Unformatted text preview:

To Study the Various Factors Affecting the Summer Monsoon Rainfall in Nepal IntroductionSpatial Extreme Variability Categorizing Responsible Factors Monsoon Variability(IOD) (Prof. Yamagata, Dr. Saji)Modeling Output: (IOD) Atmospheric Brown Clouds (ABC) Aerosol over Nepal ( Source: Ramana et.al.2004) Differential Heating Over Different Region (ABC)(Source: Lau et.al. 2006) ImpactContd.. The red shade - increased sinking motions, and the blue shade - increased rising motions (ABC)(Ramanathan et.al.2005) Recent Modeling Output (ABC) ..Contd..For 70 years (1930-2000), Annual Mean surface warming trend: TRUTHENSO How important is ENSO to ISMR ? Rainfall Distribution in Nepal: Eastern >3000mm/Yr Western < 1000 mm/Yr Ichiyanagi (2007)CASE STUDY: Marshyangdi Subcatchment,Central Nepal…Case Study..Total Deficit Years: 13 Deficit (>13%): Year ’91,’92,’05,’06 agree with NOAA El Nino indices Total Excess Years: 20 Excess (>AnalysisISMR Lacks any long term trend (Kothyari and Singh,1996), ..Analysis..Shortcomings:Conclusion:To Study the Various Factors Affecting the Summer Monsoon Rainfall in NepalNaresh NeupaneThe University of Texas at AustinJackson School of GeosciencesDepartment of Atmospheric SciencesNov 18, 2008Introduction• >65% farming• Flood: 1993 (540mm in 24 hrs)• Lives: 1336• Family: 85,451(MOPE,2004)Spatial Extreme Variability• Flood event: 1994• Victims: 37 out of 75 districts• Droughts: 35 out of 75 districts(MOPE, 2004)Categorizing Responsible Factors • Indian Ocean Dipole(IOD)• Atmospheric Brown Cloud (ABC)• ENSO (El Nino/ La Nina)Monsoon Variability(IOD) (Prof. Yamagata, Dr. Saji)Modeling Output:(IOD)• IOD coincides with ENSO for 1992 and 1997• IOD does not coincide with ENSO esp. in the year 1961,1967 and 1994• Correlation between IOD and ENSO = 0.35 (Sajiet.al.1999)Atmospheric Brown Clouds (ABC)• Solar Dimming• Nuclei coagulate more cloud drops• Reduce solar radiation reaching the surface• Positive feedbackAerosol over Nepal ( Source: Ramana et.al.2004)Differential Heating Over Different Region (ABC)(Source: Lau et.al. 2006)Impact• Weakens Hadley Cell• Lesser rainfall over northern Africa (Ramanathan et.al. 2005)• Long term drought over northern China• Excessive rainfall over the southern China and India (Menon et.al.2002)Contd.. The red shade ‐ increased sinking motions, and the blue shade ‐ increased rising motions (ABC)(Ramanathan et.al.2005)Recent Modeling Output (ABC)• Observed rate of dimming for the period(1930‐2000) was ‐ 0.42 Wm‐2• Simulated rate of dimming was found to be ‐0.37 Wm‐2 (Ramanathan et.al. 2005)...Contd..• Simulated (blue) and observed (green) (Source: Ramanathan et.al.2005)• About 70% reduction in Incoming solar radiation has been balanced by the reduction in evaporationFor 70 years (1930‐2000), Annual Mean surface warming trend:• GHGs‐1998 is 0.8oK• GHG‐SO4‐1998 is 0.76oK• ABC‐1998 is 0.45oK• The Observed Trend i.e., 0.44 oKTRUTHABC has strong cooling effect !ENSOISMR• El Nino ‐ abnormal warming →Droughts(ENSO index < ‐1.0)• La Nina ‐ abnormal cooling → Floods (ENSO index >1.0)• The drought of 1992 in Nepal has been correlated with the ElNino of 1992‐1993 (Shrestha et.al.2000)How important is ENSO to ISMR ? • Ihara et.al 2007 discusses deficit in ISMR despite EL Nino event• Terray (1995) says, ENSO has no connection with ISMRRainfall Distribution in Nepal:Eastern >3000mm/YrWestern < 1000 mm/YrIchiyanagi (2007)CASE STUDY: MarshyangdiSubcatchment,Central Nepal…Case Study..Total Deficit Years: 13Deficit (>13%): Year ’91,’92,’05,’06 agree with NOAA El Nino indicesTotal Excess Years: 20Excess (>13%):Year ’84,’85,’89,’95,’96 agree with NOAA La Nina indicesAnalysis• IOD is independent of ENSO (Saji et.al. 1999)• Observed trend of rainfall variability matches to a good extent with the trend of ABC‐1998 than with the GHG+SO4( RamanathanEt.al.2005)• The simulation record shows that there is reduction of ‐5%(‐3%) between 1930 and 2000 (ABC‐1998) in the Indian rainfall amount. ISMR Lacks any long term trend (Kothyari and Singh,1996),0 50 100 150 200 250 300 350 400 450-80-60-40-2002040Time Period (1970-2006)Rainfall aomalies (mm)Rainfall Variation in Marshyangdi Catchment/Nepal..Analysis..• Monsoon Shifting towards the South !• Impact over Nepal ?• Overemphasizing GHG over ABC ?Shortcomings:• Lack of Ocean Data analysis by Ramanathan,2005• Impact of Increase of temperature over land upon the Ocean has not been considered• Overlooking the importance of number of weather stations and spatial variations• Barros et.al. 2000, in availability of radars or radiosonde networks in these regionsConclusion:• Recent simulation shows decrement of 3‐5% in ISMR and this fits better with ABC• ENSO agree with ISMR variability• Trend: short term 3 years and long term 13 years in Marshyangdi catchment• FUTURE: COMBINING IOD AND


View Full Document

UT GEO 387H - Lecture notes

Documents in this Course
Impacts

Impacts

2 pages

Load more
Download Lecture notes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lecture notes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lecture notes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?