| Precise analysis of spatiotemporal patterns of precipitation,temperature and agro-meteorological droughts play a central role in the sustainable management of water resources in the region.Various types of methodologies based on entropy theories,climatic trends statistics,drought indices and future forecasting approaches have been used in this study for the analysis of historical and future meteorological changes and drought anomalies with the aim to provide a comprehensive study for the researchers and policy makers for the given region.This study has been conducted at the eleven meteorological stations in the Songhua River basin of Heilongjiang Province,China.Firstly,spatial and temporal variability of the precipitation has been analyzed by using the entropy base concept.Sample entropy was used on the basis of monthly,seasonally,annually,decade and number of rainy days on the precipitation data for each meteorological station.Intensity entropy was applied to calculate the variability over the individual year and apportionment entropy was used to calculate the decadal variability.The results of sample disorder index displayed that precipitation during February(mean 1.09,max.1.26 and min.0.80)and July(mean 1.10,max.1.20 and min.0.98)contributed significantly higher.Similarly,precipitation variability on decade basis is increasing from decade 1964-1973 and 1994-2003 with average value of decadal apportionment disorder index 0.023 and 0.053,respectively.Secondly,long term climatic trends(monthly/seasonally and annually)of historical precipitation and temperature data series have been investigated by using the Spearmen's Rho and Mann-Kendall trend test at 5%significant level.The analysis of monthly precipitation showed significant(p<0.05)increasing trends during the winter(November and December months)season.Similarly,the results of seasonal and annual air temperature revealed a significant increase from 1.0 ? to 1.5 ? for the past 49 years(1965-2013)in the basin.According to the results of Sen's slope estimator,the rate of increment in seasonal temperature and precipitation slope were greater than annual air temperature and precipitation.Thirdly,meteorological drought has been identified by applying four well known drought indices named as Standardized Precipitation Index(SPI),Reconnaissance Drought Index(RDI),Standardized Precipitation Evaporative Drought Index(SPEI)and Effective Drought Index(EDI)at various time scales(3,6,9 and 12-months)by using historical time series data.Moreover,Mann-Kendall trend test at 5%significant level was applied for the assessment of drought trends in the basin.Drought results indicated that the 12-month data series for Songhua River Basin is appropriate for the assessment of drying conditions and for comparison of different drought indices.The Pearson's correlation analysis between drought indices results and meteorological variables(i.e.precipitation)revealed that SPI is better drought index for the assessment of drought(r=0.99).Severe and extremely dry conditions prevailed in the study region during the years of 1990 and 2001 in the study area.Furthermore,drought indices that compute the drought events by their drought initiation,termination time and statistical properties such as frequency,severity,intensity and duration are practically stratagems for the estimation and monitoring the impact of drought events on the region.This study also investigated the agricultural drought trends and their characteristics by using the Standardized Soil Moisture Index(SSI).Additionally,Multivariate Standardized Drought Index(MSDI)was also used for the assessment of the composite effect of both agricultural and meteorological droughts.The results showed that most extreme and exceptional drought occurred during 2004-05.The spatiotemporal analysis indicated that Annual Drought Frequency(ADF,1.20 to 2.70),Mean Drought Duration(MDD,5 to 11 month),Mean Drought Severity(MDS,-0.30 to-.9)and Mean Drought Intensity(MDI,-0.2 to-0.70)were found over the study area during the study period.The results also indicated that MSDI identified the drought onset earlier as compared to SSI.Overall,the finding justified the suitability of MSDI as an alternative tool for the evaluation and monitoring of agricultural and meteorological drought events and provides an insight to choose the appropriate time scale and drought index for a specific region to identify the severities of drought.Fourthly,future forecasting analysis of meteorological droughts have been assessed by using the statistical downscaled meteorological data of CMIP3 and CMIP5 approach.CMIP3 uses an emission scenarios from the Intergovernmental Panel on Climate Change while Representative Concentration Pathways(RCP)were used in CMIP5.CMIP5 used three Representative Concentration Pathways namely RCP2.6,RCP4.5 and RCP8.5.Reconnaissance drought index(RDI),effective drought index(EDI)and standardized precipitation index(SPI)were used for precisely prediction of the occurrence of future drought events in the study area.The drought indices were computed from the meteorological data(temperature,precipitation)generated by the global climate models of CMIP3 and CMIP5.Moreover,the Mann-Kendall trend test was applied for the assessment of future climatic and drought trends in the study area.Drought forecasting period was divided into three categories:the early phase(2016-2030),middle phase(2031-2060)and late phase(2061-2099).The occurrence of future droughts is also ranked according to their intensity(mild,moderate,severe and extreme drought).Based on the drought results,more extreme droughts are expected to occur during 2070-2090 with an intensity of(minimum EDI value)-4.00.The most severe droughts would be expected to occur during 2030-02050 with an intensity of(minimum EDI-3)-1.93 and during 2085-2090 with an intensity of(minimum EDI-3)-1.87.Similarly,most moderate droughts are projected to occur during 2080-2090 with an intensity of(minimum RDI)-1.47.The January and February months of the years studied predicted a warming trend,while the 7th,8th,and 9th months predicted a wetter trend.Finally,it was observed that EDI indicated a high percentage of drought years under severe and extreme drought conditions,while RDI presented a good performance for the assessment of mild and moderate droughts during the drought frequency analysis.The results of CMIP5 showed that RCP8.5 and RCP 4.5 predicted more number of years are expected under severe droughts conditions.Moreover,RCP4.5 outcomes showed that a more number of years are projected under mild and moderate droughts condition in the study area.Conclusively,the analysis and quantifications of this study provides a mechanism for the policy makers to mitigate the impact of extreme climate and agro-meteorological drought(historical and future)conditions in order to improve local water resources management in the region. |
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