Rising Precipitation Extremes across Nepal

Abstract

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 . 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.

Spatial and Temporal Analysis of Precipitation Extremities of Eastern Nepal in the Last Two Decades (1997–2016)

“…Nineteen out of 24 stations showed an increasing trend ( 15 statistically positive trends ), inferring that the area is being drier and drier in the last two decades. This finding is consistent with the previous studies (Karki et al, ; Shrestha et al, : Sigdel & Ma, ). The CDD was found to be increasing on an average rate of 1.1 days/year.…”

Mapping and Attributing Normalized Difference Vegetation Index Trends for Nepal

“…On the other hand, in boreal areas, warming has been a major driver of longer growing seasons and higher productivity [51,52], while in arid and semiarid areas, moisture availability is a primary modulator of vegetation growth [15,[53][54][55]. The small positive impact of precipitation on NDVI trends, concentrated during and after the summer monsoon, is consistent with the increasing trend in monsoon precipitation found for recent decades over much of Nepal [56], although dry spells have also increased [57,58].…”

Climate Changes and Their Impact on Agricultural Market Systems: Examples from Nepal

“…This is partly in contrast with researchers' measured data. Different studies, such as that by Karki et al [63], do show a decrease in precipitation over the central and eastern mid-hills. The same decrease in annual precipitation in the central mid-hills in the Nuwakot district is depicted by Poudel and Duex [64], who show that 73.2% of springs decreased and 12.2% dried up over the past 10 years.…”