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Nanjing University of Information Science and Technology (2022)

Observed and Projected Changes in Drought Risks over South Asia under Global Warming Scenario

Irfan Ullah

Titre : Observed and Projected Changes in Drought Risks over South Asia under Global Warming Scenario

Auteur : Irfan Ullah

Grade : Doctoral Dissertation 2022

Université : Nanjing University of Information Science and Technology

Résumé partiel
In the recent past,South Asia(SA)has faced detrimental droughts due to changing climate that affected water availability,agriculture production and disrupted the lives of more than 2-billion people.Generally,SA droughts are primarily driven by the failure of the summer monsoon(June-September)providing 78% of the total annual rainfall,which is a lifeline for the millions of people across the region.The interannual variations of the summer monsoon precipitation in the region are associated with the large-scale atmospheric and oceanic circulations,particularly El-Ni( ?)o Southern Oscillation(ENSO),Pacific Decadal Oscillation(PDO),and the Indian Ocean Dipole(IOD).The weakening of the summer monsoon precipitation can cause meteorological droughts,which,if prolonged,could propagate hydrological to agriculture droughts.Drought risk in SA has been changing under the observed and projected climate,however,it is still unclear how the drought frequency and severity in the observed climate could affect the water resources,agriculture activities,and socioeconomic growth with a warmer climate over SA.Nevertheless,major droughts have posed insightful challenges in all the spectrums of lives across SA,little is known about their features and drivers in a future warming climate.Moreover,there might be substantial uncertainty in the characteristic of the worst droughts in distinct reanalysis datasets,which has not been carefully evaluated over SA.The present study characterizes the observed and future changes in amplified drought risks across SA and its sub-regions under changing climate.The in-situ observational and reanalysis datasets of the Climatic Research Unit(CRU TS),National Centers for Environmental Prediction version II(NCEP-2),European Centre for Medium-Range Weather Forecasts Version-5(ERA-5),Modern-Era Retrospective Analysis for Research and Applications version II(MERRA-2),and projections from the phase six of the Coupled Model Inter-comparison Project(CMIP6),models have been analyzed.Different statistical metrics,anomaly analysis,Bayesian Dynamic Linear(BDL)model,climate indices,run theory,and multivariate return period approaches were used to assess the observed and future changes in meteorological drought.This study employed two Shared Socioeconomic Pathways(SSPs)and warming targets,i.e.,(SSP2-4.5 and SSP5-8.5)and(1.5 and 2 oC),respectively.Firstly,this study sought to evaluate the performance of reanalysis products against in-situ observations over diverse regions of Pakistan as a representative of the South Asian region.Secondly,the study provides detailed assessments of observed changes in seasonal drought characteristics and their potential drivers over Pakistan.Moreover,the study assesses recent changes in drought episodes and their possible linkage to atmospheric circulation and human influences over SA.Finally,the research investigated the future changes in increased drought risks over SA and its sub-regions under 1.5 and 2 oC warming levels.The main conclusions of the study are as follows:1)Drought indices and drought areas assessed from reanalysis products are more representatives of historical droughts in southern Pakistan,and overestimation is evident for drought severity in western than eastern Pakistan.Statistically significant increasing trends(1984-1998 and 2000-2010)in monthly drought areas and occurrence are evident by CRU TS and MERRA-2 in dominant arid and semi-arid regions.Climate variables and drought features of southern Pakistan are best represented by CRU TS and MERRA-2,while ERA-5 best represents that of southwestern and western parts.The Nash–Sutcliffe efficiency(NSE)result ranges from-2 to 0.9,where the NSE of SPEI values(-1.0)show relatively weaker than SPI values(0.5)in most parts of the regions,specifically in southern Pakistan.A strong positive linear relationship on a monthly scale is evident in CRU TS,MERRA-2,and ERA-5 exhibiting relatively high correlation coefficient(0.84),except for NCEP-2 ;2)An increase in drought severity was revealed mostly over arid and semi-arid regions for both cropping seasons.While temperature played a significant role in defining droughts over dry and hot seasons,rainfall is influential over the western disturbances-influenced region.

Mots clés : Climate Change ;Drought Risks ;Large-scale Climate Drivers ;Socioeconomic Exposure ;South Asia ;

Présentation (CNKI)

Page publiée le 18 octobre 2022