Climate change is primarily resulted from human-made activities resulting greenhouse gases emissions and appearing as an increase in temperature and variability in precipitation. According to NASA (2009), in total, average global temperatures have increased by about 0.8°C (1.4°F) since 1880 (the year that modern scientific instrumentation became available to monitor temperatures precisely). World Meteorological Organization (2011) reported over the ten years from 2001 to 2010, global average temperature is 0.46°C (0.83°F) above the 1961-1990 average. This is the highest ever recorded for a 10-year period since the beginning of instrumental climate records.
The general trend in the Nepal record is quite similar to what has been found in the global records although the magnitude of trends are different, suggesting that the climate variations and changes in Nepal are impacted by global climate change. Department of Hydrology and Meteorology (DHM) estimated from 1977 and 1994, the mean annual temperature to have increased by 0.06°C, and is projected to increase by another 1.2°C by 2030, 1.7°C by 2050, and 3.0°C by 2100. Analysis on rainfall data from station records all over Nepal show distinct cyclic characteristics but does not reveal any significant trends, as observed in temperature records.
Nepal Engineering College under the research grant of International Development Research Center, Canada, analyzed various attributes of rainfall and temperature for seven stations of Kathmandu (Khumaltar, TIA, Godawari, Changu Narayan, Naikap, Panipokhari and Sankhu) selected considering their proximity to the peri-urban research sites of the ongoing project.
The analysis of temperature record showed a clear decrease in number of days below 0°C and increase in number of hot days (> 30°C). The highest and the lowest temperature of both daily Tmin (Minimum Temperature) and daily Tmax (Maximum Temperature) showed an increase. This increase in temperature was the lowest for the summer season and the strongest for fall and winter season. Tmin showed an average increase of 0.04°C per year and Tmax showed on average an increase of 0.05°C per year. More clearly, days and nights are both becoming warmer and cool days and cool nights are becoming less frequent. Similarly summer days with maximum temperatures above > 30°C are also increasing.
While the changing trend of temperature can be expressed in terms of the mean over time and the amount of variance about the mean, other meteorological variables require more complicated statistical calculations. For instance, rainfall is episodic. Considering WMO statement, in certain parts of the world especially in the arid regions of the world precipitation are likely to decrease whereas in the northern hemisphere the likelihood is that the precipitation would increase. In Nepal, much of the annual rainfall falls in a short rainy season. Analysis on rainfall data from station records all over Nepal does not reveal any significant trends.
The analysis of rainfall data from the above mentioned seven stations for understanding the long term rainfall trend in Kathmandu showed no clear increasing or decreasing trend in the number of days with rainfall. Similarly, the trend for the total annual rainfall is not clearly defined. Upon concentrating the analysis for monsoon period (June to September), no defined trend could be drawn. An increase in the number of extreme rainfall events (daily rainfall > 50mm) was found but concerning the intensity of rainfall conducted for monsoon period in the study no recognizable pattern could be concluded.
Uncontrolled urbanization and spreading infrastructure in Kathmandu has contributed to reduced agriculture land, increasing congestion, and environmental degradation associated with the poorly managed disposal of solid and industrial wastes and other forms of pollution. An increased frequency of extreme weather events attributed to anthropogenic climate change can make the prospects for environmental sustainability and human security disconcerting for example in unplanned land p. Increases in seasonal temperatures are likely to affect agricultural production and yield. Higher temperatures have also been associated with an increase in diarrhea, mild winters tend to increase rodent-borne diseases, and can also increase dengue-fever transmitted by mosquitoes. Though the amount of rainfall has not undergone decline, the water availability has been declining. This decline is commonly perceived to be ensued from declining rainfall. Therefore, strengthening the adoptive strategies in Kathmandu need activities investigating knowledge, expertise and resources to raise awareness against the challenges of pressure on resources and environment associated with urbanization, changing climate and the compounded effects.