Analysis of Heat Wave over Nepal

Abstract

Climate change imposed negative impact on socio-economic sectors of the mountainous region like Nepal. The 21 st century has brought many records breaking warm year. Such warm periods brought many health-related problems, heat wave is one among them. Daily maximum temperature data of 46 stations of DHM is used to calculate the heat wave (HW)patterns over the country. To better understand the regional pattern of HW all the stations are further classified into 6 different regions: East Terai, Central Terai, Western Terai, Eastern Mountain, Central Mountain and Western Mountain based on the 3 large river basins (Koshi, Gandaki and Karnali). The percentile-based method is used for the calculation of the HW. The 90 th percentile values are used as the threshold and HW is declared after the daily maximum temperature on exceeding the threshold and the normal temperature of the station by 4° C for at least 3 consecutive days. Based on the criteria, HW’s different characteristics like the total number of events, total days of HW, longest event, average days in HW, Maximum deviation of temperature in HW, the onset date of HW and the withdrawal date of HW are calculated using MATLAB and MS-Excel. The western region records the highest frequency and total heat wave days. The central and western mountain region shows the highest maximum temperature deviation than the Terai regions. Although the HW events are more severe in the mountain region but terai region shows consistent severe HW in these regions. The average days of heat wave event throughout the country is 2.6 days. Also, the monsoon event controls the heat wave events. The ElNino phenomena shows no significant relation with the heat wave but the peak of the heat wave is found at ElNino+1 year. The criteria used in this study is very easy to calculate and can be used for the national decision-making process.