Historical Trend Analysis of A Terai Himalayan District Of Nepal : A Case Study

Abstract

This study work focused on key climatic variable rainfall together with temperature of the study area Morang District located in Eastern Development Region, Nepal. As rainfall is the ultimate natural source for the recharge of surface and groundwater resources, it became necessary to analyze the trend of rainfall. Rainfall and temperature data of 30 years (1982 to 2011) on daily basis was processed to find out the monthly, seasonal and annual rainfall and temperature variability by using nonparametric tests. The Mann-Kendall Test for monotonic analysis of trend together with non-parametric Sen‟s Slope Estimator was used to estimate the magnitude of trend. The trend of 30 years rainfall data has been drawn on monthly, seasonal and annual basis. The statistical analysis of whole reference time series data represents positive trend on annual basis. In summer, spring, pre-monsoon, monsoon, rabi and kharif seasons the rainfall trends are positive while in winter, autumn and post-monsoon seasons the precipitation trends are decreasing. Individually seven months (January, April, May, June, July, August and November) indicated rising trend while remaining five months (February, March, September, October and December) showed falling trend. Similarly, the trends of 30 years maximum and minimum temperature data have also been investigated on monthly, seasonal and annual basis. The trends showed that both maximum and minimum temperatures are rising irrespective of temporal scales. In case of maximum temperature, the month of January and cold winter season showed falling trend otherwise all other months and seasons showed rising trend while the minimum temperature trend analysis showed rising trend in all months and seasons.