Stationarity in the variability of arid precipitation:A case study of aridCentral Asia

Precipitation is particularly scarce in arid Central Asia(CA),and is expected to be severely impacted by future warming,and the assessmentof the stationarity of precipitation variability is important for managing surface water resources in this region.In this study,we investigated thestatistics of stationarity in the totals and extremes of precipitation in CA based on the longest observational records(1881e2006),tree-ringreconstructed records(1756e2012 and 1760e2015),and the Coupled Model Intercomparison Project 5(CMIP5)simulations,applying theautocorrelation function and testing criteria established based on the statistical definitions of stationarity.We analyzed the longest daily pre-cipitation record(Tashkent station,1881e2006)and found that the autocorrelation coefficient of the precipitation totals(PRCPTOT)and annualmaximum 1-day precipitation amount(Rx1day)were statistically insignificant for all lags,implying stationary behavior.Regionally,nearly allthe Global Historical Climatology Network-Daily Database(GHCN-D)observatory sites(1925e2005)indicated likely stationary behavior.Thereconstructed records were also indistinguishable from a random process.For the CMIP5 models,the simulated and projected PRCPTOT closelyapproximated a purely random process;however,the projected Rx1day maintained non-stationary means in most of the models under therepresentative concentration pathway(RCPs),implying that extreme events would increase in the future.The mean precipitation changes(DP)can be expressed as an exponential function depending on the length of the successive mean periods(m)and variance(s2).TheDPof the nextdecade is projected to be within±14.8%of the previous decades mean annual PRCPTOT over CA.The higher the RCPs,the higher theDP overCA.The results show that the detection and prediction of precipitation change will be challenging in arid CA.