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Nanjing University of Information Science and Technology (2022)

Climate Change in Pakistan:A Comparative Analysis of Precipitation Using Satellite,Reanalysis,and Numerical Models

Muhammad Arshad

Titre : Climate Change in Pakistan:A Comparative Analysis of Precipitation Using Satellite,Reanalysis,and Numerical Models

Auteur : Muhammad Arshad

Grade : Doctoral Dissertation 2022

Université : Nanjing University of Information Science and Technology

Remote sensing and reanalysis products are at the core of quantifying hydrological cycle and its response to climate change.However,uncertainties of these datasets limit their applications at regional scales,especially in hilly,remote,and sparsely populated places,where there is not enough rain gauge data for validation.This study focused on Pakistan,a developing country with a land area of 796,100 km 2 but limited precipitation observing stations.To assess the suitability and practicality of remote sensing and reanalysis precipitation products in this region,a comprehensive examination of these products was conducted to evaluate the precipitation spatiotemporal variability,extreme events,and temperature change.Specifically,the current study accomplished the following objectives:1)Long-term(1981–2020)spatiotemporal distributions of Precipitation and Temperature(i.e.,Tmax and Tmin)and their trends were investigated over Pakistan.The influences of large-scale atmospheric circulations and warming mechanisms associated with precipitation and its extremes were investigated.Long-term spatial distributions of annual mean precipitation demonstrates the higher precipitation(1200-1600 mm/year)over the northern parts of Pakistan.The Sen’s Slope and Mann–Kendall test show the 95%statistically significant increasing trends of precipitation(>10 mm/year)and decreasing trends of Tmax(0.06°C/year)across the eastern and southern parts of Pakistan.Moreover,precipitation is found to be significantly decreased(-2.1 mm/year)in cold(winter)season,whilst it is increased during the warm(monsoon)season(1.6 mm/year).The results suggest that precipitation variability over Pakistan has a weak relationship with El Nino/Southern Oscillation,Indian Ocean Dipole,and monsoon onset timing.2)The Satellite-based Precipitation Products(SPPs)such as Precipitation Measurements(GPM)products from Integrated Multi-satellite Retrievals,early run(IMERG-E),late run(IMERG-L),final run(IMERG-F),and Tropical Rainfall Measuring Mission(TRMM-3B42))were evaluated against the rain gauge data from 2004 to 2018.Several statistical metrics namely were used to assess the performance of SPPs and the results showed a good agreement between SPPs of IMERG-F and the rain gauge data.Notably,both datasets were showing higher(800 mm)and lower(100 mm)precipitation across the northern and southern parts of Pakistan.3)The Reanalysis Precipitation Products(RPPs)provide more detailed insights into many aspects of regional evaluation.The reanalysis products’evaluation stipulates that the ERA-5 performed well amongst the all RPPs,consistently captured the precipitation intensities(light to violent)and extreme precipitation events(95th percentile),followed by CFS-2.The MERRA-2 did not detect extreme precipitation events in some regions.The JRA-55 produced good results in the central area while overestimated the precipitation in the northern and southern parts of the study area.4)Furthermore,the Weather Research and Forecast(WRF)model was used to understand the relative behavior of various microphysics schemes on precipitation simulation.WRF model simulations were performed using reanalysis of ERA-5 and Final Analysis(FNL)datasets as initial and lateral boundary conditions with two microphysics schemes,Single Moment 6-class(WSM6)and Lin(WL)over the Punjab,Pakistan at seasonal scales.The results of the WRF model simulation demonstrated that each simulation scheme performed differently for each season.Results from the ERA5-WSM6 simulation are more accurate in winter,monsoon,and post-monsoon seasons,while the FNL-WL simulation performed well in pre-monsoon.The large scale oceanic and onset of monsoon has less influence over the precipitation variation and thus need further exploration including the influence of Himalayan(Tibet Plateau)thermal forcing.Even though,the station data is subjected to deviation,and uncertainties the current study have reported diverse variability of the precipitation and thus a follow up study is recommended to model the influence of such indices on precipitation variability over Pakistan

Mots clés : Climate Change ;Precipitation Trends ;Satellite Data ;Reanalysis Products ;Pakistan;

Présentation (CNKI)

Page publiée le 17 octobre 2022