Rising Precipitation Extremes across Nepal

Ramchandra Karki,Jürgen Böhner,Shabeh Ul Hasson,Thomas Scholten,Udo Schickhoff

doi:10.3390/cli5010004

Ramchandra Karki, Jürgen Böhner + Show 3 more

Open Access

https://doi.org/10.3390/cli5010004

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Abstract

As a mountainous country, Nepal is most susceptible to precipitation extremes and related hazards, including severe floods, landslides and droughts that cause huge losses of life and property, impact the Himalayan environment, and hinder the socioeconomic development of the country. Given that the countrywide assessment of such extremes is still lacking, we present a comprehensive picture of prevailing precipitation extremes observed across Nepal. First, we present the spatial distribution of daily extreme precipitation indices as defined by the Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI) from 210 stations over the period of 1981–2010. Then, we analyze the temporal changes in the computed extremes from 76 stations, featuring long-term continuous records for the period of 1970–2012, by applying a non-parametric Mann−Kendall test to identify the existence of a trend and Sen’s slope method to calculate the true magnitude of this trend. Further, the local trends in precipitation extremes have been tested for their field significance over the distinct physio-geographical regions of Nepal, such as the lowlands, middle mountains and hills and high mountains in the west (WL, WM and WH, respectively), and likewise, in central (CL, CM and CH) and eastern (EL, EM and EH) Nepal. Our results suggest that the spatial patterns of high-intensity precipitation extremes are quite different to that of annual or monsoonal precipitation. Lowlands (Terai and Siwaliks) that feature relatively low precipitation and less wet days (rainy days) are exposed to high-intensity precipitation extremes. Our trend analysis suggests that the pre-monsoonal precipitation is significantly increasing over the lowlands and CH, while monsoonal precipitation is increasing in WM and CH and decreasing in CM, CL and EL. On the other hand, post-monsoonal precipitation is significantly decreasing across all of Nepal while winter precipitation is decreasing only over the WM region. Both high-intensity precipitation extremes and annual precipitation trends feature east−west contrast, suggesting significant increase over the WM and CH region but decrease over the EM and CM regions. Further, a significant positive trend in the number of consecutive dry days but significant negative trend in the number of wet (rainy) days are observed over the whole of Nepal, implying the prolongation of the dry spell across the country. Overall, the intensification of different precipitation indices over distinct parts of the country indicates region-specific risks of floods, landslides and droughts. The presented findings, in combination with population and environmental pressures, can support in devising the adequate region-specific adaptation strategies for different sectors and in improving the livelihood of the rural communities in Nepal.

Highlights

Precipitation extremes are one of the major factors that trigger natural disasters, such as droughts, floods and landslides, which subsequently cause the loss of property and life, and deteriorate socioeconomic development
The spatio-temporal variation of the computed daily precipitation extremes has been analyzed from long-term continuous records available from 76 stations over the period of 1970–2012 using a robust non-parametric Mann−Kendall [33,34] trend test and the trend-free pre-whitening (TFPW) procedure
Trends at local stations are further assessed for their field significance over the seven distinct physio-geographic regions of Nepal, in order to identify the most dominant patterns of changes in extreme precipitation indices over these regions

Summary

Introduction

Precipitation extremes are one of the major factors that trigger natural disasters, such as droughts, floods and landslides, which subsequently cause the loss of property and life, and deteriorate socioeconomic development. Under the prevailing anthropogenic warming, the precipitation extremes are observed to be intensified globally, exacerbating the existing problems of food and water security as well as disaster management [1,2,3,4,5,6,7,8,9,10,11]. Has experienced an overall increase in precipitation extremes [11], though such a pattern is heterogeneous across the region [5,11,13,14]. Studies have found a rise in the summer monsoonal precipitation extremes over central India and northeastern Pakistan [15,16,17,18,19,20]. Precipitation extremes feature a falling trend over southwestern Pakistan [20], the eastern Gangetic plains and some parts of Uttaranchal, India [21]. Contrary to the extremes observed at low altitudes or over the plains, extremes observed in the high-altitude mountainous regions exhibit quite an opposite sign of change due to the influence of local factors, and are less predictable [22]

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