Factors affecting monsoon precipitation in Nepal

Factors affecting Monsoon Precipitation in Nepal

- Sagar P. Parajuli

05/01/2013

Motivation• Agriculture is the backbone of economy in

the Indian subcontinent including Nepal, India, Bangladesh

• Agriculture of this region mainly depends on monsoon precipitation

• Natural disasters such as flooding, landslides and lightening are frequent

• Drought affect local water resources and worsen water shortage

Fig. 1. ISM, Indian Summer Monsoon; EASM, East Asian Summer Monsoon. Arrows show 60-year mean summer (June, July, August) wind fields based on NCEP/NCAR reanalysis. Adapted from (Wang et al. 2010)

Indian Summer Monsoon

Figure 2. 13 years average JA precipitation: TRMM composite climatology(0.5 *0.5 degree)

http://gcmd.gsfc.nasa.gov/KeywordSearch/Metadata.do?Portal=GCMD&KeywordPath=[Project%3A+Short_Name%3D%27TRMM%27]&EntryId=GES_DISC_TRMM_TCC_V6&MetadataView=Full&MetadataType=0&lbnode=mdlb5

Factors considered

• ENSO/Pacific QDO

• Topography

• Tibetan plateau heating

• Aerosols

ENSO Topography Tibetan Plateau Aerosols

Precipitation trend in Nepal• Decadal oscillation (11 years cycle) seen in Nepal

precipitation trend (Shrestha et al. 2007)

• Pacific QDO’s relation with Nepal precipitation is not instantaneous but the maximum (minimum) precipitation anomalies occur 1–2 years prior to the cold (warm) extremes of the Pacific QDO (Wang et al. 2013)

ENSO/QDO Topography Tibetan Plateau Aerosols

Station-based mean annual precipitation in Nepal (Baidya S. 2007)

TRMM Mean monthly precipitation (0.25*0.25 degree) inNepal

ENSO/QDO Topography Tibetan Plateau Aerosols

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter10/elnino.html

Relation between ENSO and Indian Monsoon

ENSO/QDO Topography Tibetan Plateau Aerosols

(Kumar, K. et al. 2007)

Figure 2. Composite SST anomaly for drought (shaded) and drought-free (contours) El-Nino years

ENSO/QDO Topography Tibetan Plateau Aerosols

(Kumar, K. et al. 2007)

Fig 3. Model simulation results (CAM 3.5.18, 1992-1997) of average JJA Surface wind (arrows) and precipitation (shaded) for (a) Standard topography, (b) All topography removed

(a) (b)

ENSO/QDO Topography Tibetan Plateau Aerosols

(Boos et al. 2010)

Figure 4. (c) Model simulation results of average JJA surface wind (arrows) and precipitation (shaded) with Tibetan topography removed (d) Precipitation and 850 hpa wind anomaly for JJA relative with Tibetan plateau albedo = 1.

(c) (d)

ENSO/QDO Topography Tibetan Plateau Aerosol

(Boos et al. 2010)

ENSO Topography Tibetan Plateau Aerosols

Figure 5. (a) Time-latitude cross section of TOMS AI anomalies during high aerosol loading years over Himalayan region (b) same as (a) but for precipitation (mm/day)(c) Area mean daily aerosol index over Himalayan region

(Lau et al. 2006)

ENSO Topography Tibetan Plateau Aerosols

Figure 6. 200 hpa (left) and 925 hpa (right) geopotential height (contours) and wind (arrows) for July/August 2012 from ERA-Interim reanalysis. Closer phi contours means colder and wider means warmer region.

ENSO Topography Tibetan Plateau Aerosols

Conclusions• Himalayan topography, moisture flux from bay of

Bengal, tropospheric absorbing aerosols, strong summer heating over the Tibetan plateau and Pacific QDO all affect precipitation in Nepal in varying degrees

• The concentrated and highly convective monsoon precipitation along the Nepal Himalayas is difficult to simulate with climate models (Shrestha et al. 2006)

• Precipitation trend in Nepal is unique and uncorrelated with that of India (Wang et al. 2010)

• Accurate forecasting of monsoon precipitation requires consideration of all of the above-mentioned factors

Thank you!

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