Rainfall Pattern Over Kathmandu Valley During Summer Monsoon Season and its Long - Term Change
Date
2008
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Central Department of Hydrology and Meteorology
Abstract
In this study, the spatial variability of rainfall over Kathmandu valley is
investigated on the basis of observational record of rainfall from 15 stations of valley for
the period 1970-2005(With more than 10 years data in each station).The spatial distribution
of summer monsoon rainfall is similar to the annual distribution with the highest rainfall
pocket area in the Northwestern mountain in the periphery of Kakani with more than 2300
mm of mean monsoonal rainfall, while the lowest rainfall is found in southern side of
valley floor in the periphery of Khumaltar with average monsoonal rainfall less than 950
mm. Rainfall pockets over valley are also noted in the periphery of Mountain stations
Nagarkot, Godavari, Thankot, Sundarijal and Sankhu with mean monsoonal rainfall greater
than 1500 mm. Inter annual variability of monsoonal rainfall is found to be relatively lowin the central part of valley floor than that of the base and top of mountains.
Based on daily rainfall data of 6 stations of valley for the period of 1971-2005,
overall (Valley average) trend on various rainfall characteristics over Kathmandu valley
during monsoon season are found as:
1) Overall (Valley average) rising trend in total monsoon rainfall but it does not
have statistical significance. 2) Overall (Valley average) significant rising trend in
no. of rainy days (> 1 mm /day) in Kathmandu valley. (At 5% level) (3) Overall(Valley average) significant rising trend (at 1% level) in no. of days with
precipitation rate 0.1-10 mm /day but the rising trend on that threshold in valley
floor is not significant. 4) Though, there is overall (Valley average) falling trend in
rain of categories 60-90 mm /day in valley, it doest have statistical significance. (5Overall (Valley average) rising trend in accumulated rain with rain rate 40-60 mm
/day and > 90 mm /day with low statistical significance.
Study of diurnal variability of rainfall in the valley floor has also been carried out by using
hourly data of Kathmandu airport for the period 1992-2002 .The result shows the two
pronounced peak, one in midnight and another in evening.
Description
Keywords
rainfall, monsoonal rainfall