35 mm year -1

32 RCM-VIC Kelvin Kelvin No irrigation: Max air temp Irrigated: Max air temp 27 Irr-Noirr: Max air temp -2 Kelvin 33 Kelvin 2 Effects of irrigation on air and surface temperatures No irrigation: Min air temp Irrigated: Min air temp Kelvin 33 Irr-Noirr: Min air temp Kelvin 2 Colorado River basin Mean results, July 23 No irrigation: Max surface temp Irrigated: Max surface temp 27 Kelvin Irr-Noirr: Max surface temp -2 Kelvin No irrigation: Min surface temp Irrigated: Min surface temp 27 Irr-Noirr: Min surface temp -2

33 Conclusions The model does a reasonable job of reproducing the effects of management on selected large rivers. Reservoirs and crop irrigation water use has the potential of altering the natural hydrologic water balance of river basins. Simulated maximum monthly increases in streamflow, as a result of river regulations, are less than 3 percent, and are for Arctic rivers where winter flows are quite low. The largest monthly decrease in streamflow is about 3 percent, and is a result of flood control management and irrigation in the Western USA. Averaged over the NLDAS region and Asia, simulated consumptive irrigation water uses are 4.2 and 2.8 percent of simulated naturalized runoff, respectively. Given freely accessible irrigation water, the corresponding numbers are 7.6 and 4.4 percent. Averaged over larger regions, the changes in heat fluxes and surface temperature are small, but locally the changes can be significant.

34 References Haddeland, I., D.P. Lettenmaier, and T. Skaugen, 26, Effects of irrigation on the water and energy balances of the Colorado and Mekong River basins, Journal of Hydrology (in press) Haddeland, I., T. Skaugen, and D.P. Lettenmaier, 26, Anthropogenic impacts on continental surface water fluxes, Geophysical Research Letters (in press)