Variability of Extreme precipitation Events in the Core of the North American Monsoon
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Variability of Extreme precipitation Events in the Core of the North American Monsoon. Tereza Cavazos 1 Cuauhtémoc Turrent 1 Dennis P. Lettenmaier 2 1 CICESE , 2 University of Washington. Fourth Symposium on Southwest Hydrometeorology Tucson, AZ, 20-21 September 2007. 2007 .

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Variability of Extreme precipitation Events in the Core of the North American Monsoon

Tereza Cavazos1

Cuauhtémoc Turrent1

Dennis P. Lettenmaier2

1CICESE, 2University of Washington

Fourth Symposium on Southwest Hydrometeorology

Tucson, AZ, 20-21 September 2007

2007


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Introduction the North American Monsoon

  • Semiarid climate

  • Annual P < 700 mm y-1

  • Important producers of grains,

  • vegetables, grasses, and cattle

  • Maximum precip variability

  • (Gutzler 2004)

  • Persistent droughts and heavy

  • rains  impact in agriculture

  • and water availability

Core Monsoon


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Core Monsoon the North American Monsoon

  • Last two decades: strong floods

  •  Severe damage (Bitrán, 2001), but also

  • benefits recharge of major dams (CNA, 2004)

  • Annual increase in heavy rains (P95, P99)

  • (Groisman et al. 2005, Alexander et al. 2006)

  • Future projections:

    • Increase in aridity and much less water

    • availability (IPCC, 2007; Seager et al. 2007)

    • Changes of extremes will be more important

    • than changes in mean precipitation


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Objectives the North American Monsoon

  • To investigate trends in extreme

  • precipitation events (P95) in the

  • core monsoon

  •  Monsoon derived extremes (non TC)

  •  Tropical cyclone derived extremes (TC)

  • To examine the role of the

  • land-sea thermal contrast in the

  • initiation of extreme events


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Data the North American Monsoon(JJAS, 1950-2003)

  • Daily precipitation from 39 stations from SMN/IMTA (Eric III)

  • Daily gridded precipitation (1/8o resolution) from the UW

  • Eastern Pacific hurricane tracks – 550 Km from the monsoon (Unisys)

  • Daily composites of atmospheric variables from NCEP Reanalysis (NOAA/CDC composites web page)

  • Weekly SSTs from in situ and satellite data (OISSTV2, Reynolds et al. 2002)


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Methodology the North American Monsoon

  • Quality control of 39 station data from ERIC III

  • Daily and seasonal index of the core monsoon (CMI)

  • Daily precipitation extremes (top 95% of wet days) Thresholds of P95:

    • CMI: 14.5 mm d-1

    • Coastal stations (0 – 500 m ASL): 50 mm d-1

    • Mountain stations (>500 m ASL): 42 mm d-1

  • Extremes derived from TC rainfall and from monsoon rainfall (non TC)

  • Trends, statistical significant changes (p < 0.05): Mann-Kendall test (Frequency, intensity, and seasonal contribution of extreme events)


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    Results the North American Monsoon

    Seasonal rainfall Index (JJAS )

    There is not a long term significant linear trend

    JJAS P61-90 = 490 mm

    JJAS P77-03 = 481 mm


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    Change in the intensity of P95 the North American Monsoon

    Significant increase in the intensity of extreme events, but not in the frequency

    Based period: 1961-1990


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    P95 Seasonal Contribution (%) the North American Monsoon

    In 1980-2000 there were 16 TCs that affected the core monsoon and

    5 made landfall:

    Hurricane Paul in 1982

    and Hurricanes Lydia, Ismael, Fausto, and Isis in the 1990s


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    Mtn P95 Contribution (%) the North American Monsoon

    Mtn: > 500 m ASL

    The total seasonal % contribution of P95 in mountain sites shows a significant increase of 1.5% per decade

    Coastal stations did not show any significant changes


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    TC-derived extreme rainfall the North American Monsoon

    JJAS: 1981-2003

    UW gridded precipitation (mm d-1)

    Between 1980 and 2003, Sinaloa was the second most affected state, after Baja California, by TCs (CNA, 2004)


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    WHWP, SST > 28.5 the North American MonsoonoC

    (Wang et al. 2006)

    Forcings: surface Tan (oC)

    One week before onset of extreme events in the core monsoon

    (A) TC: surface Tan (oC) (B) non TC: surface Tan (oC)

    +

    -

    Thermal gradient (> 1oC)

    TC highest frequency: September non TC highest frequency: Jul-Aug


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    (C) TC: air Tan ( the North American MonsoonoC), t=-5d (D) TC: V850an (m s-1), t=1d

    Forcing mechanisms

    Large land-sea thermal gradient (> 1oC)


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    Onset the North American Monsoon

    (E) TC: OLRan (Watts m-2), t=1d (F) TC: air Tan (oC), t=1d


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    August 2007 the North American Monsoon


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    Hurricane Henriette (Cat 1) 5 Sep 2007 the North American Monsoon

    Hurricane Felix (Cat 5)

    (mm d-1)

    PRECIPITATION:

    12Z 05 Sep - 12Z 06 Sep 2007

    (CPC-NOAA)


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    Conclusions the North American Monsoon

    • Intensity and seasonal contribution of extreme events in the core monsoon have increased significantly

    • Especially TC-derived extremes and in mountain sites

    • Frequency of extremes and seasonal rainfall do not show a significant linear trends

    • Extreme events in coastal stations do not show significant changes

    • TC-derived extreme events are characterized by

      • La Niña-like conditions

      • Strong land-sea thermal contrast near the study area, and

      • Large Western Hemisphere warm pool


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    Ongoing Work the North American Monsoon

    • Numerical investigation of the land-sea thermal contrast (MM5)

      • Indices to characterize the intensity of monsoon onset (C. Turrent)

      • Seasonal predictability of the monsoon based on soil moisture (Zhu et al.)

      • Sensitivity analyses of different monsoon years (C. Turrent, Zhu et al.)

    • Climate projections of extremes for the 21st Century (S. Arriaga)