Climate Controls and Climate Classification

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Nepal's Climate Control Factors

Nepal's climate is controlled by a number of factors on meso, macro, and micro scales.


Macro scale factors:

• Nepal is a land-logged country.  Its capital, Kathmandu, is located at 27°42′N 85°20′E.  The country is subject to northern hemisphere seasonality.

Meso scale factors:

• Topography: Nepal is bordered on the north by a large mountain range.  The Himalayas protect the region from cold, southerly polar air. 

  

  The Kathmandu Valley, along with the rest of Nepal, is sheltered to the north by the Himalayas.  Kathmandu itself is surrounded by higher elevation terrain.  Its lower altitude allows for slightly higher temperatures in the city itself.   Image: University of Tokyo 2010



• Nepal is subject to the ITCZ as a major contributor to its weather patterns.



During the summer, the intertropical convergence zone drops equatorial moisture onto Nepal. This accounts for Nepal's summer rainy season. During the winter, the ITCZ is far off the Indian coast resulting in predominantly cooler, dry air over the region. Image: http://pages-142.unibe.ch/about/national/indonesia/itcz.html

 Micro-scale climate controls:

• Local topography: The Kathmandu valley, like all valleys, is subject to cold air accumulation.  During the day, the sun heats the valley floor.  The warm air begins to rise, creating wind, and the cold air ponds in the valley. During the summertime, this can lead to thunderstorms as warm, moist air rushes out of the valley into the higher topography.
• Urban heat island effect: in Kathmandu, a growing population in conjunction with a high rate of urban development contribute to higher city temperatures.  The images below show the factors that contribute to this heat island effect in Kathmandu including high population density and land use changes.




Kathmandu, the most densely populated region in Nepal, is subject to heat island effect as part of its micro-scale climate controls.
http://www.websters-online-dictionary.org/images/wiki/wikipedia/en/thumb/f/f5/Population_density_map_of_nepal.png/24.png

  



This map shows changes in land use in the Kathmandu valley sononymous with urban heat island effect.  Red areas indicate extreme urban development including higher incidences of paved roads and dense building structures.  Increased development has also lead to the loss of vegetation in the surrounding area, which further compounds heat island effect.  Kathmandu's population was 1,006,656 as of the 2011 Nepal Census.  Image: University of Tokyo 2010.

Climate trends:

• In conjunction with global trends, temperatures in Nepal are climing steadily. 

Ths graph reflects temperature data for Kathmandu in January and July over a span of 15 years.   This weather station's data only goes as far as back as 1997 and only provides maximum temperature data to the public.  However, when plotted on a graph, an overall positive trend is visible for both summer and winter, indicating that temperatures have been gradually increasing over this time span.  Source: weatheronline.co.uk 

Climate classification:

• The following image depicts Nepal's climate as defined by the Koppen-Geiger climate classification system.  Kathmandu is located in the humid subtropical region of Nepal.

The Koppen-Geiger climate classification system designates two climates in Nepal.  The southern-central portion of the country is classified as CWa (humid subtropical) while northeast and northwest Nepal are classified as CWb (highland subtropical).  Image: University of Melbourne

References:

http://www.wrh.noaa.gov/mso/educate/wind1.html

"National Population Census 2011". National Planning Commission Secretariat, Central Bureau of Statistics (CBS), Government of Nepal. September 2011. http://census.gov.np/