Altitudinal variability of monsoon precipitation over Mountainous Region
Prasamsa Singh (1), Shiva Bhakta Prajapati (2)(1: Department of Biological Sciences and Environmental Science, Kathmandu University,
Dhulikhel, Nepal, email: singh@ku.edu.np
2: Department ofshiva@dhm.com.np )Hydrology

andMeteorology,

Kathmandu,Nepal

email:

Abstract
The study conducted some investigations to know the relationship between topographic effects on rainfall distribution withregards to the topographic elevation over Mountainous region. Comparison of relationship between topographic effects onrainfall distribution with relation to the topographic elevation using ground based data of one hundred and ninety one rain
gauge stations within domain of latitude 27.30' to 29.40' and longitude 80.00' to 84.00' of period June - August (1998- 2000)
and Tropical Rainfall Measuring Mission/ Precipitation Radar (TRMM/ PR) within domain latitude 26.00' to 32.00' andlongitude 75.00' to 80. 00' of the same duration are characterized relatively well. Digital elevation map (DEM) with spatial
resolution 30 sec (Gtopo30) is used for spatial topographic study. Much attention was focused on "effective height for
precipitation" i.e. topographic height where amount of rainfall is high. It was found through investigation that the rainfall
decreases beyond 1800m using ground based data and rainfall decreases beyond 2100m using TRMM data.
Keyword: precipitation, elevation, monsoon,

1. Introduction
Spatial and temporal variation of precipitation
distribution is important to know to study the detailclimatic study. It's very important to know the variationof precipitation with relation to elevation in themountainous country like Nepal to know the potential ofwater resources and rational utilization of waterresources.
The fluctuation of rainfall distribution depends on
various factors concerning atmospheric condition or
topographic features, i. e. moisture source, wind speed,
wind direction, topographic elevation, slope orientation,
barrier characteristics, scale of mountains and otherfactors. Investigations have been conducted on therelation between such factors and precipitation
distribution (e. g. Suzuki, 2004; Kuraji, 2001)
The study focused on the relation between topographic
height and rainfall amount over Himalayan region.

2. Data Description
The research is conducted using ground-based dataobserved by rain gauge and using satellite data observedby Tropical Rainfall Measuring Mission (TRMM). Theused ground based data is within domain of latitude
27.30' to 29.40' and longitude 80.00' to 84.00' of period
June - August (1998- 2000) and satellite data is withindomain latitude 26.00' to 32.00' and longitude 75.00' to80. 00' of the same period. Both ground based data andTRMM data is averaged for one-degree X one-degree

grid. The study is done for 500m to 3000m elevation
height with averaging precipitation for each 100 m.
3. Results, Discussion and Conclusions
The figure 1 shows the relation between topographic heightand precipitation distribution using ground-based data. The
figure declears that precipitation increases gradually withincrease of elevation height up to 1800m then gradually
decreases with increases of elevation height.
The figure 2 shows the relation between topographic heightand precipitation distribution using TRMM data. The figure
declares that precipitation decreases with increase of elevation
height beyond 2100m but increase of precipitation withincrease of elevation height isn't clear

Though TRMM PR has sampling error due to swath width of
216m and data period is only for 3 years it shows almost same
pattern in relation with topographic elevation.

A convective phenomena generated by topography appear inwindward side. So further study will be done for altitudinalvariation of precipitation in windward and leeward sides ofmountain separately.

Topographical Elevation (m)

4000
3000
2000
1000
00500

1000

1500

2000

2500

Monsoon Precipitation (mm)Fig. 1: altitudinal variation of precipitation usingground based data using rain gauges over latitude
27.30' to 29.40' and longitude 80.00' to 84.00' of period
June - August (1998- 2000)

Topographical Elevation (m)

4500
4000
3500
3000
2500
2000
1500
1000
50000500

1000

1500

2000

2500

3000

Monsoon Precipitation (JJA, mm)

Fig. 2: altitudinal variation of precipitation using
space data using TRMM data over latitude 26.00' to32.00' and longitude 75.00' to 80. 00' of period June August (1998- 2000)

Reference:
Kuraji, K., Punyatrong, K. and Suzuki, M. (2001): Altitudinalincrease in rainfall in the Mae Chaem watershed, Thailand. J.
Meteor. Soc. Japan, 79(1B), 353-363
Suzuki, Y., Nakakita, E., Hasebe, M. and Ikebuchi, S. (2004):
Study on rainfall- Topography relationships in Japan withregard to the spatial scale of mountain slopes, Sixth
International Symposium on Hydrology Application ofWeather Radar.