| Nepal is traditionally an agrarian country.Agriculture employs more than 75% of the population and accounts for about 35% of GDP.It plays a significant role in improving the livelihoods and health of rural livelihoods.Extreme climate conditions,on the other hand,have severely harmed this industry in recent decades.Drought is one of the most serious impacts of climate change on agriculture.It is mainly caused by a lack of precipitation,which induces water stress and is activated by temperature.Drought research in Nepal is relatively new,with a focus on the causes,consequences,and effects on the agricultural sector.Therefore,the aim of this dissertation is to conduct a comprehensive study into drought,its causes,and effects on agriculture.This study was conducted in the Koshi River Basin,Nepal covering three regions,namely the mountain,hill,and low land(commonly called “Terai” in Nepal)regions of the from north to south.Sixteen districts that had maximum number of meteorological stations and agricultural data with the longest period have been selected.Thus,we selected 30 years of data for climate and crop yield from 1987 to 2016.Few numbers of focus group discussions and key informants' interview were also undertaken in some of the districts of the basin to validate our findings from the field.The data were processed using several methods and outputs were analyzed.The findings were tied up and established systematically.The comprehensive analysis of drought and its effect on agriculture in Koshi River Basin,Nepal would help stakeholders,policymakers,and local government by better understanding drought,its temporal and spatial phenomena,and impacts on major crop yields,as well as paving the way for mitigation and adaptation plans.First,the annual and seasonal trends of the climatic factors(precipitation,average temperature,and diurnal temperature range-DTR)primarily responsible for the drought were examined.The annual and seasonal trend covers the year round and the respective growing seasons of maize,rice,and wheat from 1987 to 2016.The non-parametric test of Mann-Kendall and Sen Slope was used to analyze trends and magnitude of climatic factors.Annual and seasonal trends have shown that there has been a significant increase in temperature and a decrease in precipitation in the KRB region over the 30-year period from 1987 to 2016.The annual average rate of significant trend over the region was-13.16 mm/year(precipitation),0.03 ?/year(average temperature),and0.02 ?/year(DTR).Average climatic factors during crop growing seasons also showed similar pattern and trend magnitude,except for wheat.In the wheat growing season,the precipitation trend decreased only at a rate of 0.24 mm/year.However,the highest declining precipitation rate in maize,rice and wheat growing seasons among the districts studied was 15.09 mm/year,19.1 mm/year and 3.73 mm/year,respectively.Similarly,average temperature(diurnal temperature range)was observed to be increased by 0.08(0.11),0.08(0.09),and 0.10 ?(for both)respectively.These trends in climatic factors have shown that meteorological,agricultural,and hydrological droughts can prevail in the region.The overall rising temperature trend in growing seasons and the declining precipitation trend in maize and rice growing seasons may be more sensitive and may have negative effects on future crop yields.The potential negative effect should therefore be minimized by adopting modern agricultural technologies at local level through advocacy and short-term,mid-term and long-term implementation plans(Chapter 4).Second,based on climatic factors(precipitation and temperature),the trend and spatial-temporal analysis of drought and its characteristics over the Koshi River Basin(KRB)in Nepal was examined using the Standard Precipitation Evapotranspiration Index(SPEI)over the period 1987 to 2017.The Mann-Kendall test was used to determine the trends of the SPEI values.The study illustrated the increasing trends in annual and seasonal droughts in the KRB over the study period.Spatially,the KRB hill region has shown a significant increase in annual and seasonal drought trends,especially in summer and winter.The mountain region has also shown a significant increase in the trend of winter drought.The analysis of drought characteristic showed that the maximum duration,intensity,and severity of drought events were observed in the KRB after 2000.As a result,these features of drought have also been observed in the ten-year time scale of the entire basin.The study period from 1987 to 2017 was divided between 1987 and 1996,1997 and 2006 and 2007 and 2017.The frequency of drought increased by 20 % between 1997 and 2006 and by 13 % between 2007 and2017,compared to 1987 and 1996.Similarly,the number of drought events increased from 6 to 8 in the last twenty-one years(1996 to 2017)compared to 1987 to 1996.The average duration of drought increased by 4 months between 2007 and 2017 from 1987 to 1996 and by 5 months from 1996 to 