Assessment of drought impacts on crop yields across Nepal during 1987-2017

Drought influences agriculture, hydrology, ecology and socio-economic systems globally. As agriculture is the primary source for livelihoods and contributes to similar to 27% of Nepal s total gross domestic product, it is essential to understand the impact of drought on maize and wheat crop yields to minimize the drought-related risks. This study presents insights about agricultural drought across Nepal during 1987-2017 using the Standardized Precipitation Evapotranspiration Index (SPEI). The temporal evolution of SPEI time series has revealed frequent occurrences of drought episodes during the cropping cycle of summer maize and winter wheat crops. Moreover, the turning point of the drought was detected in 2000 (1987-2000, 2001-2017) in different regions. The averaged frequency for the SPEIs (1, 3, 6 and 12) of drought years for summer maize (winter wheat) in the western, central and eastern regions increased by 13% (12.5%), 6% (7.5%) and 7% (8%), respectively, from 1987-2000 to 2001-2017. The relationship between Standardized Yield Residual Series, the detrended SPEI at 1-12 lags and soil moisture was observed for both crops. The most correlated crop growth period for summer maize and winter wheat was the sowing and growing period, respectively, indicating the sensitive period of water deficit. Besides, the correlation performed in the two sub-periods (1987-2000 and 2001-2017) shows that drought impacts increased in the western and central regions, whereas they substantially decreased in the eastern region during the cropping period of summer maize. However, the drought sensitivity for winter wheat was decreased in the western region but significantly increased in the central and eastern regions of Nepal. The results of this study provide important information useful for policymakers in monitoring and mitigating the drought-related risks on maize and wheat crops in Nepal.