| The widely used standardized precipitation index(SPI)is obtained by fitting precipitation data using the gamma distribution with constant parameters under the assumption that the precipitation time series is stationary.However,in the context of global climate change,the stationary assumption of precipitation is questionable.Therefore,in this study,the non-stationary gamma model with variable parameters is established by fitting the model parameters with climate indices as explanatory variables based on a Generalized Additive Model in Location,shape(GAMLSS),and the non-stationary SPI(NSPI)is calculated and its applicability in the Yangtze River Basin(YRB)is discussed.Then,based on the NSPI,the spatiotemporal characteristics and joint return period of meteorological drought are analyzed in the YRB,and the health status of the YRB at different time scales is evaluated by using the reliability,resilience and vulnerability(RRV)indicators.The results are as follows:(1)The changing trends of the NSPI are roughly consistent with those of the stationary SPI(SSPI),but the non-stationary model can better reproduce the precipitation to capture precipitation variation in the context of global climate change.This indicates that the NSPI is more suitable to reflect the drought situation in the YRB.In addition,for the same typical extreme drought event,the drought estimated by SSPI is more serious than that estimated by NSPI.(2)There exist obvious temporal and spatial differences for the droughts over the YRB.The west of the basin experiences mostly severe droughts but shows a mitigating tendency,while in the north-central region,the moderate droughts are dominant but have an aggravating tendency.Drought peak shares a spatial distribution pattern similar to intensity,with higher averages in the west and south-central of the basin,and lower averages in the north-central part but exhibiting a higher occurrence frequency of droughts.(3)The joint return periods of drought characteristics reveal that the slight and moderate droughts with duration of less than 3 months are more likely to occur in the YRB with return periods of less than 25 years.The severe and extreme intensity droughts with duration of more than 3months occur hardly in the YRB,but the extreme peak droughts with slight or moderate intensity could hit most of the basin in 100 years.Additionally,for the most of drought scenarios,the droughts exhibit longer return periods in the north-central and southeast parts compared to other regions of the YRB.(4)The results of RRV comprehensive indicator show that the most regions of the YRB are in the state of general health level at different time scales.The stations with significant upward trends are mainly distributed in the west of the YRB,while the central-south and southeast of the basin show a significant downward trend.For the resilience indicator,it is found that the spatial distribution at 5-year time scale is different from those at other time scales,but the smaller values are mainly distributed in the source area of the Yangtze River.However,for the reliability indicator,there exists little difference at the different meteorological stations at the same time scale as well as the same meteorological station at different time scales,and their values are all above 0.80,which indicates that the probability of being a satisfactory status is large at each time scale in the basin. |
