Spatiotemporal Patterns of Hydrometeorological Extremes over 1986–2015 in Nepal

Abstract

To better understand the hydrometeorological mean conditions and changes in Nepal, this study analyzes annual and monthly changes of mean and extreme precipitation indices for 34 stations (1986–2015) and streamflow indices for 19 stations (different available periods ranging from 1962 to 2014). The annual and monthly precipitation–streamflow relations in the major basins of Nepal are also analyzed. Nepal has heterogeneous precipitation spatial patterns in its mean and changes. The spatial pattern of extreme precipitation shows that the dry regions are prone to dry extremes and wet regions are prone to wet extremes during the past three decades. However, the annual precipitation trend is decreasing in general and the monsoon-dominated regions, namely, southern, eastern, and central Nepal, are becoming drier with less intensive precipitation while the western region is getting wetter. The trend of annual precipitation on average is decreasing attherateof4.2mmyr-1. The risk of drought is increasing in Nepal as 100% of stations show a positive trend of consecutive dry days (CDD) and the all-Nepal trend is 0.8 days yr-1, which can put stress on the agriculture and health sector. The highest increase in CDD is at Ilam in the eastern hills with 2.9 days yr-1. The Southeast Asian monsoon index shows a statistically significant 1-month-lagged influence on country-wise precipitation in Nepal. The effect of decreasing precipitation is seen in the streamflow trend as the majority of stations show decreasing runoff in June and July, as opposed to an increase in the winter months. CDD and maximum 1-day (Rx1day) and 5-day (Rx5day) precipitation significantly decrease with elevation.