No abstract

This study identified summer and annual drought events using the Standard Precipitation Index (SPI) for 107 stations across Nepal from 1977 to 2018. For this, frequency, duration, and severity of drought events were investigated. The SPI4 and SPI12 time scales were interpolated to illustrate the spatial patterns of major drought episodes and their severity. A total of 13 and 24 percent of stations over the country showed a significant decreasing trend for SPI4 and SPI12. Droughts were recorded during El Niño and non-El Niño years in Nepal. Among them, 1992 was the worst drought year, followed by the drought year, 2015. More than 44 percent of the locations in the country were occupied under drought conditions during these extreme drought events. Droughts have been recorded more frequently in Nepal since 2005. The areas of Nepal affected by extreme, severe, and moderate drought in summer were 8, 9, and 18 percent, while during annual events they were 7, 11, and 17 percent, respectively. Generally, during the drought years, the SPI and Southern Oscillation Index (SOI) have a strong phase relation compared to the average years.

<p>The great Himalayas, the world’s highest mountain system, is home to millions of people and hundreds of unique species. It has one of the world's largest concentrations of cryospheric components (glaciers, snow, and permafrost). The Himalayas supply continued meltwater to some of Asia’s greatest river systems and play a vital role in the South Asian monsoon environment by guarding theIndian subcontinent from the dry, cold air masses of central Asia and blocking the warm, moist airflow from the Indian Ocean. Unfortunately, this water tower has been experiencing rapid changes driven by climate change in recent decades. Changes in this region have had and will continue to have major negative consequences for people living in the area and globally. However, changes in the climate extremes and their consequences have not been understood well yet because of the extreme topography that hinders the establishment and maintenance of monitoring networks. We will introduce some outstanding ongoing research activities in understanding key processes and changes in high-mountain meteorology, climate extremes, and glacier evolution over the southern slopes of the Himalayas. Results suggest that elevation-dependent warming accompanied by rapid glacier retreat is accelerating in the region. In addition, climate extremes are likely to increase with intensifying drought and floods. </p> <p> </p> <p> </p>

The frequency of winter drought episodes marked frequently in the recent decade. This study examined the time series indices of drought variability over Nepal using historical data of 42-years (1977–2018) for 107 stations using Standardized Precipitation Index (SPI). Monthly rainfall was used as input variable to generate the output for SPI time scales of each station. SPI threshold was used to identify severity, frequency, duration, and spatial extent of the drought episodes. The SPI3 output showed occurrence of major eight drought episodes. Among these years, dryness signals identified the worst drought episode in the year 2006. However, in regional prospective the western region observed extreme drought episode in 2009. There was distinct drought dynamics in each major drought event over the western, central and eastern Nepal. Spatial variability for SPI3 time scale was interpolated to depict spatial patterns of major drought episodes with their severities. The areas of Nepal affected by extreme, severe and moderate drought in winter were 4, 21 and 37%.

The study was conducted using rainfall time-series data for 42 years from 1977 to 2018. We have identified seven large monsoon deficient years. Among these years, 1992, 2009, and 2015 consisted of El Niño episodes which quantify significant rainfall deficits 19.29, 13.6, and 17.59 % respectively from an average rainfall. With some exceptions, all El Niño years observed deficit rainfall. On El Niño years averaged deficit rainfall was approximately nine percent below than the average monsoon rainfall. The eastern region observed the large deficient monsoon years frequently than the central and western regions of Nepal. The central region recorded large spatial variability of average summer rainfall ranging from less than 200 mm/months in lesser Himalayans to more than 3,000 mm/months in mid-mountainous region. The western region had observed a large deficient summer monsoon anomaly 45 % in the year 1979. Similarly, the central region had 31 % deficient summer monsoon anomalies in 1992, and the eastern region observed 25 % deficient anomalies in 1982. There was a strong correlation between the Nepal Summer Monsoon Rainfall (NSMR) and Southern Oscillation Index (SOI). Generally, large negative/positive magnitude of SOI on the Indian and Pacific Ocean has link to weakening/strengthening NSMR.