

Effect of Short and LongTerm Memory on Trend Significancy of Mean Annual Flow By MannKendall Test



نویسنده

Ghahraman B.

منبع

International Journal Of Engineering  2013  دوره : 26  شماره : 10  صفحه:1155 1168



چکیده

Climate variability and change is threatening water resources around the world. one hundred and fourteen (114) stations from reference hydrometric basin network (rhbn) around canada with at least 30 years continuous data (up to 2011) were selected to studythe trend in mean annual runoff for different periods of 30 to 100 years in step 10 years by nonparametric mannkendall test. effect of short term persistent (stp) and long term persistent (ltp) on this test were made through lag 1 serial correlation (ρ1) and hurst exponent (h), respectively. ρ1 for about one third of the total cases considered was negative. h, based on equivalent normal deviate (env), was slightly rightskewed with minimum and maximum values of 0.20 and 0.87, respectively. about half of the data sets were antipersistent (h<0.5). no regional pattern was found for ρ1 and h. based on five stations with around 100 years data it was shown that ρ1 and h are unstable for record length, roughly, up to 50 years. ρ1 and h were highly correlated (r=0.86). hfrom end were smaller than h from original data by around 10% with high correlation (r=0.87). under classic mannkendall trend test, different time periods of different stations showed different trend direction and significancy, which admits for abrupt change in trend direction and significancy for different time periods. on overall, more than 60% of cases there were no significant trends (i.e. pvalue>0.1). the number of positive and negative trend, were nearly the same, though fluctuating for different time spans. pvalue after prewhitening was highly correlated with those of before prewhitening, for both negative and positive trends. there were about 16% of cases that prewhitening decreased the pvalues of the mannkendall trend test, where nearly all of them werenegatively trended. the effect of ltp on mannkendall trend test was minor due to inconsistency of originally significant trend case and significant h of greater than 0.5. for recent 30 years length of record (19822011), british columbia is experiencing positive trend in the west and negative trend in the east. most parts of the new brunswick are experiencing the positive trend, while negative trend is due to southeast of ontario. for the longer duration of 40 years, trend statistics and geographical pattern were changed. while the significant trends are decreased, more significant negative trends are governed over new brunswick. there is no positive trend in british colombia in the past50 years (19622011) while there are both negative and positive trends in new brunswickwhich negative trends are switched to positive trends in south east of ontario. for long duration of > 70 years, there are only positive trends in southeast of canada (south new brunswick and south east of ontario) while central and east of canada have experienced a negative trend. © 2013 elsevier b.v.

کلیدواژه

Climate Change; Climate Variability; Hurst Exponent; Hydrology; Lag 1 Serial Correlation; LongMemory Process

آدرس

Ferdowsi University Of Mashhad, ایران












