Spatiotemporal analysis of drought variability based on the standardized precipitation evapotranspiration index in the Koshi River Basin, Nepal

Drought is an inevitable condition with negative impacts in the agricultural and climatic sectors,especially in developing countries.This study attempts to examine the spatial and temporal characteristics of drought and its trends in the Koshi River Basin(KRB)in Nepal,using the standardized precipitation evapotranspiration index(SPEI)over the period from 1987 to 2017.The Mann-Kendall test was used to explore the trends of the SPEI values.The study illustrated the increasing annual and seasonal drought trends in the KRB over the study period.Spatially,the hill region of the KRB showed substantial increasing drought trends at the annual and seasonal scales,especially in summer and winter.The mountain region also showed a significant increasing drought trend in winter.The drought characteristic analysis indicated that the maximum duration,intensity,and severity of drought events were observed in the KRB after 2000.The Terai region presented the highest drought frequency and intensity,while the hill region presented the longest maximum drought duration.Moreover,the spatial extent of drought showed a significant increasing trend in the hill region at the monthly(drought station proportion of 7.6%/10 a in August),seasonal(drought station proportion of 7.2%/10 a in summer),and annual(drought station proportion of 6.7%/10 a)scales.The findings of this study can assist local governments,planners,and project implementers in understanding drought and developing appropriate mitigation strategies to cope with its impacts.

Climate-driven changes in drought metrics across the Yellow River Basin based on Coupled Model Intercomparison Project Phase 6

Recent climate change has accelerated the global hydrological cycle, substantially affecting drought metrics such as drought duration and drought propagation;however, knowledge of drought patterns in these metrics remains limited. Here, we aimed to address the evolution and influencing factors of major drought metrics under past and future climate scenarios within the Yellow River Basin(YRB) based on Coupled Model Intercomparison Project Phase 6(CMIP6). Accordingly, we investigated the changes in drought duration for meteorological drought and agricultural drought across the YRB and identified the variability in drought propagation time from meteorological drought to agricultural drought by using a standardized precipitation/soil moisture index and run theory. Meteorological and agricultural drought duration, and propagation time, increased from 1850 to 2014, decreased significantly from 2015 to 2100 with change trends of –0.0027, –0.0197, and –0.002 month/year, respectively. Drought duration had a negative sensitivity to humidification, and agricultural drought was more sensitive than meteorological drought. Propagation time exhibited a greater sensitivity to meteorological humidification than agricultural humidification. The results also suggest that precipitation, evapotranspiration, and soil moisture are the main drivers of drought metric changes, with air temperature and crop cover exhibiting a strong indirect effect on drought metrics in the YRB. Decreased propagation time from meteorological to agricultural drought and decreased duration provide evidence for the accelerated occurrence and increased impact of drought, highlighting the importance of a more comprehensive understanding of drought metric changes under rapid climate change.