The Impact of Irrigation on Land-Atmosphere Interactions and Indian Monsoon Precipitation

1. The Impact of Irrigation on Land-Atmosphere Interactions and Indian Monsoon Precipitation Ellen Douglas UMass Boston Adriana Beltrán-Przekurat CIRES UColorado Boulder Dev Niyogi Purdue University Roger Pielke, Sr. CIRES, UColorado Boulder Charles VörösmartyUNH

2. Magnitude of agricultural land use conversion • Humans have transformed one-third to one-half the earth’s land surface (Avissar et al., 2005). Cropland and pasture land ~40% of land surface (FAOSTAT) • Similar spatial scale as SST anomalies associated with ENSO (Pielke, 2005) Source: Marshall et al., 2004

3. Magnitude of agricultural land use conversion • Humans have transformed one-third to one-half the earth’s land surface (Avissar et al., 2005). Cropland and pasture land ~40% of land surface (FAOSTAT) • Similar spatial scale as SST anomalies associated with ENSO (Pielke, 2005) • Irrigated agriculture has expanded from 0.5 to 2.8 million km2 in 20th C (Postel 1993; FAOSTAT) Source: Marshall et al., 2004

4. Magnitude of agricultural land use conversion • Humans have transformed one-third to one-half the earth’s land surface (Avissar et al., 2005). Cropland and pasture land ~40% of land surface (FAOSTAT) • Similar spatial scale as SST anomalies associated with ENSO (Pielke, 2005) • Irrigated agriculture has expanded from 0.5 to 2.8 million km2 in 20th C (Postel 1993; FAOSTAT) • Irrigation water use comprises 70-80% of human water use globally. Source: Marshall et al., 2004

5. 5 to possibly 25% of global freshwater use exceeds long-term accessible supplies (low to medium certainty) • 15 - 35% of irrigation withdrawals exceed supply rates and are therefore unsustainable (low to medium certainty)  Recent analysis indicates 10-15% unsustainable globally.

6. - Increase in global vapor fluxes due to irrigated agriculture estimated to be ~2600 BCM/yr (Gordon et al., 2005). - Irrigation consumptive losses ~1200 BCM/yr (Vörösmarty et al, 2005) What are the impacts on regional weather and climate? How do these impacts affect human vulnerabilty? (Source: Gordon et al., 2005)

7. Difference in moisture patterns between natural vegetation and agricultural landscape (Pielke et al., 1997) • Increased moisture flux increases CAPE, which affects convection and precipitation patterns

8. GLC2000 (aggregated to 5-min resolution) • In India, 1 billion people live on 2.3% of global land mass.

9. GLC2000 (aggregated to 5-min resolution) • In India, 1 billion people live on 2.3% of global land mass. • Food production and livelihoods are highly dependent on occurrence and timing of summer monsoon rains.

10. GLC2000 (aggregated to 5-min resolution) • In India, 1 billion people live on 2.3% of global land mass. • Food production and livelihoods are highly dependent on occurrence and timing of summer monsoon rains. • > 90% of water use goes to irrigation, a great deal is due to groundwater mining

11. Indian Monsoon and society • South Asian human development has responded to millenial scale variability of Indian Monsoon • Wet phase ~10,000 to 7000 yr BP coincides with first human settlements in Pakistan Source: Gupta et al., 2006

12. Indian Monsoon and society • South Asian human development has responded to millenial scale variability of Indian Monsoon • Wet phase ~10,000 to 7000 yr BP coincides with first human settlements in Pakistan • Dry phase since ~4000 yr BP  eastward migration and irrigation development possibly as mitigation strategy. Source: Gupta et al., 2006

13. Vulnerability of the Indian Monsoon • Moisture-advection feedback • Pressure gradient between land and ocean (driver) reinforced by moisture carried by Monsoon • Two possible stable states (Zickfield et al., 2005) • Wet state: > 4mm/day (current state) • Dry state: < 1mm/day

14. The Impacts of Water Resource Vulnerability in India (Douglas et al., 2006).

15. Possible tipping point mechanisms for the Indian Monsoon • Planetary albedo • Vegetation + clouds • CO2 concentration • Aerosols • Any perturbation in the radiative budget over the sub-continent Source: Zickfeld et al., 2005

16. POT CRP WWF Ecoregions (Olson et al, 2001) IRR

17. Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indian Monsoon Belt (Douglas et al., 2006) • Estimated seasonal (Kharif and Rabi) cropland and irrigated land areas by Indian state • Computed differences in 1-D, uncoupled latent heat (LH) fluxes between POT and IRR scenarios using terrestrial water balance model • Proportioned changes in LH flux between surface water and groundwater irrigation.

18. Area-averaged mean annual vapor (LH) flux increased by 17% (9 Wm-2) 7% in wet season 55% in dry season Two-thirds (6 Wm-2) of this increase was due to irrigation. About twice that reported by deRosnay et al. (2003).

19. Changes in latent heat flux (W m-2) Kharif (wet) Rabi (dry)

20. The Impact of Agricultural Intensification and Irrigation on Land-Atmosphere Interactions and Indian Monsoon Precipitation – A Mesoscale Modeling Perspective (Douglas et al, GPC special issue) • Performed preliminary 3-D analysis of three land cover/ land use scenarios: POT, CRP, IRR • Computed differences in LH, SH, VP, Prec, Temp, PBL between each scenario • Analysis over smaller domain (to avoid influences of terrain) • Analysis over larger domain (to compare with Douglas et al, 2006)

21. LATENT HEAT SENSIBLE HEAT BOWEN RATIO (SH/LH) a) b) c)

22. Temp Vapor Similar to deRosnay et al (2003) Findings of 3.2 Wm-2 PBL

23. RAMS Similarities and difference between WBM and RAMS results WBM (kharif)

24. Effect of land cover conversion on albedo CRP to IRR POT to IRR

25. Summary and conclusions • Surface energy and moisture fluxes are sensitive to the irrigation intensity. • Change from potential vegetation to irrigated agriculture resulted in a statistically significant reduction in SH = 11.7 Wm-2 over all of India • Increased regional moisture flux (1 g/kg) caused reduction in the surface temperature (1-3 C) and changes in mesoscale precipitation. • Albedo (prescribed parameter) slightly reduced, but further analysis needed. • Affect on PBL may affect pressure gradient that drives the Monsoon circulation.