2006.Similarly,the maximum duration of drought increased by 6 months between 2007 and 2017 compared to 1987 and 1996 and by 9 months compared to 1996 and 2006.Spatially,the Terai region had the highest drought frequency and intensity,while the hill region had the longest maximum drought duration.The spatial extent of the drought has shown a significant upward trend in the hill region during August(7.6 % decade-1)and summer(7.2 % decade-1).The findings clarify the drought and its implications at the local level(Chapter 5).Third,this study conducted a quantitative assessment of crop yield losses in response to drought.It estimated and analyzed the spatial-temporal patterns of crop loss in the mountain,hill,and lowland regions of the Koshi River Basin(KRB)of Nepal over the period 1987 to 2016.We used the Lagrange interpolation method to estimate the expected crop yield and therefore to estimate crop loss.The findings showed that the average crop yield loss(kg/ha)was frequent after 2000 and the maximum maize yields(1977 kg/ha),rice(979 kg/ha)and wheat(853 kg/ha)were found to be lost in the Terai,hill and mountain regions,respectively.The highest average loss rate of rice and wheat yield(12.51 kg/ha/year and 16.21 kg/ha/year)in the Terai region was the highest in mountain and maize yield losses(19.16 kg/ha/year).The analysis of the sequential Mann-Kendall test revealed most of the abrupt changes in the regions that occurred after 2000.The abrupt change in the yield loss of wheat was observed in 2009 with a significant upward trend in the mountain region after 2013.Similarly,there was a significant increase in maize(after 1995)and wheat yield losses(between 1990 and1999)and a significant decline in rice yields(after 2002)in the hilly regions.The wavelet analysis for periodic variations in maize,rice and wheat also showed a significant loss of yield after 2000 in these regions between 1987 and 2016.The characteristics of the first and second key periods for crop yield loss showed a variation period and predicted crop yield loss would result in a high yield loss or a low yield loss period in a short period after 2016.The findings of this study provide a detailed intervention in the assessment of crop yield losses at river basin level(Chapter 6).Fourthly,this study analyzed the impact of drought on maize,rice,and wheat crop yields(kg/ha)between 1987 and 2016 using a correlation analysis and a linear estimation method.Spatiotemporal features of drought have also been observed using the standardized precipitation evapotranspiration index in the three regions of the Koshi River Basin,Nepal.The results showed that drought was sensitive during crop growing seasons in the 1990s(especially in 1992 and 1994),after 2000,and that drought rates in the seasons increased between 1987 and 2016 as well.The hill region has shown a more significant increase in drought trends during crop growing seasons at different drought times than the mountains and the Terai.Maize yields are more vulnerable due to an increasing drought trend in all regions.The change in crop yield estimated based on expected and actual yields has shown that crop yield losses are massive in the regions.The highest average yield losses for maize(660 kg/ha)in the Terai,rice(345 kg/ha)in the hills and wheat(308 kg/ha)in the mountains during the study period were among the crop losses in the regions.The correlation between the detrended standardized potential evapotranspiration Index(SPEI)and the crop yield change shown in maize is sensitive to early drought in the Terai and mountain regions,whereas the same crop was affected in later stages in the hills.Rice yields are sensitive to drought from the late vegetative stage to the entire growth phase in the hills and the Terai region.The analysis showed a weak positive relationship for wheat yield in all regions.The findings of this study can help to understand the drought and crop yield impacts of recent decades and help stakeholders plan drought contingency and mitigation planning in the agricultural sector(Chapter 7).The overall findings of this study therefore provide a comprehensive understanding of the drought and its consequent impact on agriculture.It can help local governments,planners,and project implementers to understand the drought and develop appropriate mitigation strategies to address its impacts.It also provides for detailed intervention in the assessment of crop loss at river basin level and can provide an important pathway for the development of a crop loss mitigation plan in the agricultural sector to achieve self-reliant and sustainable agricultural productivity.It can help to understand the impact of drought on crop yields in recent decades and help stakeholders plan for drought contingency and mitigation planning in the agricultural sector.Chapter 8provides a summary,conclusion and recommendations based on research outputs and recommends further study in the future. |
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